School Science Lessons
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34.0 Materials

Table of contents

See: Mechanics, (Commercial)

34.6.0 Bridges



3.66.7 Coade stone

34.7.0 Coefficient of restitution

36.3.01 Elements in the Earth's crust

36.3.02 Elements in the Sun

34.9.0 Environment pollution

34.2.0 Heat treatment

34.3.0 Materials from the Earth

4.99 Materials that absorb sound

34.5.0 Mechanical properties

35.4.0 Rocks & minerals

34.5.3 Shear stress

34.5.2 Tensile & compressive stress

3.66.5 Mortar, sand and slaked lime, sand and cement
3.66.6 Portland cement
3.66.1 Tests for cement brick strength (contents)
3.66.2 Tests for cement brick strength (water content)
3.66.4 Tests for cement change in weight when setting
3.66.3 Tests for concrete alkalinity

35.4.0 Rocks and minerals, general properties
35.4 Rocks and minerals, definitions, mineral classification and origin
35.9 Cleavage, fracture, twin crystals, crystal face
35.5 Colour
35.8 Crystal systems, crystal habit, crystal form
35.18 Feel and conductivity
35.6.0 Geological time scales
35.17 Grain size and roundness
35.10 Hardness, Mohs scale of hardness
35.13 Hydrochloric acid test, effervescence
35.6 Lustre (metallic lustre, non-metallic lustre)
35.14 Magnetism test
35.15 Odour and taste
35.11 Relative density, r.d. (formerly specific gravity)
35.19 Shape or form
35.12 Streak
35.20 Tenacity
35.12.1 Touchstone, gold streak
35.7 Transparency (transparent, translucent, opaque, refraction)

34.6.0 Bridges
34.6.1 Classification of bridges (GIF)
34.6.4 Truss systems (GIF)
34.6.3 Simple cantilever, used in building porches, (GIF)
34.6.2 Test the strength of a simple bridge

34.7.0 Coefficient of restitution, bounce
34.7.1 Bouncing balls, Silly putty, silicone, bouncing putty, "Tricky Putty"
34.7.2 Coefficient of restitution (coefficient of elasticity)
34.7.3 Dead and live balls

34.9.0 Environmental pollution
34.9.5 Electrostatic precipitation
34.9.2 Noise sources, Test A
34.9.3 Noise control, Test B
34.9.4 Pollution from light of buildings
34.9.1 Pollution from noise, noise effects, thinking and learning, white noise

34.2.0 Heat treatment of metals
34.2.2 Annealing
34.2.1 Heat treatment of needles Heat treatment of razor blades or steel knitting needles
3.64 Heat treatment of steel needles, annealing, quenching, tempering
34.2.3 Quenching
34.2.4 Tempering

34.3.0 Materials from the Earth
34.3.0 Materials from the Earth
34.3.1 Lime (quicklime and slaked lime)
3.2.6 Make fibrous plaster board with plaster of Paris
34.3.2 Prepare quicklime
34.3.3 Prepare quicklime by slaking
3.68 Putty
3.65 Tests for strength of mud, clay, and sand bricks
3.67 Tests for strength of plaster of Paris bricks

34.5.0 Mechanical properties of materials
See: Mechanics (Commercial)
See: Mechanics, (Commercial)
See: Wire (Commercial)
34.5.0 Mechanical properties of materials, elastic, ductile, malleable Breaking strains, brittleness
34.5.03 Bulk modulus, modulus of incompressibility, K
34.5.01 Elasticity (Stress: tension, compression, shear)
34.5.02 Viscoelasticity, creep
34.5.04 Young's modulus, E, elasticity, stress and strain
34.5.04a Young's modulus experiments Young's modulus of students Coffee, coffee tins
34.8.6 Crystal faults, crushing salt
34.8.5 Crystal growth in a film Ductility and elongation of metal Hooke's law, elastic limit, deforming force, stress and strain
34.8.2 Ice model
34.8.4 Ice nuclei Lip balm Nail polish
34.5.06 Poisson's ratio, v
34.8.7 Shape memory alloy, Nitinol
34.5.05 Shear modulus, modulus of rigidity, G Shear stress
34.8.8 Solid models, sphere packing Strain gauge
34.6.3 Strength of paper, shape and its mechanical strength Stretch springs Toothpaste Toothpicks

34.5.3 Shear stress
See: Mechanics Structures Tester, stress and strain, (Commercial)
34.5.01 Elasticity (Stress: tension, compression, shear)
34.5.05 Shear modulus, modulus of rigidity, G
Experiments Plywood sheets, shear torsion Shear book, foam block Torsion rod, modulus of rigidity, bending and twisting

34.5.2 Tensile and compressive stress
See: Hooke's law, (Commercial)
See: Mechanics Structures Tester, stress and strain, (Commercial)
Experiments Bend beams, bend metre stick, stress rectangular bar, woods Bologna bottle, squeeze the bottle Breaking spaghetti Breaking threads Prince Rupert's Drops, tempered glass, toughened glass Sagging board, aluminium / steel elasticity paradox Shear strength of thin sheets Stretch a hole, deformation under stress, stress on a brass ring

3.66.1 Tests for cement brick strength (contents)
See diagram 3.65: Test the strength of a brick
See diagram 3.2.66: Cardboard box for cement test
Cement is any material that binds loose sediment into a rock and may be ferruginous (containing iron), calcareous (containing calcium),
and siliceous (containing silica).
Builders' cement contains calcium and aluminium silicates.
Concrete contains aggregate (gravel and sand), cement, and water.
Concrete can be cast into shape to become load bearing.
Mortar contains sand, cement and water and is used for plasters.
Grouts contain cement and water and are used to fill gaps.

Make 5 boxes out of stiff paper or cardboard 1.5 cm deep, 5 cm wide and 10 cm long.
Use adhesive tape or clips to fasten the edges.
A cement brick, the same size as the clay bricks, can be cast in these boxes.
Smear a little oil or grease around the inside surfaces of the boxes.
Obtain some fresh Portland cement from a builder.

1. Cement / water brick
Mix the cement with water to a thick paste and fill the box with it, smoothing off the top surface level with the paper.
It should "set" in a few minutes but it will take a few days to "harden".
"Setting" is to change from a fluid to a firm rigid material but a mark can still be scratched on the surface with a nail.
To "harden" is to become rock hard.

2. Cement / sand / water brick
Mix 1 part of cement powder with 3 parts of clean sand.
Work into a thick paste with water.
Pour into the paper box, smooth off the surface and leave to set and harden.

3. Cement / sand / gravel / water brick
Make a brick as before using 1 part cement powder, 1 part of sand, 3 parts clean gravel and water.
Cast the brick and leave to set and harden.
This is a concrete brick.

4. Cement / lime / sand / water brick
A builder buys quicklime and mixes this with water to make calcium hydroxide on the building site just before he uses it.
Mix 1 part of cement, 5 parts of builders' lime, calcium hydroxide, and 2 parts of sand and make into a paste with water.
Cast a brick as before and leave to harden.

5. Test the strength of the above bricks.

3.66.2 Tests for cement brick strength (water content)
See diagram 3.65: Test the strength of a brick
Wrap the waste cement in newspaper then put it in waste containers.
Do not pour cement paste down the sink.
Use identical cardboard milk cartons for moulds.

1. Put 200 mL of a mixture of dry cement and sand in a large beaker.
Slowly add 100 mL of water from a measuring cylinder, with stirring, to the mixture until it becomes a thick paste.
Pour the paste into cardboard mould.
1. Smooth the surface of the cement in the mould.
Wipe out the beaker with paper and rinse with water.
Record the volume of water used.
Repeat the experiment with 20% less water.
Pour the paste into cardboard mould.
2. Repeat the experiment with another 20% less in water.
Pour the paste into cardboard mould.
3. Repeat again with 20% more water than the mixture in mould 1.
Pour the paste into cardboard mould.
4. Repeat 1. and pour the paste into cardboard mould 5.
Cover the cardboard moulds 1 to 4 with plastic wrap to prevent evaporation.
Leave mould 5 uncovered.
Leave all the moulds in a warm place for 2 days.

Examine the mixtures:
1.1 Note the surfaces.
1.2 Scratch the surfaces with your fingernail, a nail, and the point of a file.
1.3 Drop a steel ball from the same height on the surfaces, while wearing safety glasses, and note the bounce height.
The harder the surface, the greater the bounce height
1.4 Remove the cardboard and use a hammer to hit each mixture with increasing intensity until it breaks.
Wear safety glasses when you do this.

2. Record the order of surface hardness by both methods and the resistance to breaking.
Note the relative hardness and the volume of water used.
Note the relative hardness of mould 1 and mould 5.
3. Repeat the experiment with the ratio of sand to cement from 50 mL of sand + 150 mL of cement, to 50 mL of cement + 150 mL of sand.
Test the strength of the above bricks

3.66.3 Tests for concrete alkalinity
Concrete is an artificial stone used as a building material.
It contains cement, sand, water and an aggregate, crushed stone or slag, a mixture of oxides formed during ore smelting and refining.
Reinforced concrete uses steel bars, twist bars, or cables to counteract weakness in tension.
Alkaline cement protects steel reinforcing rods in concrete from corrosion.
Clean pieces of steel reinforcing or nails with sandpaper
and put them into two jars half filled with water.
Put broken pieces of concrete in one jar.
After a week, note that the steel in the jar without the concrete corrodes faster.
Carbon dioxide from the atmosphere slowly penetrates the surface of concrete and reacts with lime, Ca(OH)2, to convert it to
limestone, CaCO3, reducing the alkalinity of the concrete touching the steel bars.
The steel can form rust containing iron oxides and hydroxides that have a larger volume than iron.
This expansion cracks the concrete.
Find a broken piece of old exposed concrete.
Break it and wet the new surface with phenolphthalein indicator solution.
A pink coloration indicates the high alkalinity inside the concrete with a rim of untinted concrete around the edge.

3.66.4 Tests for cement change in weight when setting
Weigh 500 g of sand and cement mixture (industrial mortar mix), into a polystyrene drink cup and add 75 grams of water.
Mix the contents until all the lumps are gone.
Weigh the polystyrene cup and contents again to check the weight of the added amount of water.
Fill another polystyrene cup with water to the same level and weigh the cup + water.
Leave the polystyrene cups for one day then weigh them again.
The loss in weight of the cup + water only shows the loss by evaporation of the cup + cement mixture + water.
The rough surface area of the setting concrete does allow water to evaporate faster than in cup + water only.
However, the loss by evaporation is negligible.
The experiment shows that most of the added water is absorbed in the chemical reaction of the setting cement.

3.66.5 Mortar, sand and slaked lime, sand and cement
Use 5 mL of slaked lime and 20 mL of clean sand.
Wash sea sand four times with water to get rid of the salty impurities.
Put the slaked lime into an old cup and make it into a paste with water.
Stir in the sand at a time, adding more water as needed, until a stiff paste forms.
Scrape out the paste on to a tin lid and leave it for a day or two.
It will set into a hard mass.
For a basic mortar, mix three parts of sand for every one part of cement you

3.66.6 Portland cement
1. Portland cement hardens as it reacts with water.
It was thought to have the same colour as stone on Isle of Portland, U.K.
Portland cement is a fine powder produced by grinding Portland cement clinker and some gypsum.

2. The raw mixture is mainly chalk or limestone containing clay or silicon dioxide and other materials, including clay, shale, sand, iron ore,
bauxite, flies ash and slag, i.e., minerals containing calcium oxide, silicon oxide, calcium aluminate, aluminium oxide, ferric oxide, and
magnesium oxide.
Calcium and silicon form the calcium silicates that give strength to the concrete.
Aluminium and iron compounds produce the liquid solvent flux in the kiln that helps in the formation of silicates at a conveniently low

3. The raw mixture is heated in a cement kiln at 1400-1450 oC so that the ingredients become sintered, i.e. about one third melted,
but not fused into a molten mass.
It cools to become grey-coloured clinker containing at least two thirds by weight of calcium silicates.
Calcium sulfate as gypsum is added to the clinker.
The gypsum hydrates very rapidly during the concrete setting reaction and helps to control the initial setting rate.
The mixture is ground to form fine cement powder that can be stored dry and later mixed with water to form an alkaline cement
workable slurry for casting.

4. Portland cement powder may contain 50% tricalcium silicate, 3(CaO).SiO2, 25% dicalcium silicate, 2(CaO).SiO2, 10% tricalcium
luminate, 3(CaO).Al2O3, 10% tetracalcium aluminoferrite, 4(CaO)4.Al2O3.Fe2O3, and 5% gypsum, CaSO4.2H2O.
So Portland cement contains approximately 65%, calcium oxide, CaO 25%, silicon oxide, SiO2, 5% aluminium oxide, Al2O3,
1% ferric oxide, Fe2O3 and 4% calcium sulfate, CaSO4.
Different types of cement contain the same four major compounds that make up at least 90% of the total weight, but in different
Tricalcium silicate + water (yields) --> calcium silicate hydrate + calcium hydroxide + heat

5. When water is added to concrete powder, hydration occurs and during this chemical reaction the concrete gradually hardens as
calcium silicate hydrate gel that forms in the first few days at the surface and later deeper in the pour.
The strength of hard concrete comes from the solid part of the paste, the calcium silicate hydrate and other crystalline phases.
The pores remaining in hard concrete are filled with water and air and have no strength.
dicalcium silicate + dicalcium silicate + water --> calcium silicate hydrate + calcium hydroxide + heat
The volume of setting concrete should not change because the added water should be used up in the hydration process.
So the weight of cement powder + water + aggregate = weight of the set concrete block (conservation of mass).
The water-cement ratio (by weight) of completely hydrated cement is 0.22 to 0.25, excluding evaporable water.
So the warning "Do not touch wet concrete until it dries" is inaccurate because nearly all the water is lost of the hydration reaction, not
by evaporation.
The rate of reaction of the cement with water is proportional to the surface area of the particles.
Cement production requires high energy input and produces large quantities of carbon dioxide, so it contributes to global warming.
However, EMC, Energetically Modified Cement, uses very finely ground ingredients that have increased surface area for the chemical
reaction and uses less energy to produce it.

3.66.7 Coade stone
Coade stone, "lithodipyra", was a popular artificial stone used before the invention of Portland cement, used for statues and sculptures.
It was famed to resist weathering and many statues and facades remain unweathered today.
It was made from a secret recipe of silica, alumina, flint, quartz, clay and soda-lime glass.

3.64 Heat treatment of steel needles, annealing, quenching, tempering
1. Annealing is used to produce a soft state in worked metals.
Heat a needle to bright red heat.
Hold it vertically in the flame and then take one minute to raise it slowly out of the flame.
Leave to cool.
Try to bend the needle with a pair of pliers.
The needle should now be soft.
You can easily bend it around a pencil.

2. Quenching is used to make steel metals harder and non-ferrous metals softer, e.g. copper.
Heat a needle to bright red heat and immediately plunge it into cold water.
Try to bend the needle with a pair of pliers.
The needle should now be brittle.
You can easily break it into small pieces.

3. Tempering of steel is reheating after rapid cooling to give extra secondary harness.
Heat a needle to bright red heat and immediately plunge it into cold water.
Use 5 cm sewing needles that are tough and springy and difficult to bend.
They are made of an alloy of iron with a small proportion of carbon.
Clean and shine the surface of the needle with emery cloth.
Heat the needle very gently until a deep blue oxide film appears on the surface.
This colour indicates the tempering temperature of the needle.
Leave to cool.
Try to bend the needle with a pair of pliers.
The needle is tough and springy again.

3.65 Tests for strength of mud, clay, and sand bricks
See diagram 3.65: Test the strength of a brick
1. Find a source of clay soil or mud.
If it is dry, it must be mixed with water.
To do this, put about 350 mL of water in a suitable container such as a plastic bowl.
Crush the dry clay to a powder and then mix it with water until a thick smooth paste forms.
Squeeze it through your fingers until no lumps remain.
It will have the correct consistency when it is thick and pliable and sticks more to itself than to your fingers.
Spread the clay or mud on to a flat surface very evenly to make a slab of 1.5 cm thickness.
Use a clean wet knife to cut four bricks, each 10 cm by 5 cm.
Dry one under the sun for two or three days and bake another by a fire.
Try making a sand brick of the same size.

2. Use a brick (house brick), sold by a building contractor.
See diagram 3.65: Test the strength of a brick
Examine the bricks for cracks.
Test whether the surface comes away by rubbing with a dry finger.
Test whether the surface comes away by rubbing with a wet finger.
Test the strength of the small 5 X 10 X 1.5 cm bricks.
Support the two ends of the brick on the edges of two tables.
Load the middle of the test brick with weights or attach a bucket into which sand can be poured.
Keep loading until the test brick breaks.
Suspend the weights and bucket near the floor so that they have almost no distance to fall.

3.67 Tests for strength of plaster of Paris bricks
See diagram 3.65: Test the strength of a brick
Plaster of Paris is partially dehydrated calcium sulfate crystals, CaSO4.H2O, made by heating gypsum.
When mixed into a paste with water it sets quickly and expands.
It is used as a fine casting material.
Put 4 mL of water into a beaker.
Add the powdered plaster of Paris slowly with a spatula.
Continue adding the plaster until it just appears above the surface of the water.
The plaster absorbs the water and you should finish with a very thin layer of water, about 1 mm, above the plaster.
Stir the mixture well.
When it begins to thicken, pour it into the paper box.
Smooth the surface of the cement in the mould and leave to set for 1 day.
Test the surface and strength of these bricks.
Plaster of Paris is not often used as a construction material, but calcium sulfate as gypsum, CaSO4.2H2O, is used to prepare
Portland cement.

3.68 Putty
Make putty (glazier's putty, painter's putty), with calcium carbonate paste (whiting), + linseed oil (+ white lead).
Putty is used as a, filler in glazing, to seal glass into frames.

34.2.1 Heat treatment of needles
Heating steel material to "red heat" then cooling it slowly is called annealing.
Putting steel material heated to red heat into cold liquid to cool it quickly is called quenching.
Reheated steel material is quenched to the temperature slightly lower than "red heat" temperature, then cooled slowly, called tempering.
Annealing, quenching and tempering are heat treatings to change rigidity, brittleness and toughness, by changing the arrangement of iron
Annealing is a form of heat treatment to soften a metal and make it easier to work.
Annealing is often used to soften steel to relax its inner stress to change its shape by forging, pressing and machining.
Obtain some sewing needles about four to 5 cm long.
These needles are alloys of iron and carbon, but the proportion of carbon is very small.
Try bending a needle.
It is tough and springy.
These properties of this carbon steel are dependent on the arrangement of the carbon atoms among the iron atoms.
The effect of annealing, quenching and tempering is to alter this arrangement in a specific way. Heat treatment of razor blades or steel knitting needles
The properties of steel whether it is hard, tough, springy depend on the manner in which the steel has been treated previously and, in
particular, on how it has been heated or cooled.

1. Hold one end of a razor blade in a pair of pliers and try to bend the other with a pair of pincers.
The blade snaps because it is brittle, although the steel is extremely hard.

2. Hold one corner of a razor blade in a pair of pliers and heat it strongly over a Bunsen burner flame until it is red hot.
When it has been red hot for half a minute make the flame gradually less hot and smaller, so that the blade cools down very slowly.
The gradual cooling should occupy at least five minutes.
When the blade is cold it is found to have lost its hard and brittle character.
It can now be bent easily without breaking, and it stays bent.
This process of slow cooling is called "annealing" the steel.

3. Straighten the blade used in the foregoing experiment, and once more heat it until it is red hot.
Have available cold water in an old cup or mug.
When the blade has been red hot for a short time put it into the cold water.
The rapid cooling in this treatment makes the blade hard and brittle.

4. Dry the blade after the quick cooling in the previous experiment.
Rub it with emery paper until the surface is bright and clean.
Holding the corner of the blade in the pliers.
Heat it by holding it an inch above a medium Bunsen burner flame until a blue sheen just appears over the surface.
Let the blade cool.
It is now strong and springy.
This moderate heating followed by cooling is called "tempering" the steel.

34.2.2 Annealing
1. Heat a needle to bright red heat.
Hold it vertically in the flame and then very slowly raise it out of the flame taking about one minute.
When it is cool, try bending it.
It should be soft and easily bent round a pencil.

2. Use pliers to clamp a needle's tail and forcibly insert a needle into the hard block then try to bend the needle.
You may find it is very difficult because the needle has strong rigidity and toughness.
Now use the pliers to clamp its tail and place it on an alcohol burner to heat.
About one minute later, its most part changes dark red.
Lay it aside to cool slowly.
When its temperature lowers to the room temperature, insert it into the block.
You may find that it is easy to bend it.

34.2.3 Quenching
1. Neither the soft needle nor the brittle needle is very useful.
However, the tough springy form can be restored.
Heat and quench a needle as before to obtain the hard, brittle form.
Carefully clean and shine the surface with emery cloth.
The needle must now be heated very gently until a deep blue oxide film appears on the surface.
This colour is an indication of the temperature at which the needle is tempered.
When the needle is cool, try bending it.
Is it tough and springy like the original needles?

2. Heat a needle to bright red heat and, while it is still hot, plunge it completely into cold water.
Try to bend it now.
It should be brittle and easily broken into small pieces.

3. Use the pliers to clamp the tail of another needle and heat it on an alcohol to dark red.
Place it into cold water at a beaker to cool it quickly.
Insert it into the block then bend it.
You may find that it becomes very hard but brittle and easy to break.

34.2.4 Tempering
Polish the needle quenched at Test B with the sand paper then reheat it on the alcohol burner.
When it becomes blue black, take it from the burner and lay it aside to cool slowly.
When its temperature lowers to the room temperature, insert it into the block to bead it.
You may find that it becomes tough.

34.3.0 Materials from the Earth, cement
1.0 Types of materials:
1.1 solid, liquid, gas, plasma,
1.2 crystals, fibres, fabrics, plastics, wood,
1.3 metals, non-metals,
1.4 polymers, acids/bases,
1.5 building materials
2.0 Properties of materials:
2.1 taste, odour, colour,
2.2 lustre, texture, acoustic
3.0 Characteristics:
3.1 absorbent, porous,
3.2 transparent, translucent, opaque,
3.3 magnetic, non-magnetic,
3.4 density light / heavy, floats / sinks,
3.5 solubility,
3.6 strength, hardness, flexibility,
3.7 viscosity,
3.8 conduction / insulation,
3.9 heat / electricity reactivity with other substances.

1. Natural materials
1.1 Organic:
1.1.1 plants: wood, fibres,
1.1.2 animals: wool, leather, glue
2. Inorganic rocks, ores, minerals
2. Processed materials: metals, alloys, plastics, salts, synthetic fibres, paper, glass, brick, cement
3. Uses: building, tools, clothing, food, cleaning, medicine, recreation
4. Changes made to properties of materials to meet required uses.

34.3.1 Lime (quicklime and slaked lime)
The word "lime" is commonly used for both quicklime and slaked lime, and for convenience we shall consider the substances together.
Quicklime is manufactured by roasting chalk or limestone in a lime kiln.
It has the property of giving out a brilliant light when strongly heated, and fifty years ago was used for lighting stages (hence the phrase
"to be in the limelight").
Slaked lime, or calcium hydroxide, is made from quicklime by adding water to the latter.
This process is called "slaking" the quicklime.
Slaked lime is used to make lime water and mortar.
It is also used by gardeners to "sweeten" the soil, i.e. increase the pH.

34.3.2 Prepare quicklime
Quicklime: CaO
Use a lump of marble, chalk (not blackboard chalk), or limestone twice the size of a thimble, and 20 cm of iron wire.
Copper wire is not suitable, because it melts with the heat.
The wire used for tying up bundles of firewood answers the purpose.
Tie one end of the wire round the lump and hold the other end in a pair of pliers or fasten it in a metal stand.
Put a sheet of asbestos or a metal tray below the Bunsen burner in case the lump falls out of the wire.
Suspend the lump just inside a very hot flame and heat it for ten to fifteen minutes.
In a short time the lump begins to glow as quicklime forms.
After heating let the lump to cool on the asbestos or metal tray.
Test the quicklime as described in the next experiment.
Another method of making quicklime is to put the lump of marble, chalk or limestone into a glowing fire with a pair of tongs
and leave it there for twenty minutes.
Quicklime can also be made from powdered chalk with the help of a home-made blowpipe, as described.
The making of quicklime from marble, chalk, or limestone is represented by the following chemical action:
CaCO3 --> CaO + CO2
Calcium carbonate -> calcium oxide + carbon dioxide.

34.3.3 Prepare quicklime by slaking
Put small lumps of fresh quicklime into an evaporating dish or watch glass.
Use a test-tube to add drops of water.
Clouds of steam arise, accompanied by a hissing noise.
The water may boil.
Finally, the solid breaks up into a fine, dry powder.
The water has combined chemically with the quicklime, and slaked lime remains.
The word "quick" in quicklime means "live", as in "the quick and the dead" and "quicksands".
The superstitious people of the middle ages believed that quicklime was inhabited by a "spirit".
When water was added to quicklime the "spirit" was released and a "dead" substance remained.
To this day, slaked lime is often called "killed lime".
Making slaked lime
CaO + H2O -->Ca(OH)2

34.5.0 Mechanical properties of materials, elastic, ductile, malleable
See diagram 34.5.0: Strength of materials, three bars
In the diagram, the three bars were originally all the same length.
They demonstrate the concepts of stress, strain, Poisson's ratio and the strength of a material.
Stress: force per unit area
Strain: deformation produced by stress
Poisson's ratio: the ratio of the proportional decrease in a lateral measurement to the proportional increase in length of a stretched

1. Elastic
If forces are applied to a body remaining in equilibrium, the length volume or shape alters temporarily or permanently, i.e. it becomes
If the forces applied to the body stop and the body regains its original length, volume and shape, then the deformation occurred within
the elastic limit of the body.
The magnitude of the elasticity of the body or the material comprising the body is expressed as a modulus of elasticity.

2. Ductile
Ductility is the ability of metals or alloys to keep their strength and be permanently distorted and not crack or fracture, when their
shape is altered.
Some ductile metals, e.g. copper, can be drawn through a die to reduce the cross-section by plastic flow and form wire, but other
metals lose their strength and crack.
Gold is among the most ductile metals.
One gram of gold can be drawn into a wire 2 km long.
The atoms of a ductile metal can slide past each other without causing the material to break into pieces.
Also, a ductile metal can be hammered so finely that light can pass through it.
Only metals are ductile.

3. Malleable
A malleable metal can be hammered, pressed or extruded out of the original shape, and not tend to return to the original shape or to
fracture or break.
Both ductile and malleable metals or alloys have large crystals.
Metals have a regular pattern of fixed particles consisting of the nucleus of an atom and inner electrons around the atom.
Outer electrons (delocalized electrons, valence electrons) are held only loosely by the nuclei of the atoms, so they can mover freely
between the fixed particles allowing metals to have good heat conductivity and good electrical conductivity.
Metals are malleable and ductile because distorting metallic crystals doe not completely break all the metallic bonds.
Many metals have high melting points and high boiling points because their chemical bonds are strong.
The greater the number of outer shell valence electrons the higher the boiling point.

34.5.01 Elasticity (Stress: tension, compression, shear)
See: Hooke's law, Tensile test machine, (Commercial)
See: Mechanics Structures Tester, stress and strain, (Commercial)
"Balloon Racer", use elastic potential energy to power a racing car (toy product).

See 35.20: Tenacity (Geology)
See diagram 34.5.0: Three types of stress, Hooke's law
Elastic materials strain when stretched and quickly return to their original state once the stress is removed, usually caused by bond
stretching along crystallographic planes in an ordered solid.

The three types of stress
1. Tension
Equal and opposite forces acting away from each other along the same line of action that tend to elongate the body
2. Compression
Equal and opposite forces acting away towards each other along the same line of action that tend to shorten the body.
3. Shear
Equal and opposite forces acting along different lines of action that tend to twist the body without changing its volume.
The amount of deformation is proportional to the applied stress only until the applied stress reaches the elastic limit.
Within the elastic limit when the deforming force is removed the body returns to its original shape and volume.
At some stage applied stress beyond the elastic limit the body can no longer be deformed and so it breaks.
For example, stretch springs of copper and brass.
The copper spring remains extended because it has reached its elastic limit.
Shearing causes shear strain, where parallel surfaces slide past one another, occurs when forces are applied to shears and scissors.

34.5.02 Viscoelasticity, creep
Viscoelastic materials show viscous and elastic characteristics when deformed.
They have the relationship between stress and strain depending on time.
All materials have some viscoelastic response.
For example, the behaviour of steel or aluminium, at room temperature and under small strain, does not deviate much from linear
Viscoelastic effects occur in synthetic polymer foams, polystyrene, guitar strings, tuning forks, wood, metals at high temperature,
shoe insoles, human tissue, e.g. spinal discs, skin.
For example, if skin is pinched, the harder the pinch the longer it takes to return to its normal position.
Creep is a slow, progressive deformation of a material under constant stress.

The behaviour of viscoelastic materials include the following:
1. If the stress is held constant, the strain increases with time, viscoelastic creep.
2. If the strain is held constant, the stress decreases with time, viscoelastic relaxation.
3. The effective stiffness depends on the rate of application of the load.
4. If cyclic loading is applied, hysteresis, a phase lag, occurs, leading to a dissipation of mechanical energy.
5. Acoustic waves experience attenuation.
6. Rebound of an object following an impact is less than 100%.
7. During rolling, frictional resistance occurs.

34.5.03 Bulk modulus, modulus of incompressibility, K
Compressive stress / Volumetric strain =
Deformed force per unit area / Change in volume per unit volume = K.
so K = (F/A) / (change in volume v / original volume V) = PV /v = K
[Compressibility = 1/K].
Unlike gases, liquids and solids have little space between the particles so are difficult to compress.
Solids are more difficult to compress than liquids.
Some bulk modulus approximate values: steel 160 GPa, glass 35 -55 GPa, water 2.2 GPa (so water is not completely incompressible!).

34.5.04 Young's modulus, E, elasticity, stress and strain
See: Strain (Commercial)
See diagram 35 5.04: Young's modulus
Strain is a force tending to pull a something apart, or push a something against a resistance, or alter the shape of something.
Young's modulus describes the proportional deformation produced in something by the application of a stress.
Strain has no dimensions.
Stress is the pressure or tension exerted on something that tends to deform it.
Stress is measured in units of pressure.
(Linear stress / Linear strain) = (Deforming force per unit area / Change in length per unit area) =
(F/A) / (increase in length e / original length L) = FL/eA = E
The SI unit of Young's modulus is the pascal, Pa.
However, in practice, the common unit is gigapascals, GPa, i.e. kN / mm2.
(In USA, pounds force per square inch (PSI), but in practice ksi, i.e. thousands of pascals per square inch.).

Some Young's modulus values: steel 200 GPa, glass 65 GPa, aluminium 70 GPa, polystyrene 3 GPa.
The Young's modulus values of different types of chemical bonds can be measured:
Covalent bonds, e.g. C-C bonds, 200-1000 GPa,
Metallic bonds, e.g. all metals, 60-300 GPa,
Ionic bonds, e.g. Alumina, Al2O3, 32-96 GPa,
Hydrogen bonds, e.g. Polyethylene, 2-12 GPa,
Van der Wall's bonds, e.g. waxes, 1-4 GPa.

34.5.04a Experiments
1. To show that stress is proportional to strain in a wire under load.
Suspend two wires of the same material, parallel from the same support.
The scale on the first wire is kept taut an attached weight.
Extend the second wire with different loads and measure the extension with a vernier scale attached to the first wire.
Measure the unextended length and the diameter of the wire with a rule and a micrometer.
Calculate Young's modulus from the gradient of the graph and the measured data
2. Design an experiment to collect data to determine the following for a chosen piece of confectionery: Proportional limit, Elastic limit,
Yield point, Fracture, Young's Modulus.

34.5.05 Shear modulus, modulus of rigidity, G
See diagram 34.5.05: Modulus of rigidity apparatus
1. Shearing stress /Shear strain = (F/A) / change in an angle of π/2 radians (90oC)
If forces are applied tangentially to the upper and lower surfaces of a cube causing the shape to change without change in volume,
section of the cube at right angles to those two faces will have their angles changed from π/2 to (π/2 + θ) or (π/2 - θ).
Young's modulus is related to shear modulus, G, Poisson's ratio v, and bulk modulus, K, by the formula:
E = 2G(1+ v) = 3K(1-2v) = 9KG / (3K + G).

2. The apparatus consists of a rod clamped at one end and attached to a wheel at the other.
The rod passes through a bearing at the wheel end and known torque may be applied by a string wrapped around the wheel.
The twist in the rod is measured with an angular scale.

3. Solids have modulus K, modulus E and modulus G.
Liquids have modulus E and modulus K only.
Gases have modulus K only.
Some shear modulus values at room temperature:
steel 79 GPa,
glass 26 GPa,
aluminium 25 GPa,
polyethylene 0.117 GPa.

34.5.06 Poisson's ratio, v
A longitudinal pull in one direction produces an extension in that direction and a contraction at right angles to that direction.
the stretched body becomes thinner.
The ratio of the lateral contraction per unit breadth to the longitudinal extension per unit length in the line of the applied force is the
Poisson's ratio for the material., v.
Stretch a rubber hose to show lateral contraction with increasing length.
Use a two dimensional spring model to show Poisson contraction in crystals. Hooke's Law, elastic limit, deforming force, stress and strain
See: Hooke's law, (Commercial).

| See diagram 34.5.1: Young's modulus
| See diagram 34 5.1.1: Hooke's law, spring
Materials that recover their original shape after an applied force is removed, show elastic deformation.
Materials that do not recover their original shape after an applied force is removed, show plastic deformation, because the applied force
was greater than the elastic limit.
Stress is the applied force per unit area of a material.
Stress may cause a strain.
Strain is the change in dimensions of a material / original dimensions of the material, e.g. change in volume per unit volume.
Hooke's law states that, within the elastic limit, the stress is proportional to the strain.
The constant of proportionality, elastic constant, for a material is called Young's modulus, E.
With wires made of iron or annealed steels, at the elastic limit (yield point), a sudden plastic deformation occurs.
The wire "gives" and despite decrease of stress the wire does not return to its previous shorter length.
Hooke's law does not apply to polymers or rubber.
When a small stress results in a big strain, the material is soft.
When a big stress results in a small strain, the material is hard.
When a small stress results in permanent deformation, the material is plastic.
A modulus is a numerical quantity representing some quality of a substance equal to the ratio of the magnitude of the cause to the
magnitude of its effect on the substance.
The bulk modulus of a material is often expressed for convenience in GPa, gigapascals.
1 gigapascal = 1000000000 pascal, 109 pa.

1. Mark the beginning and end positions of several different masses.
Compare the end positions of masses that are multiples, such as double or triple.

2. With the spring held in the pin vice on the stand, weights are added in steps of 1 kg.
The greater the weight added, the greater the extension of the spring and the relation between them should be linear in nature
according to Hooke's Law.
Releasing the weights should see a return to the original extension.
When this is occurring the spring is displaying elastic deformation.
If enough weight is added to the spring, it will deform permanently and lose its elasticity.
This is known as plastic deformation.
It is interesting to note that if the experiment is repeated with rubber bands, Hooke's Law is not followed.
Rubber is extremely non-linear in its stress-strain characteristics.

3. Pull on a horizontal spring with a spring scale.
Use 2 metres of copper wire, e.g. 32 SWG, stretched by weights attached to the end the wire through a pulley.
Plot a graph of load against extension of the wire.
The graph is a straight line to show that Hooke's law applies, extension is proportional to stretching force.
Take off weights and observe that the wire returns to its previous lengths at the same tensions.

4. Repeat the experiment by adding weights until the wire suddenly "gives" or "runs".
This is called the yield point.
The wire has stretch proportionally much more than previously for the load added.
The wire can support heavier loads.
However, when the weights are removed, the wire can no longer return to its original lengths.
At the yield point the wire had reached its elastic limit and Hooke's law no longer applies.
In engineering, metal components should carry loads only within their elastic limits. Stretch springs
Add masses to a pan balance and measure the deflection with a vernier scale or cathetometer (travelling microscope).
Examine the force / displacement curve at small extensions.
Add 10, 20 and 30 newton to a large spring. Strain gauge
Pull to various lengths a spring attached to a dynamic force transducer and show the resulting force on a voltmeter. Ductility and elongation of metal
Use pieces or iron wire and copper wire.
Beat the wire flat with a hammer to make them thinner.
Note the thickness at which they break.
Repeat the experiment with folded zinc and lead sheet. Young's modulus of students
Dr Richard Walding collected the following data in a Brisbane high school using Year 7 girls
Aim: To measure the body lengths lying on the floor and standing upright to see the effect of gravity.
The average shrinkage when standing was 2.4 cm.
Class averages:
Length lying 161.2 cm
Length standing 158.8 cm
Delta L = 2.4 cm
Waist circumference 65.8 cm
Mass 37.2 kg
Force (weight) 365 N
Cross sectional area = 0.034 sq m
Tensile strength (F/A) = 10621pa
Pa Strain (delta L/L) = 0.0152
Young's Modulus = 0.700 MPa
(Young's Modulus for biological tissue = 0.2 MPa). Breaking strains, brittleness
A material distorted by forces acting on it is in a state of strain, is strained.
So strain is the ratio: change in dimension / original dimension., and has no units.
Direct tensile or compressive strain = elongation or contraction / original length.
Shear strain causes a rectangle to become a parallelogram.
Volumetric strain, bulk strain = change in volume / original volume.
Approximate breaking strain in kg of some metals and wires hard drawn through the same gauge (No. 23):
Copper, breaking strain 12 kg,
Tin, breaking strain < 3 kg,
Lead, breaking strain < 3 kg,
Tin-lead (20% lead) 3 kg,
Tin-copper (12% copper) 3 kg,
Copper-tin (12% tin) 40 kg,
Gold (12% tin) 9 kg,
Gold-copper (8.4% copper) 32 kg,
Silver (8.4% copper) 20 kg,
Platinum (8.4% copper) 20 kg,
Silver-platinum (30% platinum) 34 kg.

However, the malleability, ductility, and power of resisting oxygen of alloys is generally diminished.
The alloy formed of two brittle metals is always brittle.
The alloys formed of metals having different fusing points are usually malleable while cold and brittle while hot.
The action of the air on alloys is generally less than on their simple metals, unless the former are heated.
A mixture of 1 part of tin and 3 parts of lead is scarcely acted on at common temperatures, but at a red heat it readily takes fire, and
continues to burn for some time.
Similarly, a mixture of tin and zinc, when strongly heated, rapidly decomposes both moist air and steam.
Brittleness is the tendency for metals or alloys to have a brittle fracture when under tension, without plastic deformation, i.e. still
keeping its shape.
Brittleness mean a low value of fracture toughness, toughness.
Brittle fracture is causes by cracks leading to more cracks usually along certain crystal planes. Breaking threads
1. Place a broom handle across two stools.
Attach a thread to be tested to the centre of the broom handle.
Attach the lower end of the thread to a large plastic bottle.
Add water to the jar until the thread breaks.
Note the volume of water needed to break the thread.

2. Add heavy masses to different threads until they break, e.g. cotton thread, thin copper wire, fishing line, dental floss, wool yarn,
catgut, piano wire.
Compare the breaking strain of the fishing line with this information on the packet. Breaking spaghetti
Hold each end of a length of dry spaghetti with two hands.
Bring the hands together to bend the spaghetti until it snaps.
The spaghetti always breaks into more than two pieces, usually three pieces.
The spaghetti breaks when when the amount of curvature approaches a critical value called the rupture curvature.
The broken ends straighten sending waves of curvature back towards the hand which, in spaghetti can interact to cause another break. Shear strength of thin sheets
See diagram Clothes-peg tester
Cut sheets of material to be tested so that they just fit around a spring clothes peg, e.g. newspaper, paper towel, potato chip packet,
thin plastic, cling film.
All the sheets should have the same shape and area.
Wrap each sheet around the spring clothes peg and squeeze the ends of the clothes peg handles with the thumb and first finger.
Note which materials stretch or break. Bend beams, bend metre stick, stress rectangular bar, different woods
Hang 2 kg from the centre of a metre stick supported at the ends.
Place the metre stick on edge and then on the flat bending beam.
Load a rectangular cross-section bar in the middle while resting on narrow and broad faces.
Hang weights at the ends of extended beams.
Use beams of different lengths and cross sections.
Use different woods. Sagging board, aluminium / steel elasticity paradox
Show that copper and brass rods sag by different amounts under their own weight but steel and aluminium do not. Stretch a hole, deformation under stress, stress on a brass ring
See 2.05: Conic sections, ellipse
Stretch holes arranged a circle in a rubber sheet to deform into an ellipse.
Paint a pattern on a sheet of rubber and deform by pulling on opposite sides.
Use a strain gauge bridge to measure the forces required to deform a brass ring. Squeeze the bottle
Fit a bottle with a stopper and a small bore tube.
Squeeze the bottle and watch the coloured water rise in the tube. Prince Rupert's Drops, tempered glass, toughened glass
Bubbles made by dropping molten glass into water.
The shape is like that of a tadpole.
If the smallest portion of the end of the tail is nipped off, the whole bubble explodes into fine dust.
This novelty was introduced into England by Prince Rupert (1619-682), grandson of James I.
He also introduced Prince Rupert's metal, an alloy of brass.
Cool a drop of molten glass very quickly.
Hit the round bulb of the glass with a hammer.
It does not break.
Break off the sharp tip of the drop.
The glass shatters.
This phenomenon is a form of tempered glass (toughened glass) that are manufactured into sheets that break into small granular chunks
instead of dangerous pointed shards.
The sheets are used in buildings, telephone box windows and the side windows of cars.
Car windscreens are made of laminated toughened glass.
Another method of producing toughened glass for complex shapes, e.g. drinking glasses, involves treating glass in molten potassium
For sale:
Tumbler, toughened glass, 230 mL, pack / 6. Tennis balls
Use tennis balls to protect from sharp corners of furniture, grip strengthener, rolling foot massage, back massager, hit distant cobwebs,
prevent sleeping on your back, prevent chairs slipping. Coffee, coffee tins
Use coffee to dye fabric brown, fertilize houseplants, repair scratched woodwork, deter ants.
Use coffee tins to spread grass seed, protect baby tomato plants, raise melons off the ground, start a charcoal fire, demonstrate
atmospheric pressure and expansion of heated gases. Lip balm
Use lip balm as protectant and lubricant on skin, skin cuts, car battery terminals, zippers, ring fingers, nails and screws, facial hair,
leather shoes, furniture drawers and windows. Nail polish
Use nail polish to stop cut fabric from fraying and runs in nylons, repair cracks in glass or plastic or wooden floor, prevent rust on
screws and bottom edges of cans, thread needles, protect shiny surfaces, shirt buttons, prescription labels.
Acetone was formerly know as "nail polish remover". Toothpaste
Use toothpaste (old fashioned white toothpaste not modern gel toothpaste) to polish silverware, clean small white objects, remove ink
spots, treat facial pimples.
Remove crayon marks, scratches on glass or shoes, clean hands, faces and feet, baby bottles, fill small holes in walls. Toothpicks
Use toothpicks to apply glue, plug holes, draw designs in sand, suspend seed potato in water, repair eyeglass lugs, mark starting point
of a tape roll, clean tight spaces, small plant splints, turn sausages, tighten a loose screw, push fabrics through pressure foot of a sewing
machine, test whether cake is baked. Shear stress
See: Mechanics Structures Tester, stress and strain, (Commercial)
Shear is a kind of deformation of materials where parallel plates of the material are displaced in a direction parallel to themselves, but
the parallel plates remain parallel.
So the adjacent planes of parallel plates slide over each other.
If a shearing force is applied parallel to one side of a rectangle it becomes a parallelogram.
Shear stress is the applied force divided by the area of the material parallel to the applied force, i.e. F / 1.
Use scissors to cut 1. a sheet of paper, 2. tough plastic tube.
The paper is cut sharply but the plastic tube stretches between the blades of the scissors. Shear book, foam block
Use a very thick book or stacks of cards to show shear.
Push on the top of a large book or a large foam block to show shear. Plywood sheets, shear torsion
Use a stack of plywood sheets with springs at the corners to show shear torsion bending. Torsion rod, modulus of rigidity, bending and twisting
Twist a rod by a mass hanging off the edge of a wheel.
Wind a copper strip around a rod and then remove the rod and pull the strip straight to show twisting bending and twisting.
Twist rods of various materials and diameters in a torsion lathe.
Grab each end of a plastic ruler and twist the ends in opposite directions.

34.6.2 Test the strength of a simple bridge
See diagram 34.6.2: Simple beam bridge
1. Use C-clamps and blocks of wood to fix one piece of knotless wood (lathe), e.g. 0.5 cm × 5 cm × 60 cm, with the wider width
(5 cm) down (flat board), between two tables 0.5 m apart.
Use rope to attach an empty bucket to the centre of the bridge.
Add sand to the empty bucket until the wood bends downward 1 cm at the centre.
Weigh the bucket and sand.
Add sand until the wood breaks.
If the wood does not break just use the data: Weight to bend down 1 cm.

2. Repeat the experiment decreasing and increasing the distance between the two tables to find the weight needed to bend the wood
downward 1 cm and the weight to break the wood.
All the pieces of wood must be free of knots.
3. Repeat the experiment with the narrower width (0.5 cm) down (vertical board).
4. Drill two holes vertically in the board and repeat the above experiments.
Table 34.6.2
Distance between tables Weight to bend down 1 cm Weight to break wood
50 cm .
55 cm .
45 cm .

34.6.3 Strength of paper, shape and its mechanical strength
See diagram 34.3.1: Folded paper, crossbeams
A flat piece of paper placed over two rods can support only light weight.
However, if the piece of paper is folded into many alternate ditches and edges it can support heavier weight.
Draw parallel lines on A4 paper 1 cm apart.
Fold the paper alternately each way along the parallel lines.
Cut out a 4 cm square of cardboard and put it on folded paper.
Add weights to the cardboard or put an empty glass on it and add water until the paper begin to change its shape.
Repeat the experiment with paper folds 0.5 cm apart and 2.0 cm apart.
Compare the results of the two experiments.
Crossbeams made of reinforced concrete are used in building construction as in diagram 34.3.1.(b), not as in diagram 34.3.1.

34.7.1 Bouncing balls, Silly putty, silicone, bouncing putty, "Tricky Putty"
Drop balls of different material on plates of various materials.
Observe loss of mechanical energy in the coefficient of restitution.
Drop balls on a glass plate.
Drop glass, steel, rubber, brass, and lead balls onto a steel plate.
Drop rubber balls of differing elasticity and silly putty on a steel plate.
Observe variation in coefficient of restitution n baseballs.
(Dow Corning 3179 dilatant compound).

34.7.2 Coefficient of restitution (coefficient of elasticity)
See diagram 34.7.2: Bounce and no-bounce balls
If a ball mass m is dropped from height h1 and rebounds to height h2, the loss of energy = mg(h1-h2).
The energy loss is expressed as the coefficient of restitution, e = v2/v1 = sqrt h2/h1, where v1 is the incident speed and v2 is the
rebound speed
1. Drop bounce and no-bounce balls.
Measure the height the bouncing ball is dropped from, and the height it bounces to, and calculate the coefficient of restitution.
The sad ball will not bounce as it is made from energy absorbing material.

2. Newton found experimentally that if two smooth spheres collide with velocities u1 and u2 and rebound with velocities v1 and v2,
then - (v2 - v1) / (u2 - u1) is a positive constant, e, independent of the initial velocities, called the coefficient of elasticity or coefficient
off restitution.
The value of the constant e depends on the substances, e.g. 0.9 for glass and 0.2 for lead.

3. The coefficient of restitution can be used to measure of the elasticity of the collision between ball and racquet.
Elasticity is a measure of bounce, i.e. how much of the kinetic energy of the colliding objects remains after the collision.
With an inelastic collision, some kinetic energy is transformed into deformation of the material, heat, sound, and not available for
For a perfectly elastic collision, coefficient of restitution = 1, e.g. two diamonds colliding.
For a perfectly plastic, i.e. inelastic, collision, coefficient of restitution = 1, e.g. two lumps of Plasticine (modelling clay) that do not
bounce but stick together.
The coefficient of restitution = difference in velocities of two colliding objects after the collision / difference in velocities of two colliding
objects after the collision.
For a racquet and ball, v1 = velocity racquet centre before impact, s1 = velocity ball before impact, v2 = velocity racquet centre
after impact, s2 = velocity ball after impact
Coefficient of Restitution = (s2 - v2) / (v1 - s1)
For a falling object bouncing off the floor, coefficient of restitution = (bounce height / drop height), e.g. for a particular bouncing ball,
coefficient of restitution = 0.85.

34.7.3 Dead and live balls
Drop a black super ball and a ball rolled from a piece of wax.
Make a non-bounce ball by filling a hollow sphere with iron filings or tungsten powder.

34.8.2 Ice model
Make ball and stick water molecules that you can stick together to make ice.

34.8.4 Ice nuclei
Let large ice crystals form on the surface of a super cooled saturated sugar solution.

34.8.5 Crystal growth in a film
Observe crystal growth on a freezing soap film through crossed Polaroid.

34.8.6 Crystal faults, crushing salt
Arrange one layer of small ball bearings between two Lucite (Perspex), sides.
Examine natural faults in a calcite crystal then the single layer of small spheres model faults.
Crush a large salt crystal in a big clamp.

34.8.7 Shape memory alloy, Nitinol
"Nitinol Memory Wire", Ni Ti alloys, shape memory alloy (toy product).

Convert thermal energy into mechanical energy with a shape memory alloy, Nitinol.
The thermobile consists of a shape memory alloy Nitinol (Nickel-Titanium).
Above a certain temperature, Tc, this alloy returns to an earlier shape given it by previous heat treatment.
The alloy absorbs heat as it returns to this shape converting it into mechanical work.
Dip the small metal wheel of the thermobile into hot water to raise the temperature of the alloy above Tc and rotation follows.

34.8.8 Solid models, sphere packing
Use tetrahedral and octahedral building blocks construct crystal shapes.
Use Styrofoam balls and steel ball bearings to make crystal models.
Stack balls on vertical rods mounted on a board to build crystal models.
Build crystal models with a combination of compression and tension springs.
Use old tennis balls glued together to show close-packed crystals.
Examine lattice models of sodium chloride, calcium carbonate, graphite and diamond.

34.9.1 Pollution from noise, noise effects thinking and learning, white noise
Often people use the word "sound" for something they want to hear, and "noise" for what they do not want to hear.
In general, musical sounds are made up of a certain limited number of frequencies.
They are regarded as sounds even though some people may not want to hear them.
Motor traffic, aircraft and trains all produce a complex range of sounds of many unrelated frequencies at the same time.
This is described as noise.
It is a random mixture of sounds of different frequencies and amplitudes.
Study the reasons causing noise and the ways lowering noise.

34.9.2 Noise sources, test A
Use a knock-down [be able to be dismantled] transformer.
Install its primary coil and secondary coil well and let its iron core in not closed state (viz. do not install the upper iron frame).
Turn on the AC electrical source for the primary coil and observe the vibration and sound of the iron core.
Make the iron core closed but do not screw the screws tightly and note the change in sound.
Screw the screws tightly.
You may find noise lowers observably.
Many noises are caused by disordered vibration of some components without being fixed well.
Be careful not to touch the metal parts of the transformer because it carries AC of more than 36V.
Place a plastic ruler on a tabletop flat and let it spread 1/3 long out of the table and vertical to the table rim.
Press the end at the table with your left hand and take a press on another one with your right to make the ruler vibrate.
Note the vibration on the tabletop and the noise it emits.
Place a large, thin, sponge pad under the ruler to separate the ruler and the table.
Repeat the above experiment.
You may hear only the sound the ruler vibrates.
Adding some elasticity materials under vibrating objects may lower vibration noise effectively because elasticity materials may absorb
vibration energy.

34.9.3 Noise control, test B
Use a small radio and a box Turn on the radio to the most volume.
Place the radio into the box then cover its cap.
Listen to the sound.
You may find the sound decreases slightly.
Separately put some cotton, sponge and broken stones in the space between the radio and box wall.
Listen to the sound again.
You may find cotton and sponge make the sound decrease more observably.
Actually many spongy materials are sound absorption materials.
If place them at the places transferring noise, they can lower noise effectively.

34.9.4 Pollution from light of buildings
Many modern buildings' outside walls are decorated with glass mirrors.
Thus there is much sunlight being reflected to fixed direction.
The inhabitants living at the places opposite to the buildings are under the strong light pollution.
For example, their rooms are hotter in summer, their children's eyesight lowers due to the strong light's stimulation.

To study how reflected sunlight makes the temperature at a small space increase in summer obtain two same large boxes.
For paper boxes, wrap a layer of thin heat insulation materials such as foam sponge and cotton pad to imitate the walls of a room.
Cut a window at a side of each box, making sure the two windows with the same size.
Shade the windows with transparent glass paper or plastic film.
Place the boxes in the sunlight in summer, but without sunlight shining in the boxes directly.
Insert a thermometer into each box.
Place a large mirror and adjust its position to make reflected sunlight into a box through its "window".
You may find the temperature at the box shined on by reflected sunlight increases quickly.
Carefully note the difference in temperature of the two "rooms" until the temperature at this box increases no longer.
Record the readings of the temperatures and calculate the difference in temperature between two boxes.
Remove the transparent glass paper shading each window to imitate "opening windows to air".
After a while, you may find the temperature at the box shined by reflected sunlight decreases more slowly than another box.
Carefully note the difference in temperature of the two "rooms" until the temperature at each box decreases no longer.
Record the readings of the temperatures and calculate the difference in temperature between two boxes.

34.9.5 Electrostatic precipitation
See diagram: 34.4.3: Precipitators
To build a model to show the action of an electrostatic precipitator you need concentrated hydrochloric acid, concentrated ammonia
solution, gas jar or measuring cylinder, test-tubes, thin metal rod, glass and plastic tubing, stoppers, induction coil and leads, aquarium
pump and aluminium foil.
The aluminium foil making up the outer electrode should be in the form of a cylinder inside the walls of the jar, but if you want to see
what is happening inside, you may leave a space.
Turn on the pump.
Hydrogen chloride from the acid reacts with ammonia from the next test-tube to form a smoke of ammonium chloride.
Notice the amount of smoke emerging from the chimney.
Gradually increase the flow of air from the pump then turn on the induction coil to supply the high voltage.
Note any change in the smoke from the chimney.

35.4 Rocks and minerals, definitions, mineral classification and origin
Rocks or stones are any naturally occurring aggregate of one or more minerals and are classified by origin as follows:
Igneous rock formed by volcanic activity,
Sedimentary rock formed from sediments and,
Metamorphic rock formed mainly by heat and pressure on original rock.
Minerals were originally the substances obtained by mining, but, to a geologist, a mineral is a naturally occurring inorganic solid with a
certain chemical composition and physical properties, including an ordered internal structure.
A mineral has a definite chemical composition and may have a characteristic shape.
A rock is a composite of more than one mineral.
Pieces of the same rock might be composed of different minerals.
Some rocks are composed of elements, e.g. gold or silver, but most rocks are combinations of elements in minerals.
For example, the mineral quartz is a combination of the elements silicon and oxygen.

Use the following testing and descriptive techniques to identify minerals.
Mineral classification:
1. Elements,
2. Sulfides (selenides, tellurides, arsenides, antimonides, bimuthides),
3. Halides,
4. Oxides, hydroxides,
5. Nitrates, carbonates, borates,
6. Sulfates (chromates, molybdates, wolframates),
7. Phosphates, arsenates, vanadates,
8. Silicates,
9. Organic substances
Mineral origin:
1. Crystallization from magma, e.g. magnetite, mica, quartz,
2. Physical, chemical and biological changes caused by weathering, e.g. serpentine, malachite,
3. Sedimentary and evaporation processes, e.g. rock salt, calcite,
4. Biological accumulation of salts, e.g. limestone, pyrite.

35.5 Colour
The colour is an obvious physical property but it varies too much to be a reliable property for identification.
However, rock colour charts are available, usually based on the "Munsell colour chart".
The names of some colours come from the characteristic colour of minerals, e.g. emerald, ruby, azure, amethyst.
Quartz, calcite and rock salt are colourless if they do not contain impurities.
However, some pure minerals may have different colours, e.g. fluorspar, apatite and beryl.
The colour of some minerals may be changed by sunlight, artificial light, ultraviolet light, turning in the light, radioactivity, surface tarnish,
heat, and dyes.

35.6 Lustre (metallic lustre, non-metallic lustre)
The lustre is the appearance of the surface of a mineral in reflected light, depending on the reflection and refraction of light.
The lustre often distinguishes minerals from one another.
Minerals are divided into two great groups on the basis of their lustre.
One group is opaque and has a metallic lustre like that of a metal.
The other group may be opaque or transparent but does not have a metallic lustre.
Most of the ore minerals have a metallic or a sub-metallic lustre.
Others may be vitreous or glassy; resinous, like resin; pearly or silky.

Minerals may be:
1. Opaque and with a metallic lustre, like a metal, e.g. pyrite, galena,
2. Opaque or transparent but without a metallic lustre, subdivided as:
adamantine (diamond-like) lustre,
vitreous (glassy) lustre,
greasy oily) lustre,
dull lustre,
silky lustre, e.g. asbestos and,
pearly lustre (layered).
A gem with changeable lustre, chatoyancy, is called a cat's eye, e.g. chrysoberyl, a form of quartz.
The lustre of a diamond used in jewellery is called its "water".
So the best diamonds are called "diamonds of the first water".

35.7 Transparency (transparent, translucent, opaque, refraction)
Transparent minerals allow passage of light without much deviation or absorption, like a window glass.
You can read through a transparent mineral, e.g. quartz (rock crystal), rock salt, topaz.
Translucent minerals allow passage of some light, but not images, e.g. frosted glass used in bathrooms.
Translucent minerals may be a transparent mineral containing impurities or finely granular transparent minerals.
The minerals gypsum and mica may be translucent or opaque if finely granular but transparent if big crystals.
Opaque minerals allow no passage of light and have a metallic or dull lustre.
Each mineral has a characteristic refractive index.
An anisotrtopic crystal may split incident light to produce double refraction, e.g. calcite crystal.

35.8 Crystal systems, crystal habit, crystal form
See diagram 35.8.1: Orthogonal axes
See diagram 35.8.2
: Non-orthogonal axes, and 120o axes
See diagram 35.8.3: Tabular, prismatic, and pyramidal habit
See diagram 35.8 4: Crystal form of the seven crystal systems
Most minerals are crystalline.
The patterns of the internal atomic structures result in a definite external shape.
Some minerals are amorphous, non-crystalline.
However, silica, SiO2, may occur as quartz crystals, irregular sand grain crystals, fine grain chalcedony aggregate, and amorphous opal

Crystal habit refers to the relative width and length of the crystal faces, i.e. the development of the faces of a crystal.
Crystal habits include:
pyramidal habit, e.g. native sulfur,
columnar habit,
tabular habit (flat slab), e.g. mica,
acicular habit (needle-like),
fibrous habit,
lamellar habit (plate-like),
prismatic habit (elongated), e.g. most silicates.
A similar term, "crystal form", refers to the geometric shape of the crystal.

When looking at a crystal:
"axis a" is "front to back",
"axis b" is "right to left", and
"axis c" is "top to bottom".
Orthogonal axes are mutually at right angles, i.e. the cubic, tetragonal, and orthorhombic (rhombic) crystal systems.
Non-orthogonal axes have one or more axes not at right angles to the others, i.e. the monoclinic and triclinic crystal systems.
The hexagonal and trigonal crystal systems have three horizontal axes mutually at 120o and at right angles to the vertical, axis c.
Let α = angle between axis b and axis c, β = angle between axis a and axis c, and γ = angle between axis a and axis b.

The seven crystal systems and examples of crystal form (geometric shape of the crystal):
1. Cubic (isometric): a = b = c, and α = β = γ = 90o, e.g. galena, garnet, halite, fluorite, magnetite, pyrite, sphalerite, uraninite
2. Tetragonal: a = b not = c, and α = β = γ = 90o, e.g. cassiterite, chalcopyrite, rutile, scheelite, zircon
3. Orthorhombic: a not = b not = c, and α = β = γ = 90o, e.g. barytes, marcasite, olivine, stibnite, sulfur
4. Monoclinic: a not = b not = c, and α = γ = 90o not = beta, e.g. augite, gypsum, hornblende, micas, orthoclase feldspar, serpentine,
5. Triclinic: a = b = c, and α not = β not = γ e.g. axinite, plagioclase feldspar, rhodonite
6. Hexagonal: a = b not = c, and α = β = γ = 90o, e.g. apatite, beryl
7. Trigonal: a = b not = c, and α = β = γ not = 90o, e.g. ilmenite, tourmaline.

35.9 Cleavage, fracture, twin crystals, crystal faces
See diagram 35.9: Twin crystals, striations, cleavage
1. Cleavage, the tendency to split along certain definite planes, is a very useful distinguishing property that reflects the crystalline
structure of a mineral and which can be related to the packing together of its atomic constituents.
Minerals may cleave in one, two, three or more directions with various degrees of perfection.
A cleavage occurs when you can split a mineral in a plane parallel to a crystal face leaving a smooth flat surface along this planes.
Some minerals have only one cleavage direction, e.g. mica.
Other minerals may have two or more cleavages.
For example, galena has three cleavages.
The direction of cleavage may be indicated by fine cleavage rifts running along the planes of cleavage.
Some fine grain rocks have a cleavage, e.g. slate.

2. Fracture is any breakage or rupture other than a cleavage.
Some minerals break evenly, others have an uneven or jagged hackly fracture.
The fracture may feel even, uneven, jagged and conchoidal.
Conchoidal is the shell-like pattern seen on chipped glass.
The fractures are curved as often in quartz.

3. Twin crystals may occur in a regular way with internal angles consistently at more than 180o, e.g. fluorite, gypsum, cassiterite.
4. Crystal faces may have characteristic striations, e.g. pyrite, quartz and tourmaline.

35.10 Hardness, Mohs scale of hardness
Minerals differ greatly in hardness.
The hardness refers to the resistance of a mineral to scratching, scratch hardness.
The Mohs scale of hardness (Friedrich Mohs 1773 - 1839) has a range from 1 (softest) to 10 (hardest).
Hold a specimen of a mineral with forceps and try to scratch the following substances with it:
fingernail hardness 2.5,
piece of copper or copper coin hardness 3,
steel knife blade hardness 35.5,
window glass hardness 35.5 to 6.0,
steel file hardness 6,
diamond hardness 10.
American coins have hardness 2.5, but the old "Indian heads" penny has hardness 3.35.
Hardness 7 substances produce sparks when hit with steel.
When hardness testing with glass, do not hold the glass in the hand, but place it on a flat surface.

Mohs scale of hardness of minerals:
1. talc,
2. gypsum,
3. calcite,
4. fluorite,
5. apatite,
6. orthoclase feldspar,
7. quartz,
8. topaz,
9. corunum,
10. diamond.
The Mohs scale of hardness of gemstones:
topaz 7,
emerald 8,
sapphire 9,
ruby 9,
diamond 10.

This hardness test can be applied only to fresh unweathered specimens.
The columnar mineral kyanite is unusual because has hardness 4-4.5 vertically , but hardness 6-7 horizontally.
Fibrous and porous aggregates may have a deceptively lower harness because of the spaces between grains.
Determining the hardness of earthy minerals, fine grain minerals and needle-shaped fibrous minerals is almost impossible.
Engineers do not use Mohs scale.
They define harness as resistance to indentation by a tool tipped with a pyramid-shaped diamond.
The scales include "Vickers", "Rockwell" and "Knoop", in units of force (newton) / diameter2 of the indentation, at an angle of
For example, the Australian "kangaroo" $1 Aluminium Bronze coin blanks have Vickers hardness 80.

35.11 Relative density, r.d.
(formerly specific gravity)
The relative density, r.d., of a mineral is a number that expresses the ratio between its mass and the mass of an equal volume of water
at 4oC.
If a mineral has a relative density of 2, it means that a given specimen of that mineral has twice as much mass as the same volume of
Most common minerals have a relative density of 2.5 to 4.0.
The following substances have their densities expressed in g / cm3:
sulfur 2.0,
quartz 2.6,
calcite 2.7,
copper 8.9,
lead: 11.35.
Some ores are not uniform in density because they contain variable quantities of quartz, feldspar and other minerals, e.g. malachite,
cassiterite and cerussite.
Minerals less than 2.5, feel "light" and those more than 3.0, feel "heavy" for their relative size.
The relative density of a mineral of fixed composition is constant and its determination is frequently an important aid in identification of
the mineral.
To find accurately the relative density of a mineral, it must be pure and it must also be compact, with no cracks or cavities where
bubbles or films of air can exist.

35.12 Streak
The streak refers to the colour of the ground or powdered mineral and is sometimes a reliable test.
To see the streak, rub the mineral on a ceramic streak plate or building tile or unglazed porcelain to leave a coloured scratch.
Porcelain has Mohs scale hardness 6-6.5, so harder minerals will only leave a streak of white porcelain powder.
Grind the harder minerals to see the streak colour.
The colour of the streak may be different from the colour of the gross mineral in the ground.
Colourless and white minerals always have white streak.
Minerals with metallic lustre show the greatest difference between the true colour of the mineral and streak colour, e.g. black haematite
gives a red streak powder.
A mineral usually has a constant streak colour even if the colour of the mineral varies.
So streak is much more reliable quality than colour of the mineral.
The iron mineral haematite gives a brick red streak and limonite gives a yellow streak.

35.12.1 Touchstone, gold streak
Touchstone is a form of schist used to assay gold by comparing the streak of the sample to the streak of "touch needles" with known
gold content.

35.13 Hydrochloric acid test, effervescence
Cold, dilute hydrochloric acid or white vinegar (acetic acid, ethanoic acid) causes bubbles, effervescence, with sedimentary rocks
containing mostly carbonates, i.e. limestone, e.g. calcite CaCO3, dolomite Ca(CO3).Mg(CO3), witherite BaCO3,
malachite CuCO3Cu(OH)2.

35.14 Magnetism test
Note whether the powdered mineral is strongly or weakly attracted to a magnet, e.g. magnetite Fe3O4, attracts iron dust.
Haematite becomes magnetic when heated.
Palaeomagnetism is the study of the magnetic record in ancient rocks, e.g. changes and reversals in ancient magnetic fields of the Earth.

35.15 Odour and taste
Argillaceous rock
Some minerals have a characteristic odour when rubbed, e.g. arsenopyrite FeAsS, fluorite.
Sulfur has a distinctive odour and clay minerals have an "earthy" smell.
Minerals soluble in water have a characteristic taste.
Some people claim that the amalgam fillings in their teeth allow them to taste certain minerals.
A "metallic taste" in the mouth may be caused by antibiotics, drugs, oral diseases and even mercury poisoning.
Usually the metallic taste disappears within days.
Some common examples include the following:
1. Chalcanthite, sweet metallic taste and slightly poisonous, CuSO4.5H2O, it is a water-soluble sulfate
2. Epsomite, Epsom salts, bitter taste, MgSO4.7H2O, hydrated magnesium sulfate
3. Glauberite, bitter and salty taste, Na2Ca(SO4)2, sodium calcium sulfate
4. Halite, rock salt, saline taste, NaCl
5. Hanksite, salty taste, Na22K(SO4)9(CO3)2, sodium potassium sulfate carbonate
6. Melanterite, sweet, astringent and metallic taste, FeSO4.7H2O, hydrated iron sulfate, Sylvite (sylvine) bitter taste, KCl.

35.17 Grain size and roundness
Measure size and roundness with a sand gauge.
Size classification systems include the logarithmic "Wentworth scale" and the "USCS scale" (United Soil Classification System).
Grain sizes:
boulder > 256 mm,
cobble 64 to 256 mm,
pebble 4 to 64 mm,
gravel (granule) 2 to 4 mm,
sand 1/16 to 2 mm,
silt 1/256 to 1/16 mm,
clay < 1/256 mm.

35.18 Feel and conductivity
Experienced handlers of minerals, e.g. gemstone workers, claim to be able to recognize minerals from the feel against the fingers or the
For example they say that talc and graphite feel smooth and greasy, while kaolin (China clay) and chalk feel rough and dry.
Copper feels colder than amber against the cheek because copper is a better conductor of heat.
Similarly, they can distinguish real gemstones from glass imitations by feel against the cheek.

35.19 Shape or form
Minerals may be found in a number of different shapes.
They may be crystals, parts of crystals or groups of crystals, which may be just massive or grouped haphazardly or in a particular way.
If the crystals radiate from a point we may call them radiating.
They may form networks or be reticulated.
Tree-like or moss-like shapes are described as mossy or dentritic.
Many other descriptive terms are used to describe mineral aggregates.

35.20 Tenacity
Most minerals are brittle.
Minerals may be:
sectile (can be cut easily with a knife),
malleable (can be flattened out under a hammer),
flexible (can be bent without breaking,
elastic (resumes natural shape after expansion, contraction or distortion).

35.6.0 Geological time scales
Table 35.6.0 Australian Museum Geological Divisions (edited)
Time million years ago
> 545
545 - 490
490 - 434
434 - 410
410 - 354
354 - 298
298 - 251
251 - 205
205 - 141
141 - 65
65 - 55
55 - 38
38 - 23.3
23.3 - 5
5 -1.6
1.6 million -10, 000 years
10, 000 years - to present

36.3.01 Elements in the Earth's crust, abundance of elements
Elements can combine to form natural compounds called minerals.
For example, oxygen and silicon combine to form silica SiO2 that occurs as the common mineral quartz.
Table 36.3.01 Elements in the Earth's crust
Element % Mass Element % Mass
Oxygen 46.71 Carbon 0.094
Silicon 27.69 Manganese 0.09
Aluminium 8.07
Barium 0.05
Iron 35.05
Sulfur 0.052
Calcium 3.65
Chlorine 0.045
Sodium 2.75 Nitrogen 0.03
Potassium 2.58
Chromium 0.035
Magnesium 2.08
Fluorine 0.029
Titanium 0.62 Zirconium 0.025
Hydrogen gas
0.14 Nickel 0.019
Phosphorus 0.13 all other elements 0.061

Many different versions exist of tables to show the most abundant elements in the Earth's crust, for example:
Let "most abundant" refer to % of total mass and not the number individual atoms.
On the earth's crust the most abundant element is oxygen, (about 46 %), because oxygen is a very common rock-forming element, together with silicon (28 %).
Other common elements are aluminium (8.2%), iron (5.6%), calcium (4.2%), sodium (2.5%), magnesium (2.4%), potassium, (2.0%).
So aluminium is the most common metal in the earth's crust, which makes up only a tiny portion of the entire earth.
Beneath the earth's crust, the mantle contains 44.8% oxygen, 23% magnesium and 22% silicon, and the mantle makes up about 84% of the earth's volume.
However, the closer to the earth's core the more dense the Earth.
In the core, gravity is so strong the electromagnetic force between atoms is overcome, allowing for fusion fission to occur and the most "stable" form for nuclei
is in the form of iron.
The binding energy per nucleon in the nucleus is the highest in iron-56.
Any element to the left of iron will go through fusion to create iron and every element to the right will go through fission and eventually become iron.
So the most abundant element in the Earth is iron at 32.1%, then oxygen at 30.1%, then silicon at 15.1%, and magnesium at 13.9%.

36.3.02 Elements in the Sun, abundance of elements
Table 36.3.02 Elements in the Sun
Element % Mass
Hydrogen, H
Helium, He
Oxygen, O2
Carbon, C
Silicon, Si