School Science Lessons
9. Energy, kinetic energy and potential energy, work, conservation, conversion, renewable energy
2011-12-25
Please send comments to: J.Elfick@uq.edu.au
Table of contents
9.0 Energy
9.0.0 Energy
9.2.0 Conservation of energy
9.1.0 Kinetic motion
9.3.0 Work, energy
9.2.0 Conservation of energy
9.2.0 Conservation of energy, work, energy, kinetic energy and potential energy
9.2.15 Bow and arrow ballistic pendulum
9.2.1 Children's swing
9.2.2 Drop a golf ball inside a car tyre
9.2.5 Hammer lead and iron, transform kinetic energy to internal heat energy
9.2.18 Height of a ball, high bounce paradox
9.2.7 Hot wire current meter
9.2.14 Loop the loop, energy well track, ball in curved tracks, triple track energy conservation
9.2.12 Nose basher
9.2.19 Prony brake
9.2.1.1 Rebounding ball
9.2.3 Roll-back jar, come back can, boomerang tin
9.2.4 Rotating washer
9.2.10 Solar water heater
9.2.11 Toy spring jumper
9.2.6 Transform electromagnetic energy to kinetic energy
9.2.8 Transmission of compressive energy, motion of first coin and last coin, motion of dominoes
9.2.16 Vertical ballistic pendulum
9.2.9 Wave propagates energy
9.2.13 Weight of a pendulum, break a pendulum wire, stopped pendulum
9.1.0 Kinetic motion
9.1.0 Energy, potential energy, kinetic energy
9.1.3 Aluminium powder twinkles
3.55 Brownian movement
3.58 Clay soil suspension
3.55.1 Diffusion of heavier than air gas, carbon dioxide
10.1.2 Diffusion of ammonia and hydrogen chloride gases
3.55.3 Diffusion of liquids
9.1.2 Heat lump of wax containing lead shot
9.1.4 Hot and cold water drops
9.1.7 Molecular dimensions, size of a molecule
3.56 Particles of matter and dilution
9.1.1 Rattle tin of stones
3.57 Size of a molecule
9.3.0 Work, energy, kinetic energy and potential energy
3.13.0 Energy conversion kJ, mJ, kWh, therm, Btu, calorie, horsepower
36.109 Gravitational potential energy
9.0.1 Renewable energy
5.9 Steam wheel (Primary)
21.0.0 Units of work and energy, joule and calorie, kilowatt-hour
5.8 Water wheel (Primary)
4.199 Water wheels
2.56 Particulate matter and dilution
Put one crystal of potassium permanganate in a test-tube. Add 1 mL water. Dissolve the crystal completely by shaking vigorously, keeping your thumb over the end of the test-tube. Then add water to a total volume of 10 mL. This is a "10 times dilution". Pour this 10 mL of purple solution into a 100 mL beaker and then fill the beaker with water. This is now "100 times" dilution. Fill the 10 mL test-tube with this solution and throw the rest away. Dilute this again in the beaker to 100 mL. It is now a"1, 000 times" dilution. Note how often the solution can be diluted by a factor of 10 before the colour is so pale that it is only just visible. The final dilution factor shows that if matter is particulate, the size of the particles must be small.
2.58 Clay soil suspension
See 3.5.7: micron, µ, micrometre, µm, millimicron, nanometre
Shake a little clay soil with water in a test-tube. Leave this to settle. Note the humus layer at the tiny particles of rock and mineral at the bottom. Filter the liquid. Students will observe that the filtrate is still cloudy, this is because the clay particles have passed through the filter paper. Do students understand why the suspension particles do not settle, even after a few days? The size of colloidal particles is roughly between 1 µ and 100 µ. Divide the filtrate into parts in test-tubes. Keep one as a control. To the other add a few drops of barium chloride solution, or some aluminium salt solution. Note what happens in half an hour and in one hour. The same effect occurs when a clay suspension in a river meets the salts contained in sea water. In many hot countries salt is crystallized from pans built on the clay beds near the mouths of rivers.
9.0.1 Renewable energy
The sources of renewable energy include:
1. Hydroelectric energy
Falling water is used to drive turbines to generate electricity.
2. Solar energy
Solar energy converts energy from sunlight to electricity, an average of 1366 watts per square metre per hour.
3. Biomass energy
Landfill gas, mainly methane gas, CH4, produced by decomposing organic matter, is captured and burned to produce electricity. This method also prevents methane, and other landfill gases, from becoming a potential greenhouse gas in the atmosphere.
Bagasse gas
Waste plant materials, the residual fibrous waste from raw cane sugar processing can be burned to generate electricity.
4. Wind energy
Wind drives turbines to generate electricity.
9.1.0 Energy, potential energy, kinetic energy
Potential energy, PE or EP, is energy deriving from position.
A stretched spring has elastic potential energy, PE = kx2 / 2
An object raised to a height above the Earth's surface has gravitational potential energy, PE = mgh.
Other sorts of potential energy include electrical, nuclear and chemical potential energy.
Kinetic energy, K E,  is the energy of moving objects,  K E = mv2 / 2.
The experiment to show that Ek = ½ mv2 was first done by Willem Gravesande (1688-1742) who dropped brass balls with different velocities into soft clay.
Conservation of energy. Energy can be converted from one form to another, but the total quantity stays the same.
9.1.1 Rattle tin of stones
To imitate the heat movement of gas particles and know the energy of it, put some small stones in a tin with a lid. Replace the lid and shake the tin. You can feel and hear the stones rattling inside the tin. The stones are knocking against the walls of the tin. If you shake much harder, the stones can knock the lid off the tin and burst out. The movement of gas particles in a closed container is similar to the movement of the stones. If you heat the gas particles they move faster and can burst the closed container. Heating a liquid or a gas in a closed container is very dangerous.
9.1.2 Heat lump of wax containing lead shot
To imitate differences of movements of solid, liquid and gas particles, push very small lead shot into wax or petroleum jelly. The lead shot is like the particles of a solid that cannot move about. Put the mixture into a container and melt the wax at the bottom of the container. Heat the container. The wax melts and the lead shot can move around each other limited. The lead shot is like the particles of a liquid. If you burn away the wax and shake the container that lead shot can move in straight lines at random. The lead shot is now like the particles of a gas.
9.1.3 Aluminium powder twinkles
To observe the relation between the twinkle of aluminium powder and its size, add aluminium powder to a beaker of tap water with a few drops of detergent. Stir the mixture. Make the room dark and shine a strong light through the liquid. Observe that the smallest suspended particles twinkle like stars but the larger particles do not twinkle. The reason is that the water molecules hit the smallest aluminium particles and turn them over so that they reflect flashes of light and cause the twinkling. Water molecules cannot turn over the larger particles so they do not twinkle.
9.1.4 Hot and cold water drops
Use a pin to make identical holes in the bottoms of identical paper cups. Mount the cups over drinking glasses. Fill one paper cup with hot water and the other with cold water. Observe the drops of water dripping from the paper cups. The hot water leaks faster than the cold water because the particles have more kinetic energy and so it is easier to overcome the forces of adhesion around the holes in the bottoms of the paper cups.
9.1.7 Molecular dimensions, size of a molecule
Use oil molecules because oil has a density less than water. The oil will float on the surface and not dissolve in the water. If the water has a large enough surface area, you assume that thin oil will spread out in a layer one molecule thick called a monomolecular layer and not form little "hills" of molecules. If you know the volume of oil and the surface area that it forms, you can calculate the thickness of a monomolecular layer by dividing the volume by the area. Use a water container > 30 cm2 so as not to restrict the oil film. Sprinkle the surface of the water with a very fine light powder such as talc powder. When the oil is put on the water, it will push the powder away and the area covered by the oil will be seen clearly. To find the volume of oil, pour thin oil into a burette. Use a thin petroleum distillate. Find the volume of fifty drops by running oil from the burette drop by drop and counting the drops. Allow one more drop to fall on a piece of plastic. Touch the oil drop with the point of a glass rod and then touch the prepared water surface. The oil spreads out. Make an approximate measurement of the area over which it spreads. Estimate what fraction of oil was removed by the glass point by using the glass point to remove successive fractions from the drop until it has been used up. Calculate the volume of oil put on the water and estimate made of the thickness of the oil layer, about 10-6 mm, This is an approximate dimension of a single molecule of the oil.
9.2.0 Conservation of energy, work, energy, kinetic energy and potential energy
See diagram 9.2.0: Direction of displacement at angle θ to the direction of the force
Order online: Mouse Trap Car, energy conversion
Conservation of energy
Energy conversion, convert potential energy to kinetic energy, potential energy and gravity, transfer energy, conservation of mechanical energy in a closed system, problems involving the conversion of mechanical energy GPE <--> KE, EPE <--> KE, gravitational potential energy in its general, non-uniform form, GPE = mgh, GPE = (- G m1 m2 / d) and its application to escape velocity
When an object is moved by a force, F, through a distance in the direction of the force, s, the work done is F X s. The unit of work is the joule, newton metre.
Work = Fs
However if the direction of displacement of the object is at angle θ to the direction of the force
Work = Fscos θ
When work is done on an object the energy of the object changes as stored energy, potential energy and / or as change in speed, kinetic energy. Unit energy is expended when unit work is done. The unit of energy is the joule, newton.metre.
Work done = change in energy so energy is the capacity for doing work.
Kinetic energy, K.E., energy due to velocity = 1/2 mv2. So kinetic energy can be measured by the work an object could do in coming to rest.
If an object moving with velocity u has its velocity increased to velocity v by application of an uniform force F, then the work done is equal to the change in energy
Work = 1/2 mv2 -1/2 mu2
Potential energy, P.E. = change in position or change in state, energy due to position or strain
If an object weight mg newton is raised through a vertical height, h, there is an increase in gravitational potential energy
Potential energy, P.E. = mgh
Change in potential energy may result in a change of state. Steam at 100oC has greater potential energy that water at 100oC. A spring under tension in a jack-in-a-box has the more potential energy than a slack spring. A large molecule, e.g. glucose, has more potential energy than the component molecules. Coal is an example of a store of chemical potential energy.
The sum of kineic energy and potential energy of a body falling freely under gravity is a constant throughout its path.
The "breaking distance" of a moving vehicle involves the work that must be done to bring the vehicles to rest, W = Fs, how much force must be applied to stop the vehicle in a certain distance.
9.2.1 Children's swing
1. Ride on a child's swing. Note the original height of the swing above the ground. Let yourself swing to the other side. The height reached on the other side is almost the original height.
2. Swing a pendulum. Note the original height of the bob. Let the bob make a full swing. The height it reaches is almost the original height.
3. To study the transfer and conservation of mechanical energy, observe a child on a swing. The heights raised at the two sides are always the same. It shows that the potential energies of the swing at the two peaks are equal. If you sit on the swing, you may experience the short rest feeling while reaching the peak then the velocity will become faster and faster. Nip a corner of a handkerchief then observe the angle of the waving when the handkerchief falls from the top point to the bottom point. It may show the velocity reaches the maximum. At the top point the swing and person only possess potential energy but no kinetic energy, at the bottom point their kinetic energy reach the maximum but the potential energy becomes the minimum. When the swing reaches the other peak, the kinetic energy completely changes into the potential energy again. Then at the transfer between potential energy and kinetic energy, is energy lost?
9.2.1.1 Rebounding ball
To observe the transfer and loss of mechanical energy, hold a ball with a strong elasticity, for example, a ping-pong ball, and record its height. Naturally loosen your hand and let the ball falls freely from rest. Observe the heights the ball rebounds several times after the ball falls on the floor and find the relationship among the heights. Repeat a few times to see whether the rebounding height is on earth more than the original some time or not. Redo the experiment on a sandlot instead of the cement floor. Observe the change in shape of the sand as well as the rebounding heights. Compare the phenomena and conclusions on the cement floor and the sandlot. Let students complete the experiment independently then think and discuss following questions: at the process from the ball falling originally to rebounding firstly reaching the peak, how does the mechanical energy change? Why must the rebounding height be equal to or less than the original? At the experiment on the sandlot, how does the energy change? Is the energy in conservation yet?
9.2.2 Drop a golf ball inside a car tyre
See diagram 9.2.2: Ball inside car tyre
1. Hold the ball inside the tyre and note the original height above the ground. Let the ball go. It runs down inside the tyre and up the other side. The height it reaches in the other side is almost the original height but never more. Repeat the experiment using different original heights.
2. Let an outer tyre stand upright on the ground and fix it well. Hold a golf ball with your hand above the tyre and loosen your hand at a certain height and let the ball roll in the groove inside tyre. The ball rolls from the original height to the bottom of the tyre then rolls upwards reaching the original height but not more than the original height absolutely. Repeat the experiment loosening the ball at different heights. The small ball will keep its energy changeless at the whole process of moving if neglect the energy loss due to friction and other reasons. When the small rolls down from the top point to the bottom of the tyre, its gravitational potential energy changes into the kinetic energy, when it rolls up from the bottom point to the top, its kinetic energy changes into the gravitational potential energy again so it comes back the original height.
9.2.3 Roll-back jar, come back can, elastic potential energy and kinetic energy
See diagram 9.2.3: Roll-back jar
1. Use a 10 cm plastic jam jar with screw-on plastic lid. Drill two small holes, each 2 cm from the centre, along the diameter of the bottom of the jar. The distance between the two holes is 4 cm. Drill the same two holes in the cap of the jar. Push an elastic band through each of the two holes in the bottom of the jar. Tie the two rubber bands together outside the bottom of the jar. Pull the ends of the two elastic bands into the jar to cross over then push the two ends through the two holes in the cap. Attach a 50 g weight to one end of a thin wire. Tie the other end of the wire to the rubber bands together where they cross over. Pull on the rubber bands that passed through the cap and tie them so that the weight does not touch the sides of the jar when the jar is horizontal on its side. Hold the jar horizontally and turn it over many times so that the thin wire becomes shorter and shorter. When you hold the jar horizontally and turn it you store potential energy as the thin wire became shorter and the weight became higher. Also, the elastic potential energy is stored in the elastic bands when they are twisted. So the rotating kinetic energy of the jar changes into gravitational potential energy and elastic potential energy. Put the jar on a flat surface. Push the jar ahead and it rolls back. Put the jar on a slight slope. The jar rolls up the slope.
2. Cut two slits, 1 cm X 0.5 cm, in the middle of the bottom and the middle of the lid of a round biscuit tin. Cut a strip of bicycle inner tube rubber length 1 cm longer than the depth of the tin and 1 cm wide. Pass the strip of rubber through the slits and fasten each end outside the biscuit tin with pins through the ends. Attach a heavy machinery nut from the middle of the rubber strip with a wire paper clip. Roll the tin several rotations forward, then let it go and it will roll back. When you roll the biscuit tin forward the heavy nut remains hanging down due to the force of gravity so the elastic becomes twisted tighter with each rotation. The biscuit tin rolls back to release the force of tension accumulated in the rubber strip.
9.2.4 Rotating washer
See diagram 9.2.4: Rotating washer
1. Use a dowel (round stick) 1 m long and a rubber or plastic washers 2.5 cm diameter. The inner diameter of the washer is just larger than the diameter of the round stick. Hold the dowel vertically and attach the bottom end to a table. Hold the washer just above the top of the dowel. Let the washer fall down the length of the dowel. Estimate how long it takes to fall.
2. Hold the washer just above the top of the dowel. Use your thumb and first finger to make the washer spin then fall down the length of the dowel. Note that the rate of fall slows and the speed of rotation increases. The spinning washer at the top of the dowel has rotational kinetic energy and gravitational potential energy due to its height. As the spinning washer falls some of the gravitational potential energy is converted to rotational potential energy so it spins faster. However some of its gravitational energy is lost to friction with the dowel, so it falls more slowly.
9.2.5 Hammer lead and iron, transform kinetic energy to internal heat energy
See diagram 9.2.5: Hammer lead
1. Use a small piece of lead sheet wrapped around one end of a piece of thin iron wire. Hold the other end of the wire. Hit the lead several times. You can feel the temperature rise.
2. Use a thin sheet iron, with thickness not more than 0. 3 mm. Cut a 3 cm width strip off the sheet iron. Wrap the strip around an end of a stick. Make sure the length of the sheet iron, i.e. the length of the strip should be enough to wrap up the stick more than one circle. Hold the other end of the stick with your hand and place the end of the stick with the sheet iron on a wasted block with a slightly smooth surface or an old wooden stool. Touch the sheet iron with your other hand to experience its temperature and remember the feeling. Quickly beat the sheet iron with a mallet until the sheet iron is hot. Take your hand off the sheet iron as soon as your finger feels hot. The thinner the sheet iron is and more quickly beat the sheet iron, more obviously the phenomenon the temperature of the sheet iron rises is. If beat slowly or use some metallic stand instead of the block, the temperature of the sheet iron will not increase so quickly.
9.2.6 Transform electromagnetic energy to kinetic energy
See diagram 9.2.6.1 | See diagram 9.2.6.2 | See diagram 9.2.6.3 | See diagram 9.2.6.4 | See diagram 9.2.6.5
9.2.6.1 To observe the transformation of electromagnetic energy to kinetic energy, place a compass in the tray of a match box. Wind 10 turns of copper wire around the tray so that the wire just covers the compass. Leave two ends of the wire. Rotate the match box so that the compass needle is parallel to the wire. Connect one end of the wire to one terminal of a 1.5 V dry cell or low voltage d.c. power supply. Briefly touch the other end to the other terminal of the dry cell or power supply. Touch the other terminal again after a few seconds. Note how the compass needle behaves at the moment of touching. The compass needle deflects to align itself with the magnetic field produced by the current in the coil.
9.2.6.2 Place a strong horseshoe magnet on its side. Suspend stiff copper wire between the two poles of the magnet like a trapeze. Connect one of the flexible copper wires to a dry cell or d.c. power supply then touch the other copper wire to the cell. The copper wire trapeze will swing away from or towards the magnet, depending on the connection. The motion is due the interaction between the magnetic field and the electric current in the trapeze.
9.2.6.3 Construct a wooden frame as shown in diagram then mount two copper rails 75 mm apart across the centre of the frame. Cut a piece of copper wire 100 mm long to lie across the conducting rails. Mount a horseshoe magnet between the conducting rails so that the rails are a height midway between the poles of the magnet. Connect the conducting rails to a d.c. power supply. Energize the circuit and observe what happens to the copper wire conductor that lies across the conducting rails. It will roll along the conducting rails, the direction depending on the electrical connections.
9.2.6.4 Use a cardboard paper tube that allows a bar magnet to be inserted and removed easily, e.g. centre of a toilet roll. Wind wire around the tube many times to form a coil. Leave about 50 cm at each end of the coil. Connect the coil to a galvanometer or a compass coil as above. Insert a bar magnet quickly into the coil and observe movement of the needle of the compass. Remove the bar magnet from inside the coil and observe the needle again. Rotate the compass to ensure the wire is parallel to the needle pointed to the N-S pole before experiment. If you use a galvanometer, put it far from the coil to avoid magnetic induction. In each case the needle of the compass or the needle of the galvanometer will deflect due to a current being produced by moving the bar magnet in and out of the coil. The deflection of the galvanometer needle is a measurement of the current. The deflection of the compass needle is simply the needle aligning itself with the magnetic field produced by the current in the coil around the compass.
9.2.6.5 Wind insulated wire around an iron core. Connect the coil to a galvanometer. Move a bar magnet back and forth above the coil and observe movement of the needle of the galvanometer. Reverse the magnetic poles and repeat the experiment. Observe the movement of the needle again. Remove the iron core, repeat the steps above and observe what happens.
9.2.7 Hot wire current meter
See diagram 9.2.7: Current meter
The electric current to be measured passes through a platinum alloy hot wire, AC. The current heats the wire so it expands and loosens an attached phosphor bronze wire, BD, that is insulated from heat. One end of a silk strip is attached to the phosphor bronze wire. The silk thread winds around a pulley, E, attached to a pointer then the other end is attached to a spring metal strip that keeps the silk thread tight. When the silk strip becomes loose the spring metal strip moves out to the left, tightens the silk strip that then turns the pulley so the pointer turns to the right. Electrical energy transforms into heat energy into the kinetic energy of the pointer and potential energy of the spring metal strip.
9.2.8 Transmission of compressive energy, motion of first coin and last coin, motion of dominoes
See diagram 9.2.8: Coin motion, domino motion
Longitudinal waves produce compress and stretch in the medium. With the propagation of the form of movement, the energy of the wave propagates. The form of movement is the same to the velocity of energy of propagation under the condition of no chromatic dispersion. It can reach thousands of metres in a second, far surpassing the value of general moving body.
1. Arrange several same coins in a line on the table. You can fix them with adhesive tape. Place one coins in front of the line and place another coin at the end of the line. The last coin touches the one in front of it but is not connected. Shoot the first coin quickly to make it strike the second. Then observe the movement of all the coins. When the first coin hits one end of the line of coins the last coin moves back very rapidly. The energy produced by the first coin transmits rapidly along the line of coins.
2. Use a set of dominoes, or some similar small squares of wood, e.g. mah-jong pieces, on their edges in a long row. Place them face to face. The distance between two dominoes should be shorter than height of them. Push the first one A rapidly. Observe the movement of all the dominoes. As shock dominoes A, it is propagated a small pulse of energy to cause it topples. It knocks against the following domino which knocks the third and so on until finally the end domino falls. It can be seen if you observe that although every domino falls just at its original place and the distance of its motion is very small, the propagation of this pules energy is so quickly that B has begun to fall down before A falls down completely. During propagation of compressive energy, the behaviour of solid particles is like that of the dominoes. Solids consist of atoms, ions and molecules arranged in a row closely together. When one end of a solid obtains the compressive energy due to impact, the particles there produce compressive deformation and the compressive energy is transformed to neighbour particles, and so on. The process of above happens among particles in turn that reaches the other end in a short time and from the particles here propagates the compressive energy to the outside, finally cause the last coin in experiment A shoots forward. In the process above although every particle's motion is very weak, they are much like that connected with small springs going on forward with energy in a form of waves. It has been shown from the dominoes experiment above and analysis about the motion of particles inside the solid that the speed of propagation surpasses far from that of each object when they are connected. Sometimes you can see the similar phenomenon to the dominoes in daily life.
3. If you have visited a train dispatch yard, you can notice the situation of marshalling. As one carriage is connected with the whole train, it collides the last carriage of the train. With a series of reactions that every carriage moves slightly in turn, such energy in a form of shock waves propagates throughout the train rapidly that makes you feel as though the whole train begins to move almost instantaneously.
4. When traffic jam happens in a highway the cars run in a row. At this time if the last car cannot stop in time to collide the back of the car in front of it, the shock wave energy may be propagated forward rapidly that lead to a series of accidents. It is too late to brake the car for all car drivers.
9.2.9 Wave propagates energy
See diagram 9.2.9: Waves
Waves propagate not only the vibration state of the source but also the energy of it. Prepare a water vessel, pour water into it and put a cork by the vessel. Hold a long, narrow wooden rod and make it move up and down in another end of the vessel. Observe the motion of water wave and notice the motion of cork. Increase or decrease the motion and observe what happens about water wave and cork. Increase or decrease the frequency of the motion and observe the situation again. The vibration of a wooden rod caused by hand makes it become a vibration source. The state of its motion and energy propagate out by means of water. Thus forms the water waves. So you can see the wave crest and trough in water. The energy carried by water wave is propagated to the cork causing it vibrate up and down. The cork is up as crest comes, down when a trough comes. The energy of rod vibration propagates to the cork through the medium role of water waves. So the wave propagates not only the state of a vibration source but also the energy of it. Increasing the extent of a shake by hand is increasing the vibration energy of source and water wave increases with it. All this shows that the more the energy the source has, the more energy it propagates and vice versa. If you increase the frequency of a shake by hand, the wave shape varies with it and the distance between the wave crest or that of crest and trough decreases. The vibration frequency of the cork increases too. Waves are the propagators of energy that carried the energy produced by source to all places it arrives.
9.2.10 Solar water heater
Order online: Solar Kit, multi-project  sustainable energy, solar energy
After Davis, Peter and Fries, Peter Australian Science Teachers Journal 33 (4)
1. You do not need a pump to circulate the water to the plastic bottle storage tank. Water in the blackened collector tube absorbs the sun's energy and gets hotter. This hot water is less dense than the rest of the water so it rises out of the collector into the storage tank. The cold water at the bottom of the bottle then flows into the bottom of the collector and the cycle begins again. This process is called thermo-syphoning. You need water based black plastic paint, -10oC to 110oC thermometer, adhesive tape, roof and gutter type silicon sealer or "Blue Tack", plastic bottle with lid for the water storage tank, dry cleaning wrap or "Glad Wrap" plastic film, plastic funnel, roll of aluminium foil, tie wire. Paint inside the collector black and paint the hose. Attach clear plastic wrap, clear acrylic or glass. Use the blue tack or silicon sealer to attach the collector to the plastic bottle (tank). Place the plastic bottle above the collector.
2. To test the solar heater:
2.1 Put cold water in your solar water heater, e.g. 4 litres.
2.2 Record the temperature of the cold water.
2.3 Put your solar water heater in the sun or use a strong lamp.
2.4 Record water temperatures every 5 minutes for 1 hour.
2.5 Calculate the amount of heat energy gained by the water in your heater in 1 hour.
Heat (Joule) = m x c x DT, where m = mass of water = (volume in cm3 for water), c = (specific heat, 4.2 Joule / g for water), DT = temperature increase, (final temperature - initial temperature). How could you make improvements to increase the efficiency of your solar heater? Calculate the efficiency of the solar collector: Percentage Efficiency = (Energy input / Energy output) X (100 / 1). Energy input from the sun falling on 1 m2 = 800 x number of seconds collector exposed to sun, J per m2. Energy input after 1 hour in the sun = (800 x 60 x 60 J per m2) = (2, 880, 000 J per m2) = (288 MJ per m2). Adjust this figure for the surface area of your collector.
9.2.11 Toy spring jumper
Compress a spring under a toy held down be a suction cup
9.2.12 Nose basher
Hold a bowling ball suspended from the ceiling against your nose and let it swing with pushing it or in any way giving it any additional velocity. It will not bash your nose because it must return to the original height on the back swing
9.2.13 Weight of a pendulum, break a pendulum wire, stopped pendulum
Suspend a pendulum from a double beam balance with a small block placed under the opposite pan to keep the system level then swing the pendulum so it just lifts a weight off the stopped pan. Suspend a heavy bob on a weak wire, as the ball descends in its swing the wire breaks. A pendulum is started at the height of a reference line and returns to that height even when a stop is inserted stopped pendulum
9.2.14 Loop the loop, energy well track, ball in curved tracks, triple track energy conservation
A ball rolls down an incline and then around a vertical circle. Vary the initial height of the ball. A water stream loop the loop shows the effect of centripetal forces much more dramatically then when a ball is used water. The reverse loop-the-loop is placed on a cart hooked to a falling mass that produces an acceleration just large enough to make the ball go around backwards into the cup. A ball can escape the energy well when released from a point above the peak of the opposite side. Balls are rolled down a series of curved tracks of the same height but different radii. Balls released from three tracks with identical initial angles rise to the same height independent of the angle of the second side.
9.2.15 Bow and arrow ballistic pendulum
The relation between bending of the bow and the velocity of the arrow was found to be linear. Coffee can target for a bow and arrow ballistic
9.2.16 Vertical ballistic pendulum
A ball is dropped into a box of sand suspended from a spring and the extension of the spring is measured.
9.2.17 Big yo-yo
A large yo-yo is hung from bifilar threads wrapped around a small axle. The string unwinds on the way down and rewinds on the way up. Low cost yo-yo made with cardboard sides and paper towel centres.
9.2.18 Height of a ball, high bounce paradox
A device to project a ball upward at different known velocities to show dependence of kinetic energy on the square of velocity height of a ball. A steel ball is launched upward by a stopped spring which the initial velocity is calculated. Flip a half handball inside out and drop on the floor and it bounces back higher than the height from which it was dropped.
9.2.19 Prony brake
Each end of the belt for a Prony brake is attached to a spring scale. Measuring your horsepower by Prony brake Measuring delivered horsepower by turning a pulley under a stationary belt attached to spring scales at each end. Rotate a shaft against a constant frictional resistive force.