School Science Lessons
Primary Science Lessons
Year 6
2009-10-23
Please send comments to: J.Elfick@uq.edu.au
Suggested answers to the teacher's questions are shown within [square
brackets].
Table of contents
6.18 Measure air pressure
6.19 The moon and tides
6.20 Southern Cross constellation
6.21 Estimating
6.21.2 Estimate total number using areas
6.21.3 Estimate total number using divided samples
6.21.4 Estimate total number using layers
6.21.5 Estimate lengths using your body
6.21.6 Estimate heights
6.21.7 Estimate area of a leaf
6.21.8 Estimate area of a mouse
6.21.9 Estimate weight
6.22 Pendulum tells the time
6.23 Trees and shrubs
6.24 Trees, palms and ferns
6.25 Protect our trees
6.26 Describe grasses
6.27 Describe palms
6.28 Describe ferns and mosses
6.29 Protect our coral reefs
6.30 Protect our
soils
6.31 Describe soils
6.32 Test soil texture
6.33 Fertilizing soil
6.34a Chemical fertilizers
6.35 Burn candle over water, candle burning in
inverted jar over water
6.36 Candle "lava"
6.36.1 Cooling candle wax, speed of cooling
and
crystal size
6.37 Electric circuit
6.38 Electricity conductors
6.39 Electric torch (flashlight)
6.40 Hanging magnets
6.41 Make electromagnets
6.18 Measure air pressure
See diagram 4.272: Air pressure
Be able to state how atmospheric pressure (air pressure)
affects weather.
Use Coins, glasses of water with cardboard lids, drinking
straws or tubing.
If you have a simple barometer or aneroid barometer you
can use it in the lesson. The average mean sea level pressures for
example at Honiara in millibars (mb) are as follows:
| June |
9 a.m. |
1 010.7 mb |
3 p.m. |
1008.8 mb |
| December |
9 a.m. |
1 007.9 mb |
3 p.m. |
1006.2 mb |
1. Give each group a coin. Wet one side and then press it on the
forehead. Why does the coin not fall down? [The air presses it against
the forehead.]
2. Give each group a glass full of water covered with a cardboard lid.
Turn it upside down. Why does the water stay in the glass? [The air
presses the cardboard against the water.] In which direction does the
air press? [The air presses in all directions.]
3. Give each group a straw or tube and a glass of water. Suck on the
straw until the water is half way up it. Why does the water go up the
tube? [When you suck in some air, the air pressure in the straw becomes
less. Then the air pressing on the water in the glass pushes some water
up the straw.] Put your first finger over the top of the straw and hold
up the straw. Why does the water stay in the straw? [The air is
pressing up.]
4. Explain that air pressure can change. Air pressure is greatest at
sea level and gets less with height. Air pressure can also change at
one place. When the air pressure is fine, the weather will stay fine.
When the air pressure is low, rain clouds will come and there will be
wet weather. Very low air pressure occurs before a cyclone.
5. Air pressure is measured with a barometer. This is a tube closed at
one end. The other end is open in a bowl of mercury. Mercury is a very
heavy liquid. When the air pressure is high, the mercury is pushed high
up the tube. When the air pressure is low, the mercury is lower in the
tube. On a fine day at sea level the atmospheric pressure is 760 mm of
mercury.
Extra Activity: Read a barometer every day. Note when is the pressure
high and when is the pressure low. Make a table to show some daily
records of air pressure at 9.00 a.m.
6.19 The moon and tides
Be able to observe the moon and tides and try to find a
connection between their movements.
Use Custom stories and observed movements of the moon.
This activity consists of three parts: custom stories
about the moon and tides, movements of tides, movements of the moon.
There are many interesting stories about the moon. Some people see a
woman weaving baskets in it. Some people think it is a friend of
Haley's comet, which reappears every 76 years, called the smoking
star. The palolo worm which is a swimming annelid worm, rises to the
surface on the second night after the full moon in November. Then they
mate and lay their eggs. Try to find out the times for high and low
tide and the phase of the moon.
1. When do you get high tides and low tides during the day? [There are
two high tides and two low tides each day about 12 hours apart.]
2. Are the heights of the high tide and low tide always the same
during the month? [No.]
3. Are the heights of the high tide and low tide the same during the
year? [No.]
4. What else changes during the month? [The moon.] How does it change?
[First there is a new moon when you can hardly see it then it gets
bigger until a full moon, then it gets smaller.] How many days between
full moon? [30.] How many days in a month? [About 30.]
5. Can you see any connection between the moon and the tides?
6. Can you remember any custom stories about the moon and the tides?
Extra Activity: Wall chart on the phases of the moon. Rule the chart
into squares and number the squares with the dates of the month. Each
evening a different child has to look for the moon then draw it on the
chart the next day. Wall chart on the tides, tide during the day.
Measure the depth of the tide each hour and mark on the wall chart.
Measure the highest tide and lowest tide each day and mark on the wall
chart.
The Sun-force is about 5 / 11 of the Moon-force on the earth but they
can act conjointly. When a high tide occurs on one side of the Earth a
high tide occurs on the other side of the Earth. Spring tides are
higher than other tides and occur just after new Moon and full Moon
when the gravitational attraction of both the SUN and the MOON act in a
direct line. Spring tides are nothing to do with the spring season.
They "spring up" higher than the other tides. When the Moon is at first
quarter or third quarter, the tide is minimum, has the least rise and
fall, and is called the neap
tides The rise and fall of the neap tides is about half that of the
spring tides.
6.20 Southern Cross constellation
See diagram 36.19.2: Southern Cross
constellation
Be able to observe the movement of stars in the Southern
Cross constellation.
Use Evening and night observations of the stars in the
Southern Cross and custom stories about it.
Make sure you can find the Southern Cross and pointers.
When you have done that, you can show the position of this
constellation to children who will do their observations at night.
1. Draw the Southern Cross constellation and pointers on the chalk
board and show the children in what part of the sky these stars can be
seen.
2. Look for these stars that evening. The next day, make sure that you
really did see the Southern Cross. Then tell the children to observe it
the next evening at three different times: 6:00 p.m., 7:00 p.m. and
8:00 p.m. Draw it and another object such as a tree at these times.
3. The next day, look at their drawings. Do you realize that the
Southern Cross and all stars appear to move in a circle to the right?
This shows that the earth is turning.
4. Show the children how to find South by extending Gamma, Alpha Crusis
X 31/2, then dropping to the earth.
Extra Activity: Do you know any traditional stories about the Southern
Cross? Some people said that the Southern Cross is a fishing net
suspended on four poles and the pointers are two fishermen. Some people
said that the appearance of the Southern Cross in March told them to
start planting yams.
6.21 Estimating
See diagram 2.6.21: Estimates
6.21.1 Estimate total number using volume
You will need a jar full of seeds, e.g. bean seeds
1. Fill a matchbox with seeds from your jar.
2. Count the number of seeds in the matchbox. Record the number (N1).
3. Find out how many matchboxes of seeds there are in the jar. Record
the number (N2).
4. Multiply the number of seeds in the first matchbox by the number of
samples (N1 x N2).
5. Record this estimate in the table.
6.21.2 Estimate total number using areas
1. Draw 10 squares as in the diagram
2. Pour seeds onto the paper to completely cover one square, one seed
thick.
3. Count the number of seeds in this square (N1).
4. Continue to add seeds to the squares until you have used all the
seeds in the jar. Count how many squares you used. (N2)?
5. Multiply the number of seeds in the first square by the number of
squares used (N1 x N2).
6. Record this estimate in the table.
Compare this estimate with the estimate for 1A. Are the estimates
similar? Which estimate do you think is best? If you have estimates
from different groups in the class calculate the average estimate.
6.21.3 Estimate total number using divided samples
You need 5 glass jars of the same size.
1. The first jar is full of seeds.
2. Pour seeds from the first jar into a second jar. Each jar contains
half the seeds. Each jar contains an equal number of seeds.
3. Pour seeds from the second jar into a third jar. The second and
third jar contain the same amount of seeds. They now contain a quarter
of the original volume of seeds.
4. Repeat this procedure twice. The final set of jars is as in the
diagram. The sample is contained in jar number 5. Count the number of
seeds in jar number 5. It contains 1/16 of the total. Multiply the
number of seeds in jar number 5 by 16.
6. Record this estimate in a table.
7. Count the number of seeds in the first jar by counting out the seeds
in piles of ten. Record your actual number in a table. Which of your
estimates was closest to the actual number of seeds?
6.21.4 Estimate total number using layers
Use a full box of matches but do not count them. Open the box. Count
the number of matches you can see on in the top layer. Count the number
of layers in the box. If you assume the same number of matches in each
layer, you can estimate the number of matches in the matchbox. Use this
method to estimate the number of seeds in the jar. Can you use this
method to estimate: 1. The number of bricks used to build your
classroom 2. The number of sticks of chalk in a box 3. the
number of words on a page of a school textbook?
6.21.5 Estimate lengths using your body
Use a ruler to measure in centimetres these parts of your body: 1. The
top joint of your thumb. 2. The length of your forefinger. 3. The
span of your hand (see diagram). 4. The distance between the thumb
and the nose when your arm is outstretched. This is for measuring cloth
or rope. These parts of your body can all be used for measuring short
lengths, e.g. the length of your desk, or the height of a plant. Which
distance would you use to plant seeds about 15 to 20 cm apart? For
distances on the ground you can use the length of your foot, or the
length of a stride. Measure the length of a normal walking stride. Use
it to estimate the length of a football pitch. Mark out distances of
one metre along a straight line. Walk along this line. Make each stride
one metre long. Remember what it feels like. Use it to estimate the
length of a football pitch. Then measure the football pitch. Which of
your two estimates is best?
6.21.6 Estimate heights
Estimate the height of a flag pole or a tree. You need a stick, or a
ruler, and a stone.
1. You and your friend should stand on lines at right angles to each
other as shown in diagram 1.
2. Hold your ruler in front of you and move either forwards or
backwards until it appears to be the same size as the flagpole (diagram
2). The bottom of the ruler should be in line with the bottom
of the flagpole. The top of the ruler should be in line with the top.
3. Do not move your hands. Let the ruler turn until it is horizontal
(diagram 3). The left end of the ruler is still in line with the base
of the flag pole. Ask your friend to put a stone on the ground where it
is in line with the end of the ruler.
4. Measure the distance between the stone and the flag pole. This is a
good estimate of the height of the pole.
6.21.7 Estimate area of a leaf
The areas of squares and rectangles can be measured so you can use
these to estimate other areas, e.g. the area of a leaf.
6.21.8 Estimate area of a mouse
Rectangles of paper could be used to estimate the body area of animals,
e.g. The body area of a mouse. Use this method for estimating the area
of your skin. You will need lots of newspaper, pins, scissors and a
ruler.
6.21.9 Estimate weight
Lift one kilogram. Feel the weight. Lift different things, e.g. bag of
potatoes, house brick, bucket of water, school bag, your friend. Can
you estimate their weight in kilograms?
Know the feel of these weights:
10 grams = the weight of 4 drink bottle
tops
1 kilogram = the weight of 1 litre of water
10 kilograms = the
weight of 10 litres of water.
Use a balance to estimate the weight of
small objects of the same size, e.g. pins and paper clips.
Useful ways to measure and approximate size
1 teaspoon (the smallest spoon) 4.5 mL
1 dessertspoon (the spoon you eat with) 10 mL
1 teacup (the cup you use with a saucer) 200 mL
1 matchbox volume 25 mL
Area of the top of a matchbox 20 cm2
1 gallon container holds 5 L
1 fluid ounce container holds 30 mL
Human body temperature 37oC (Celsius)
Weights of one matchbox full of fertilizer
Ammonium sulfate (sulfate of ammonia) 26 g
Potassium chloride (muriate of potash) 24 g
Single superphosphate, "super" 22 g
Triple superphosphate, "super" 20 g
Sulfur 20 gm
6.22 Pendulum tells the time
See diagram 15.1.1: Pendulum technical diagram
Be able to observe the effect of changing: the swing,
length, and weight of a pendulum on the time taken for each swing.
Use string, a pendulum bob, stop watch or watch with second
hand. Set up a pendulum so that you can change the length of the string
and weight of the bob.
Set up the pendulum as in the diagram. The distance from the
knot to the centre of the bob should be exactly one metre. The time for
one complete swing is the time between movements over the arrow in the
same direction. Pull the bob a few centimetres to the side then let go.
Then try with a big swing. Then try with a shorter swing. Then try with
a one metre swing and heavier bob.
The time for a swing is the time for the pendulum bob to go forwards,
then backwards to where it started.
Fill in the table, for example:
| Length |
Weight |
Size of swing |
Time for one swing |
| 1.0 m |
1.0 kg |
big swing |
2 seconds |
| 1.0 m |
0.5 kg |
big swing |
2 seconds |
| 1.0 m |
0.5 kg |
small swing |
2 seconds |
| 0.5 m |
0.5 kg |
big swing |
about 14 seconds |
| 0.5 m |
0.5 kg |
small swing |
about 14 seconds |
| 1.5 m |
0.5 kg |
big swing |
about 25 seconds |
| 1.5 m |
0.5 kg |
small swing |
about 25 seconds |
Extra Activity: Watch a swinging pendulum very closely. Where does
it move fastest? [In the middle of the swing when the bob is passing
the arrow.] When does it move slowest? [At the end of each swing when
it stops then changes direction.]
6.23 Trees and shrubs
See diagram 9.53.9: Different trees
Be able to identify and describe some trees, shrubs and
herbs in the locality.
Use local examples of herbs, shrubs and trees, plant
presses.
The plants you know as trees, shrubs and herbs or bushy
plants have the parts of their flowers in fives, leaves shaped like
hands with three parts, a tap root, and the trees and shrubs are woody.
Trees are tall with usually one main stem. Shrubs are smaller and
branch near the ground. Trees include the mango tree, cassia trees,
Acacia, Casuarina or she oak and Ngali Nut tree. Shrubs include
Euphorbia, Hibiscus, side herbs include most weeds, e.g. Commelina.
1. Explain the difference between trees, shrubs and herbs and show the
children some examples. [See the differences above.]
2. Look at a herb. Does it have a stem? [Yes.] What is the shape of
the leaf? [Like a hand.] What kind of root does it have? [A tap root
and smaller roots.] Does it have flowers? [Yes.]
3. List all the trees, shrubs and herbs you know. They may have to
stroll around the area.
4. Some herbs are thin stemmed vines, some are called climbers, e.g.
passion fruit (Granadilla) and Bougainvillaea.
Some are creepers, e.g.
Basella (Indian Spinach.) 5. Garden Walk
See the trees, shrubs and herbs.
Extra Activity: Display of cut out shapes of trees, shrubs and herbs.
Hold a piece of paper up and draw the shape of the tree on it. Cut it
out and stick it on the display board. Can you tell a tree by its
shape? You could also display herbarium specimens of various trees,
shrubs and herbs. Can you identify the specimens?
Extra Activity: Collect different fungi.
6.24 Trees, palms and ferns
Be able to identify some trees, palms and ferns.
You should know some examples of the trees, palms and
ferns listed. Bring a branch of a tree, leaf of a palm and a whole fern
into the classroom, e.g. Acacia (clearings), Albizia (fuelwood tree),
Betel palm, Bracken Fern, Breadfruit, Campanosperma (swamp tree), Lemon
and lime (citrus), Cocoa, Coconut, Coffee, Edible Fern, Takuma,
Epiphytic Ferns (live on trees), Eugenia (forest tree), Fig, Filmy
Fern, Guava, Ivory Nut Palm, Kamarere (Eucalyptus deglupta), Leucaena
(shade tree), Mango, Mangrove (swamp tree), Ngali nut (Canarium), Nipa
palm, Oil Palm, Pandanus palm, Papaya, Podetia (forest tree), Rubber,
Securingia (fuelwood tree), Soursop, Teak, Terminalia (forest tree),
Traveller's palm.
1. Show the children samples of trees, palms and ferns. What is the
main difference? [The shapes of the leaves.]
2. Draw some leaves of each, e.g. cocoa leaf, palm leaf, fern leaf.
3. Which trees, palms and ferns can they name? What are the uses of
these plants?
4. List all the trees, palms and ferns they know.
Extra Activity: Naming Game.
Take the children for a walk. What are the names of the trees, palms or
ferns seen during the walk? Sentence completion: The three main kinds
of large plants are as follows: 1. [Trees, e.g. Breadfruit, Leucaena]
2. [Palms,
e.g. Coconut] 3. [Ferns, e.g. Takuma].
Extra Activity: Collect the following stages of a known tree, e.g.
mango or Terminalia, seed, young plant, plant with flowers and
fruit.
6.25 Protect our trees
See diagram 9.53.9: Conserving trees
Be able to state why you should carefully protect your
bush
trees.
Use Trees are part of out natural heritage. We should make
sure that all the different kinds of trees in your forests will be
there
in the future for the next generations. Forest trees have survived for
thousands of years so why should you worry about them now? The
population is increasing rapidly so there are now more people who want
to use the products of the forest. Trees can be cut down easily by
modern equipment such as chain saws. Logging of a forest has the result
that all the largest trees are cut out. They may grow again. Cutting
down a forest for wood chipping means that all trees are cut down and
the same type of forest may never grow there again. Burning off grass
lands kills any small trees.
1. Explain the importance of the forest. It is not just the bush. It
has been a source of benefit for the people for a long time. Divide the
class into groups. Each group must list the benefits to the people of
the forest. Read out their list. Summarize the benefits on the chalk
board.
2. List the names of bush trees that benefit people, e.g. cotton tree
for stuffing pillows, Kamarere for timber and fuelwood, local nutmeg
for eating.
3. Why you should not burn grassland? [The small tree seedling cannot
grow and so the forest shrinks.]
4. What can you do to tell other people to conserve your trees?
Extra Activity: Talk from a forestry officer. The teacher should have
previously informed the officer ahead of time for this exercise.
6.26 Describe grasses
See diagram 9.52: Grasses
Be able to 1. describe and identify the parts of grass
and how they grow and 2. distinguish between grasses and sedges.
Use Grasses are the most useful group of plants. They have
many small flowers and, except bamboo, grow close to the ground as
runners or tufts. They have a special shape of leaf. Each leaf has a
leaf blade, sheath and a ligule. They have parallel veins. Sedges have
angular stems while grasses have round stems.
1. Give each group different kinds of grass. What do you call these
plants? [Grass.] How are they different? [Tufted grass grows upright in
a clump, rumour grass grows along the ground, bamboo is very tall and
has a woody stem, cereals have large grains that you can eat.]
2. Look at the tufted grass and runner grass. How are the grasses
different from bushes and trees? [Grasses are small plants, they may
cover the ground, they have very small flowers and seeds, cereals
produce grains. They have fibrous roots.]
3. Describe the grass roots. [Lots of small roots that grow from the
same place, bushes and trees have a long tap root and smaller roots
from growing along it.]
4. Describe the grass stem. [Most grasses have no stem, cereals and
bamboo have a kind of stem that may be hollow.]
5. Describe the grass leaves. [The leaves are quite different from the
leaves of bushes and trees, grass leaves are long and thin, part of
them wraps around the other leaves or stem and part hangs down when it
is old.]
6. Can you see the grass flowers? They are very small. Large grass
seeds are called grain.
7. Pull off a while grass leaf and draw it.
(8) Pull off a sedge stem and compare with a grass stem.
Extra Activity: Drawings of grass plants.
6.27 Describe palms
See diagram 9.50.2: Palms
Be able to describe different palms and how they grow.
Use examples or pictures of palm plants, mosses
and ferns. Edible palms include coconut, sago, oil and date palms.
1. Give each group a piece of palm leaf. What kind of plant is it
from? [Palm.] How is it different from the fern or moss leaf? [It is
much bigger, hard and shiny, divided into strips.]
2. How many useful palms do you know? [Coconut, sago, raphia, nipa,
betel, oil palm, pandanus.] Do you know a useful palm that grows in the
desert? [date palm.] There are many other kinds of palms in the forest.
Do you know any use for them?
3. Show the children a picture of a palm tree or show them a palm
outside.
What do you notice about the following parts of a palm?
The stem [It grows straight up, no branches.]
How the leaves grow [The leaves grow from the top of the stem, the
youngest at the tip, the oldest hang down.]
The size of the leaves [The leaves are very big.]
The shape of the leaves [Split into strips or fan-shaped.]
The roots [Shallow roots that may stick out before going into the
ground.]
The fruit [They can be large and heavy.]
4. Palms are one of the most useful plants in the world. Palms are
also special trees in the forest. They grow very slowly so you should
not cut them down unless you have a good reason. Be kind to palms.
Extra Activity: Visit the forest and study the sago palm. Before it
flowers, you cut it down and wash the sago starch out of its trunk. The
leaves make good palm thatch.
6.28 Describe ferns and mosses
See diagram 9.48.0: Ferns | See
diagram 9.47.2: Moss
Be able to collect and describe different ferns and
mosses.
Use Different types of ferns and mosses:
1. tiny, filmy ferns 2. bracken ferns that grew up out of the ground
3. tree ferns that are tall and have a kind of trunk 4. epiphytic
ferns that grow high up on other plants and grow high up
on other plants to reach the light 5. magnifiers.
Ferns do not have flowers, seeds or fruits. They reproduce
by tiny round spores from the underside of their leaves called fronds.
If they press a frond down on to inked paper, you can get an outline of
where the spores are made. Ferns usually live in damp places or in the
forest. Mosses are tiny single plants that crowd together like the pile
of a carpet. Ferns are found in damp places. They have root-like
structures called rhizoids Use ferns to the lesson or
prepare to go out to the forest to see different kinds of ferns.
Collect ferns with brown spores underneath. The spores underneath are
called sori, singular "sorus". They are used for reproduction.
1. Show the class the different kinds of ferns and mosses. Have you
seen them before? Can ferns be poisonous? [Yes, some ferns can make
cattle sick if they eat them.]
2. What do you see on the fern leaf (frond)? [Brown balls are under
the frond.] They are called spores or sori and are like little seeds.
They are used for reproduction.
3. Draw a fern leaf. How is it different from the leaf of a tree? [It
is much thinner and has a different shape.]
4. Does it have flowers and fruits? [No.] Does it have a stem? [Some
have a kind of stem.] Does it have a tap root? [No, it has little
roots.]
5. Look at a piece of moss carpet. Can you see the separate moss
plants standing up straight? Can you separate one moss plant? Why do
they all stand closely together? [To keep water between them and not
get dry.] Look at a single moss plant with the magnifier. Does it have
flowers? [No.] Does it have leaves, stem and root? [Yes, but they are
very small and simple.]
Extra Activity: Make spore outlines on inked paper, or draw a harvested
sample from a moss plant. Use the magnifier for the initial
observation.
6.29 Protect our coral reefs
See diagram 4.62: Conserving land
Be able to explain why you should stop loss of land and
coral reefs by controlling water runoff.
Use Examples of ridges and terraces.
If land is perfectly flat it cannot be washed away by
rain, but it may be cut away by a river. Heavy rain can cause loss of
nutrients by leaching. Sloping land can be washed away if water washes
over it. Loss of land can be prevented by covering the soil with grass
and trees. When people make gardens on slopes some soil will be washed
into the valley below to become valuable topsoil. However, that topsoil
will be lost if it is washed into the river and becomes silt. The silt
can cover the animals in the coral reef and kill them. Children should
know how to prevent loss of land and coral reefs.
1. What will happen to the bare soil on slopes if it rains? [It is
washed down.] Where does it go? [On to the land below.] Where can it
go? [Into the river.] Where does the silt go? [Out to sea, it can cover
the coral.]
2. How can you stop water washing the soil down? [1. Grow crops in
horizontal strips 2. Build terraces to hold the soil back 3. Dig
horizontal ridges 4. Dig drains to carry water away.]
3. What is the best way to protect a sloping level? [Cover with
plants.]
Extra Activity: Visit to ridges and terraces.
6.30 Protect our
soils
See diagram 4.62: Strip cropping
Be able to explain why you must change the traditional
methods of gardening and burn less bush.
Use Traditional gardening environment, modern improvement
methods showed and explained by agricultural officers.
This lesson is not designed to teach children that the
traditional methods of gardening were wrong. They were excellent
methods because they allowed soil fertility to be restored by the
forest and efficiently used the garden land by having a variety of
sized food plants growing in the gardens. They provided enough food for
the people. The system should be changed now because of the growth of
population. However, you should try to improve the traditional methods.
1. Describe their traditional method of shifting cultivation.
2. Explain that the hot wet climate of the Solomon Islands helps all
plants to grow very quickly. The result is that in traditional
gardening you cannot use the garden for more than a few years because
the fast growing weeds take over.
3. Another reason that people shift a garden is that the crops take
out nutrients from the soil, especially potash and phosphorus and so
the soils become less fertile. 4. The traditional method was to let
the forest grow back over the
garden land and not use it again for 15 to 20 years. This is called the
bush fallow system. During this time the rotting leaves from the forest
would restore the soil fertility.
5. However, now the population is increasing rapidly and the people
are
moving to towns. There is not enough land to allow the long fallow
periods so people are using the land again for gardens before soil
fertility is restored. Forest is changing to grassland and soil is
being washed away.
6. Agricultural officers believe that one way to conserve soil
fertility would be less burning of cleared land. Burning of loose
leaves and sticks returns some nutrient to the soil in the ash and it
also kills some diseases and weed seeds. However, some plant nutrients
are lost in the smoke. Much ash is washed away, the bare ground is
eroded by heavy rain and plant nutrients can be washed away or leached.
7. The best method is to cut the trees low but not harm the stumps so
that they can grow again easily. This is called secondary forest
regeneration. Burn the wood and trash that get in the way but use the
leaves for mulch.
Extra Activity: Visit a traditional garden to see how the cut bush is
burned.
6.31 Describe soils
See diagram 4.36.3: Examining soils
Be able to link different types of soils with their
physical properties.
Use A large container of garden soil, different kinds of
soils, e.g. sand, clay, swamp, magnifiers, sheets of paper (the
different soils should be placed on these), glass jars, buckets of
water, table of results.
Examine soil
types with special reference to the texture types.
1. Give soil samples and other materials to each group. Label each
soil sample Put garden soil in the glass jar, until it is about one
third full of soil. Pour water from the bucket into the jar containing
the soil until the jar is two thirds full. Put the lid on the jar and
shake strongly, watch what happens inside the jar for a few minutes.
[Solid particles settle to the bottom.]
2. What do you see from top to bottom in the jar? [Floating plant
matter, clay suspended in the water, fine sand, coarse sand, pebbles.]
Put this jar where it will not be moved as they will be looking at it
later in the lesson.
3. Take each sample of soil (including garden soil) and feel and look
at each closely with the magnifier to see: the colour, the way the soil
holds together, the size of the particles, how much water there is in
the soil, how much plant matter there is in the soil, if any animals
are present, the feel of the soil.
4. Complete their table of results.
Extra Activity: Use another soil sample from home for
further testing.
Table of Results
Which soil has the darkest colour? [Swampy soil.] Which soil feels the
most sticky? [Swampy soil.] Which soil feels the driest? [Sandy soil.]
Which soil is held together most loosely? [Sandy soil.] Which soil has
the most plant matter? [Garden soil or swamp soil.]
6.32 Test soil texture
Be able to show a simple method of determining the texture
of soil.
Use Samples of different soils, e.g. clay, silt, sand and a
small quantity of water.
The texture of a soil affects soil characteristics such as
ease of cultivation, its ability to accept water and how much water it
can hold for plants and other organisms to use. A quick and simple
technique to measure soil texture is useful when deciding agricultural
activities such as ploughing.
Soil Texture Reference Information
Sands, grains do not stick together, cannot be moulded, single grains
stick to fingers.
Loamy sands, form fragile shapes that just bear handling, give short
ribbons that break easily, discolour fingers.
Fine sandy loams form shapes that will just stand handling, fine sand
can be felt in some, otherwise it feels smooth, may feel greasy if much
organic matter is present, will form ribbons 15 to 25 mm long.
Silty loams, will stick together but will crumble, very smooth and
silky, will form ribbons 25 mm long.
Clay loams, sticks together to form shapes, with a rather spongy feel,
plastic when squeezed between thumb and forefinger, smooth to
manipulate, will form ribbons 40-80 mm long.
Clays, smooth, plastics casts, some resistance to manipulation
(toughness), form ribbons at least 80 mm long, depending on heaviness
of the clay.
Sand grains can be felt in sandy clays that form ribbons 40-50 mm long.
1. Take a small amount of soil enough to fit in the palm of the
hand. Discard obvious pieces of gravel.
2. Moisten the soil with water, a little at a time and knead until
there is no apparent change in the feel of the ball. The moisture
constant should be such that the ball just fails to stick to the
fingers.
3. Inspect the sample to see if sand is visible, if not, it may still
be felt and kneaded as the sample is worked.
5. Finally, squeeze it out between the thumb and forefinger with a
sliding motion and note the length of self-supporting ribbon that can
be formed.
6. Give the children some pure sand, silt and clay to test. Then test
soil from 1. a garden 2. a forest 3. bank of a river 4. top of a
slope.
Extra Activity: Texture museum. Try to collect samples of soil with the
six types of texture. Keep them in glass jars for reference.
6.33 Fertilizing soil
See diagram 6.65.1: | See
diagram 6.65.2: | See diagram 6.65.3:
Nitrogen cycle | See
6.9.14: Composting
Be able to state the four reasons for fertilizing soil.
Use A drawing of the soil nutrient cycle, evidences of
fertilizer activities and soils in the surroundings.
To fertilize means to make the soil richer by adding plant
nutrients that will make the crops grow better and produce a greater
yield when they are harvested. There are four reasons why the soil must
be fertilized: 1. Some soils have been formed from rocks that did not
have enough of the chemicals that make plant nutrients. In some
tropical countries the parent rock has little potash in it and so the
soil formed from that rock will be deficient in potassium. 2. Soils
may lose plant nutrients when rainwater washes through them. This is
called leaching. Soils that have an open texture and do not have enough
clay and rotten plant material in them lose many plant nutrients by
leaching. 3. When a crop is harvested and taken away, some plant
nutrients are taken away as well. These plant nutrients must be
replaced if the soil is to remain fertile and produce good crops. Some
plants need more of some particular plant nutrients than others. You
take away many those nutrients when the plants are harvested. 4.
Fertilizing increases the yield of a crop and allows us to feed more
people or make more profit if the crop is sold. The work done in making
compost and adding it to the soil is rewarded by an increase in profit.
The plants get only a small fraction of their total plant nutrients
from the soil. Most of the nutrients come from the air. However, crops
will not grow well unless they have all the plant nutrients they need.
[In this lesson you can teach the four reasons by using the diagram
shown in the diagram. Draw the diagram on the chalk board. Start with
the soil, then the sweet potato, then the pig, then show the loss of
nutrients to the market and by leaching.
1. Today you will learn the four reasons why you must fertilize the
soil. We will learn from a diagram. First, here is the soil. The soil
contains plant nutrients such as nitrogen, phosphorus and potash. We
can see rocks deep in the soil. Are all the rocks the same? [No.] Do
all rocks give the same nutrients? [No.] In some places the rocks are
usually old coral reefs or volcanic rocks. These rocks do not contain
much potash, so the soil needs more potash.
2. What happens to the soil nutrients? [They go into the sweet potato
plant.] What else goes into the plant, it is shown in circles.
[Sunlight, carbon dioxide, water.]
3. How do the nutrients get out of the plant? There are two ways. [The
pig eats the plant or the plant dies.] Where are the nutrients now? [In
the pig or in the rotten leaves on the ground.]
4. How do the nutrients get back to the soil? [Rotten leaves go into
the soil or via the pig's faeces or urine.] Do all the plant nutrients
get back to the soil? [No.] Where do they go? [Pigs and tubers go to
the market and some nutrients are lost by leaching.
5. How do you grow more sweet potato and pigs? [By using fertilizer.]
Extra Activity: Make a chart of the nutrient cycle.
6.34a Chemical fertilizers
Be able to explain how chemical fertilizers should be
used.
Use Illustrations and real examples of chemical fertilizers,
technical information, artificial fertilizers.
It is unlikely that children will be using chemical
fertilizers but you can explain. 1. Chemical fertilizers can increase
yields so much that all village gardeners should think about using
them. 2. Chemical fertilizers are expensive because they are all
imported. 3. The use of chemical fertilizers must be exactly as
recommended by the agricultural officers. Otherwise, money will be
wasted. Recommendations are based on type of crop and soil grouping.
Soil Grouping: 1. Coral beach sand soils are weakly weathered,
alkaline, have moderate amounts of phosphorus and low amount of
potassium. 2. Mineral beach sand soils are weakly weathered, weakly
acid, and have moderate amounts of phosphorus and potassium. 3.
Alluvial soils are near rivers or on lower slopes, weakly weathered,
weakly acid or alkaline, with good amounts of phosphorus and moderate
amounts of potassium. 4. Yellowish, brownish, reddish clay soils are
mainly on coral limestone are weathered, acid, with good amounts of
phosphorus but low amounts of potassium. 5. Reddish clays on volcanic
rocks are strongly weathered, acid, low on phosphorus and potassium.
From these descriptions of the soil groupings you can see that most
gardens may not have enough potassium in the soil. You will need a
fertilizer bag. Find out the cost of fertilizer in the local area.
1. Have you seen chemical fertilizer being used? Show the children a
fertilizer bag or packet. Read the label for them. What is the price of
this fertilizer?
2. Explain why these fertilizers are needed but why you should use
them
carefully based on the advice of an agricultural officer.
Extra Activity: See technical information over. Visit a plantation or
project to see the use of chemical fertilizer.
6.35 Burn candle over water, candle burning in
inverted jar over water
See diagram: 20.1.5: Burn candles over water
Be able to observe what happens when a candle burns.
Use glass jars, candles, tray, water, a ruler.
Practice this demonstration before the lesson.
Method 1:
1. Fix a candle to floating cork. Put some water in the tray so that
the water level is about half the length of the candle.
2. Measure the depth of the water in the bucket. Measure the length of
the jar. The jar is full of air so you are really measuring how much
air in the jar. Light the candle.
3. Place the jar over the candle quickly so that the mouth of the jar
is under water.
4. What do you see? [1. The candle flame gets smaller, splutters then
goes out. 2. While the candle was alight, some air bubbles came out
from under the jar. 3. When the flame went out water rose in the jar
and the water level dropped slightly in the bucket. 4. Some water
condensed inside the jar and on the wick.]
5. Why did the candle flame go out? [Some of the oxygen was converted
to carbon dioxide gas. The blackened wick is
carbon ]
6. Why did some air bubbles come out from under the jar? [The candle
flame heated the air in the jar causing the air to expand.]
7. Why did the water move up the jar? [When the candle flame went out
the gases in the jar cooled and contracted to a smaller volume than
before so the air pressure in the jar was less than the atmospheric
pressure. The air pressure on the surface of the water in the bucket
pushed the water up into the jar.]
2 Repeat the experiment with one, two and three happy birthday
cake candles
1. Fix the candles to Plasticine at the bottom of the tray then do the
experiment as before
2. The air in the jar is less heated with smaller candles so you
probably do not see bubbles coming out from under the jar. The jars
contained about the same amount of oxygen but the jar with the
three candles showed the greatest water rise because more heat was
produced by the candles in it.
Extra Activity: Why does a candle burn? [When you light a candle wick,
some heat from the burning wick melts the wax at the top of the candle.
The melted wax rises in the wick because of capillary forces and some
of that wax evaporates to form a vapour that rises then burns with a
bright flame.]
6.36 Candle "lava"
Cooling candle wax looks like cooling lava, describe shapes
Be able to observe the shapes formed by falling drops of
molten wax and discuss how molten rock cools.
Use Candles, matches and a safe place to drop the wax.
Find time to do the activities recommended here.
1. Hold a lighted candle about 30 cm above the tray so that a drop of
melted wax falls on the tray. BE CAREFUL!
2. Repeat this procedure several times, holding the candle at
different heights. Observe the cooled drops.
3. From which height did the molten wax spatter the most? The least?
What shape did the cooled wax take?
4. Explain that volcanoes sometimes shoot out molten rock called lava.
Does this experiment explain the cooled shapes of lava from a volcanic
eruption?
Extra Activity: Study a volcano cone. Does the candle wax experiment
help you understand how the cone was formed?
6.36.1 Cooling candle wax, speed of cooling
and
crystal size
See diagram: 23.7.1 Speed of cooling
Be able to discover whether the speed of cooling affects
the size of crystals and then to discuss why rocks have different sizes
of crystals.
Use Small glass tubes, or any other glass container you can
heat, burner, or a candle in a holder, a wooden peg, two glass jars,
naphthalene (moth balls) or crystals of copper (II) sulfate or salt or
sugar, silver foil or paper or cloth.
An igneous rock consists of crystals produced when the
rock cooled from a very hot liquid state. Rocks that formed deep in the
ground such as granite have large crystals. Rock that formed on the
ground after the liquid rock came out of volcanoes, such as basalt,
have small crystals. Rocks formed deep in the ground cool slowly. Rocks
formed above the ground cool quickly.
1. In this lesson you will imitate the cooling of an igneous rock.
2. Fill the two test-tubes with naphthalene to the one quarter mark,
Using the wooden peg, gently heat the test-tubes until the naphthalene
starts to melt.
3. Move the test-tubes about to distribute heat evenly. Then remove
the tubes from the flame and shake gently. Heat a little more, then
shake again. Keep doing this until all the naphthalene has melted, or
dissolve as many crystals as you can in a small amount of warm water.
4. Quickly wrap the test-tube containing the melted naphthalene or
crystal in silver foil to keep it warm. Then stand it in a large
beaker.
5. Rapidly cool the second lot of melted naphthalene or dissolved
crystals in a beaker of cold water.
6. Observe the naphthalene or dissolved crystals in the two tubes and
note carefully the size of the crystals formed. Why the crystals in the
tubes are different sizes. [Larger crystals formed in the tube wrapped
in foil because it cooled more slowly than the tube in the cold water.]
7. What is the relationship between the rate of cooling and crystal
size of igneous rocks? [The slower the speed of cooling the larger the
crystals formed.]
Extra Activity: Can you find rocks that cooled quickly?
6.37 Electric circuit
See diagram: 32.2.1
Be able to set up an electric circuit to light a light
bulb.
Use Torch light batteries, wires, sticky tape, bulbs, bulb
holders.
Electricity can only be generated if there is a complete
circuit. Revise electric circuits before the lesson.
1. Give each group a battery, wires and a light bulb. You must need
some sticky tape to hold the wires on the bulb contacts. Do not show
the children what to do. Light the bulb. Which group can do it first?
Can you tell the other groups how you did it? This is one way of
encouraging the scientific attitude.
2. Look at the torch battery. What do you see at each end? [The top
has a bump marked on it and is marked "+", the bottom is marked "-".
Each end is made of metal.] How did you make the bulb light? [One wire
touches one end of the battery. The other wire touches the other end of
the battery.]
3. Look at the light bulb. What do you see inside the glass bulb? [A
thin twisted wire called the filament.] Is there a metal part? [Yes,
below the glass part.] How did they make the bulb light up? [One wire
touches the bottom of the metal part, the other wire touches the side
of the metal part.]
4. Electricity travels along a path. If the path is blocked, then
electricity cannot keep flowing. The whole path along which the
electricity travels is called a circuit. A broken path is called an
open circuit.
Extra Activity:
1. Break open an old torch battery with the back of an axe. Be careful!
Can you see the 1. cardboard cover, 2. zinc case,. 3. black chemical
which is a sticky powder, 4. a black carbon rod down the centre of the
battery?
6.38 Electricity conductors
See diagram: 32.2.1
Be able to use a test circuit to show which substances are
conductors of electricity.
Use Batteries, bulb holders (not essential), pieces of wire
(30 pieces if bulb holders are used), connecting boards, many items for
testing, e.g. nails, string, wood, plastic rulers, chalk, rubber,
leaves.
1. Use the chalk board diagram to show the children how to set up
their testing circuits. Give out the materials and tell them to set up
their own circuits.
2. Trace the path of the electricity from one end of the battery to
the other through the circuit. Is the pathway complete? [No.] Does the
bulb light? [No.] Put a piece of wire across the break between the two
drawing pins. What happens? [The bulb lights.] Why? [The wire completes
the pathway and allows the electricity to flow through the circuit.]
3. Test each item to see if they will allow electricity to flow by
placing them to touch two drawing pins. How will you know if
electricity is flowing? [The light bulb glows.]
4. Divide the items into two groups. Group 1 contains things that
electricity will flow through, conductors. Group 2 contains things that
electricity will not flow through, insulators. When all the groups have
finished, fill in the table of results on the chalk board.
5. Most metals are good conductors of electricity, e.g. iron, tin, and
copper are used to make wires. Most non-metals do not conduct
electricity, e.g. glass, plastic, clay, rubber, wood, air. They are
called insulators and are used to stop the flow of electricity. Can you
see insulators on an electricity pole? [Yes.]
Extra Activity: List conductors and insulators you can see in a home/
town. Show the children the large white insulators on electric power
poles. Never touch power lines with sticks or the string of a kite.
Sometimes power poles will conduct electricity will conduct electricity
if they are wet so the children should not touch them. If you see power
lines lying on the ground, you should tell people to keep away and
inform local government.
6.39 Electric torch (flashlight)
See diagram: 33.4.1:
Be able to trace the circuit in an electric torch.
Use A torch with metal sides and a torch battery opened with
the back of an axe.
Take a torch to pieces and put it together again.
Show the class the torch, turn it on and off with the sliding switch.
Dismantle the torch. Show the class the different parts: switch, metal
case. Use the arrows to show them how these parts are part of a
circuit. Show the children the opened battery. The electricity comes
from the zinc case when some zinc dissolves in the black chemical. In
the very old batteries so much zinc dissolves that holes in the zinc
case let some chemical leak out. The carbon rod does not dissolve. Why
should the two batteries be in the same direction in the circuit?
[Otherwise they would push electric currents against each other.] Take
out the batteries in a radio. Are they all in the same direction in the
circuit? [Yes.] The electrical strength of a battery is measured in
volts. How many volts in one battery? [1. 5 volts.] If the batteries
are put end to end in the circuit, how many batteries do you need for a
total of six volts? [Four.]
6.40 Hanging magnets
See diagram: 29.1.6
Be able to predict what will happen when hanging magnets
are brought near each other.
You will need: Bar magnets, two for each group, thin
string, pocket compass. This lesson teaches the rule about magnetic
poles: "Like poles repel, unlike poles attract".
1. Tie the string around each magnet and hang them away from each
other. Look at the pocket compass. Are both hanging magnets pointing in
the same direction? [Yes.] Which way are you pointing? [North-South.]
2. Mark the North Pole on each magnet with a piece of chalk. It may
already be marked with red paint or a small hole. Tie the end of the
string of one magnet to the edge of the desk so that it hangs in a
fixed position. Move the North Pole of the other magnet towards the
North Pole of the fixed magnet. What happens? [The North Pole moves
away.] Move the South pole towards the North Pole of the fixed magnet.
What happens? [They move together.]
3. Pull together = attract, push
apart = repel. Draw the following diagram on the chalk board and tell
them whether the poles attract or repel.
Extra Activity: Repeat the last step but have paper or glass between
the magnets. Do you still attract or repel each other? [Yes.] What does
this show you about properties of magnets?
6.41 Make electromagnets
See diagram 32.2.1:
Be able to make an electromagnet.
Use Pieces of insulated wire, nails about 7 cm long,
batteries, pins or paper clips that can be picked up by a bar magnet.
Winding the wire on the nail. The wire must be wound
around the nail in one direction only. It must not be crossed over and
there should be about thirty turns around the nail.
1. Give each group one piece of insulated wire, one long nail, pins
and paper clips. Put the nail near some pins
and see if it is a magnet. Is it a magnet? [No.]
2. Show the class how to wind a piece of wire around a nail. Test the
nail with the wire on it and see if it is a magnet. Is it a magnet?
[No.]
3. Use scissors to cut away one cm of the plastic at each end of
the wire so that the ends are bare. Connect the ends of the wire to the
battery and see if the nail with the wire around it is a magnet now. Is
it a magnet? [Yes.] Pick up some pins with the electromagnet. Now
disconnect the wire from the battery. Is it still a magnet? [No.]
4. The electromagnet is an important part of a petrol engine. When
electric current flows, the magnet is on, when no current flows, the
magnet is off.
Extra Activity:
What happens to the "strength" of your magnet when you use:
1. less turns of wire around the nail? [The magnetic strength is
less.]
2. two batteries instead of one? [The magnetic strength is greater.]