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Experiments on pages 30, 31, 36, 40, 48, 52, 53, 54, 56 and 57 prepared by Tomislav Sencanski
Note: These experiments should be supervised by adults, especially when performed by younger children and when they involve scissors and other sharp or potentially dangerous instruments.
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INTRODUCTION Dear young readers, You have probably already heard the word science. The book before you will help you enter the world of science. It contains simple experiments whose performance does not require much prior knowledge, but only a little imagination and patience. All the equipment you need can be found in the home. By performing these experiments, on your own or with friends, you will learn a little more about basic scientific facts which you run across in every-day life. Little by little, you will begin looking at reality with more knowledge and more joy. All of a sudden you'll say: "What an interesting world!" Practical work will also help you to learn more about yourself. There is no knowledge which is useless.
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CONTENTS WATER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Why do ponds disappear? . . . . . . . . . . . . . . . . . . . . . . . . . 8 How wind dries things . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Can evaporation be stopped?. . . . . . . . . . . . . . . . . . . . . . 10 A fountain in your bathroom . . . . . . . . . . . . . . . . . . . . . . . 11 Which jet of water is the strongest . . . . . . . . . . . . . . . . . . . 12 Does it float or does it sink? . . . . . . . . . . . . . . . . . . . . . . . 13 Liquid sandwich. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Why it is easier to swim in salt water . . . . . . . . . . . . . . . . . 15 Boat powered by liquid soap . . . . . . . . . . . . . . . . . . . . . . . 16 Sugar and soap move objects . . . . . . . . . . . . . . . . . . . . . . 17 Ice needs room. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Ice which sinks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
PLANTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Do plants drink water?. . . . . . . . . . . . . . . . . . . . . . . . . . . . Two-colour flowers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Do plants release water? . . . . . . . . . . . . . . . . . . . . . . . . . . Which leaf preserves water? . . . . . . . . . . . . . . . . . . . . . . . A garden in a bottle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Zigzag roots. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21 22 23 24 25 26
AIR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Can a glass be truly empty? . . . . . . . . . . . . . . . . . . . . . . . Does air have any weight? . . . . . . . . . . . . . . . . . . . . . . . . Paper holds a ruler down . . . . . . . . . . . . . . . . . . . . . . . . . Propeller driven by a radiator . . . . . . . . . . . . . . . . . . . . . . Potato pellets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Potatoes with bird feathers . . . . . . . . . . . . . . . . . . . . . . . .
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28 29 30 31 32 33
HEAT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Can metal be extended? . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Wires can also be extended . . . . . . . . . . . . . . . . . . . . . . . 36 A handkerchief which doesn't scorch . . . . . . . . . . . . . . . . 37 Expand a balloon without blowing into it . . . . . . . . . . . . . 38 A candle-flame consumes oxygen . . . . . . . . . . . . . . . . . . 39 Ribbons show airflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
LOOKING AT CHANGES . . . . . . . . . . . . . . . . . . . . . . . 41 Underwater fountain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . How yeast breathes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Erupting volcano . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Invisible letter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Experimental cabbage . . . . . . . . . . . . . . . . . . . . . . . . . . .
42 43 44 45 46
LIGHT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Mysterious mirror. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Spinning colours merge . . . . . . . . . . . . . . . . . . . . . . . . . . How a periscope works . . . . . . . . . . . . . . . . . . . . . . . . . . . A magnifying glass without glass . . . . . . . . . . . . . . . . . . . How do moving pictures move? . . . . . . . . . . . . . . . . . . . . Paper movies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . How a camera works . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
48 49 50 51 52 53 54
SOUND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 How sound is reflected . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 Telephone without electricity . . . . . . . . . . . . . . . . . . . . . . . 57 Musical bottles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
ELECTRICITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 Dancing under glass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 Electricity in your hair . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 How to separate pepper from salt . . . . . . . . . . . . . . . . . . 62
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WATER ell over one-half of the earth's surface is covered with water oceans, seas, lakes, rivers, streams and ponds. Water can also be found in the soil and in the air. In the areas around the poles and high up in the mountains, a lot of water exists in frozen form - ice. There is also water inside our bodies. If water were to disappear, life would end at once: plants would wilt and all animals and human beings would die. We drink water directly, but we also take it in when we eat fruit, vegetables and meat. We use water for cooking and washing, for construction and in various industries. Water powers turbines which produce the electricity we use in our homes. Ships sail on water. There is endless circulation of water in nature: water evaporates in the form of water vapour, which goes up and then returns as rain or snow. Waterless regions are called deserts, where there are very few living things. Drinking water must be very pure and clean. Its taste comes from minerals dissolved in it. Spring-water is the healthiest and most pure water for drinking. There is a steadily growing number of people on our planet, and this means that the amount of pure water is slowly diminishing. This means that we must protect our water from pollution.
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Why do ponds disappear? After the rain, all trees, the grass and our playground are wet. Once the sun comes out, it all dries quickly. The water in the pond which has dried up has not disappeared - it has just changed its form into water vapour. This experiment will help you to discover how quickly the sun dries out water. You can do it when it's sunny, after rain.
Necessary materials: A piece of chalk
How the experiment is performed 1. Mark the outline of the pond with the chalk. Note the time. 2. Come back once every hour and trace the new outline.
What will happen? You will get a series of outlines showing the speed at which the pond shrank. After a few hours, it will disappear completely.
Why? The heat of the sun warms up the water and speeds up its molecules (tiny particles of which is made). Some of the molecules close to the surface gain enough speed to be able to break free of the others and evaporate into the air. The warmer the water, the quicker the evaporation will be. You can see that all the water boiling in a saucepan will be able to evaporate in just a few minutes.
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How wind dries things The wind helps wet things to dry out, as the following experiment will show.
Necessary materials: cotton cloths approximately 50 by 50 centimetres, clothes-pegs
How the experiment is performed
1. Soak all the cloths in water, but don't wring them out. 2. Hang them on clothes-lines in various spots: in the shade where there's no wind, in the shade where it's windy, in the sun where there's no wind and in the sun where it's windy. You can also hang some to dry inside the house. Spread them out well.
What will happen? The cloth in a windless and shady spot will take the longest to dry. Conversely, the one in a sunny and windy spot will dry out the fastest. Stretching the cloth out properly also helps reduce drying time.
Why? We saw in the preceding experiment how the sun helps evaporation. Wind is also important in this process, because it helps carry water molecules away from the surface of the cloth.
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Can evaporation be stopped? Water constantly evaporates from the seas, lakes, rivers and ponds. But it is possible to stop evaporation, which we shall show by this experiment.
Necessary materials: a saucer, water, a small glass, a felt-tipped pen and a large plastic bowl.
How the experiment is performed 1. Draw a line half-way up the glass. 2. Fill with water up to the line. 3. Pour the water from the glass into the saucer. Now pour more water into the glass up to the line. In this way there will be equal quantities in both the glass and the saucer. 4. Cover the glass with the bowl and leave the saucer outside the bowl. Leave them untouched for a day.
What will happen? Most of the water in the saucer will have evaporated, while the level of the water in the glass will remain unchanged.
Why? Water evaporates when it is in contact with air. If that contact is prevented, there will be no evaporation and the water molecules closest to the surface simply have nowhere to go.
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A fountain in your bathroom You have probably seen many fountains from which jets of water fly up into the air. You can try to make something similar in your garden or bathroom.
Necessary materials: a plastic hose, a funnel, adhesive tape, a pin, some water
How the experiment is performed 1. Fix the funnel to one end of the hose, and seal off the other end with the tape. Punch a hole in the tape with the pin. 2. Hold the hose in the manner shown at right and pour water into the funnel. 3. Once the hose is full, slowly lower the taped end. Water will begin streaming from the little hole. 4. Keep lowering the taped end.
What will happen? As you lower the end of the pipe, the water jet will increase in strength, forming a small fountain.
Why? The higher the pillar of water above the opening, the stronger the pressure of the water. A certain level of pressure is needed for water to reach our kitchen and bathroom taps. This pressure is obtained by pumping water into high towers, which are connected to our bathrooms and kitchens by a large system of pipes.
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Which jet of water is the strongest The previous experiment showed us how the strength of a jet of water depends on the height of the pillar of water above it. In this experiment, we shall make a fountain with jets of water of different strengths.
Necessary materials: A cardboard tube, plasticine, water, a spike
How the experiment is performed 1. Us the spike to make four small equally-spaced holes along the cardboard tube. 2. Seal one end tightly with the putty. 3. Pour water into the tube.
What will happen? The flows of water from the holes will be different.
Why? The pressure of the water in the topmost hole is the smallest, hence the jet will be the weakest. The jet from the bottom hole will be strongest, because the pressure here is the biggest.
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Does it float or does it sink? Does plasticine sink or does it float? Wood, Styrofoam and ice float on water regardless of their shape and size. But materials like plastic putty or metal sometimes float and sometimes sink. This depends on their shape, which we shall show in this experiment.
Necessary materials: a lump of plasticine, four glass marbles, a vessel with water
How the experiment is performed 1. Put the marbles in the water and they will sink at once. The same will happen to the plasticine lump. 2. Now take the marbles and the plasticine out. Form the plasticine into a round and shallow pan. 3. Lower the plasticine pan into the water.
What will happen? The plasticine will float. You can put the marbles into it, but it will still float on the water.
Why? A kilo of water takes up more space than a kilo of plasticine. This means that the plasticine is heavier and more dense than the water and will sink in it. But once you shape it as a boat, the plasticine is "filled" with air. Taken together, the plasticine and the air are lighter and less dense than the water, and the boat will float.
Additional idea Measure out several equal chunks of plastic putty. Organise a competition: who can make a boat which will take the biggest number of marbles without sinking?
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Liquid sandwich Many liquids are similar to water and can be mixed with it easily. But there are also those which are very difficult to mix with water. One of them is oil.
Necessary materials: water (coloured with some ink), oil, glycerin, a bottle with a stopper.
How the experiment is performed 1. Pour equal quantities of oil and water into the bottle. 2. Close well and shake vigorously.
What will happen? The liquids will mix, but not for long - soon the oil will be floating on top of the water.
Why? Oil and water refuse to mix because their densities are different. This means that their weights also differ: oil is lighter, so it floats on top of the water.
Additional idea Try adding another liquid. Pour in the densest liquid first, for example glycerin.
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Why it is easier to swim in salt water? We have already seen that all liquids have their own specific densities. The denser (or "heavier") the liquid, the better things can float on top of it. Have you heard of the Dead Sea? Its density is a result of a very high content of salt. In the Dead Sea, you don't need to keep swimming to keep yourself on the surface. The following experiment will show you that it is easier to float in a denser liquid.
Necessary materials: a drinking straw, plasticine, container with ordinary water, container with salty water.
How the experiment is performed 1. Fix a plasticine ball to one end of a drinking straw. 2. Lower the straw into a container with ordinary water until it floats upright. 3. Mark the water level on the straw. 4. Now do the same in a vessel filled with salty water.
What will happen? The straw will sink deeper into the fresh water.
Why? The particles in a denser liquid are bigger or closer to one another than those of less dense liquids. Denser liquids exert more pressure on objects on their surface. In the case of the Dead Sea, the very salty and very dense water exerts pressure on swimmers, preventing them from sinking.
Additional idea Pour some more salt into the vessel and repeat the experiment. Is there any change?
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Boat powered by liquid soap Make an unpowered boat which will nevertheless be able to move.
Necessary materials: a clean pan filled with water, greased paper, some liquid soap, a ruler, scissors, a pencil
How the experiment is performed 1. Draw an equal-sided triangle on the paper with a base of about 4 to 5 centimetres and a height of 8 to 9 cm. 2. Cut out the triangle and place on the surface of the water. 3. Put a drop of liquid soap on a fingertip. 4. Immerse the fingertip into the water behind the triangle's base.
What will happen? The "boat" will move.
Why? The force between molecules on the surface of the water is bigger than that inside the vessel, forming surface tension. The surface of the water acts as a tight membrane. As the soap dissolves, it emits oil residues into the water. These residues weaken the surface tension and push the boat away from the spot where your finger touched the water.
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Sugar and soap move objects Soap can "force" objects to move on the surface of water. Sugar can do the same, but the movement is different. Let's check.
Necessary materials: A bowl of water, matchsticks, a sugar cube, a piece of soap
How the experiment is performed 1. Break the matchsticks into smaller pieces and allow to float on the water. 2. Put the sugar cube into the centre of the bowl. 3. Now put the piece of soap into the centre of the bowl.
What will happen? The sugar will move the pieces of wood towards the centre. The soap will move the pieces away from the centre.
Why? Sugar is porous and draws water into itself, pulling the pieces of wood along in the current it thus creates. As we have seen in the preceding experiment, the soap dissolves and emits oil residues, which weaken the surface tension of the water and propel the pieces away from the centre of the bowl.
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Ice needs room Cooled sufficiently, water turns into a solid form called ice. When that happens, it occupies more space than that taken up by liquid water. Let's prove this.
Necessary materials: water, aluminium foil, a funnel, a freezer, a small glass bottle
How the experiment is performed 1. Using the funnel, fill the bottle with water completely. 2. Place a piece of foil on the top and put the bottle into the freezer. 3. Take out of the freezer after several hours.
What will happen? The ice will lift the foil, showing that the water expanded as it froze.
Why? Most liquids get denser as they freeze, but water does the opposite - as it turns into ice, it gets less dense and takes up more space. Ice floats on water because water is denser than ice. Icebergs bloat on the oceans for the same reason. Attention: Be careful, as the bottle could crack during the experiment.
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Ice which sinks We shall show that ice can sink into water, even if only for a short while.
Necessary materials: an ice tray, a freezer, water colours, a plastic glass
How the experiment is performed 1. Pour some water into the plastic glass and colour with a water colour. 2. Pour the coloured water into the ice tray and place in the freezer. Let freeze. 3. Pour some hot water into the plastic glass. 4. Put a cube of the coloured ice into the glass.
What will happen? As the cube melts, the colour will spread through the hot water. The cube will sink to the bottom of the glass, but after some time it will once again rise to the surface.
Why? As the cube melts, its density increases and it sinks to the bottom. There, it is warmed by the hot water, its volume increases and its density decreases, so it rises to the surface again.
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PLANTS ry and imagine what life on our planet would be like without plants. Besides being used as a food source for human beings and most animals, plants also affect the air, the soil, the weather and other things. Without them, no other living thing would be able to survive. For their development, plants need soil, water, air, sunlight and heat‌ Al things are inter-connected in nature.
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Do plants drink water? Water reaches plants from the soil - it enters through their roots and moves up through their stems. This experiment will show how.
Necessary materials: White flowers (for example carnations or roses), water coloured with some ink or food dye
How the experiment is performed 1. Put the flowers into the coloured water. 2. Allow to stay for a day.
What will happen? The flowers will show traces of the colour of the water.
Why? The flower's stalk contains tiny tubes called capillaries. When immersed into water, the molecules of the capillary walls which are in contact with the water attract the water molecules which are the closest to them and raise them above the level of the water in the vessel. To this capillary phenomenon should also be added the osmotic pressure which takes the water all the way up to the top of the flower.
Additional idea: Try the experiment using various food dyes. Which gives the best results?
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