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To m i s l a v S e n ć a n s k i

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INTRODUCTION This is the third in a series of books about experiments you can do at home which will help you to take a step closer to science. All three SIMPLE SCIENCE EXPERIMENTS books are intended for young readers, especially primary schoolers. Most of the experiments fit in with the physics curriculum: there is one or more experiments for each area covered by it. The experiments have been carefully chosen for performing at home. They are easy to do, interesting and convincing. Best of all, they will help you to understand what you are learning in school. Every experiment that is performed successfully helps to increase interest in doing others. If you manage to complete most of them, science will be near and dear to you for the rest of your life. Like the preceding volumes, SIMPLE SCIENCE EXPERIMENTS is certain to justify its presence in your home library. The author


CONTENTS THE PROPERTIES OF OBJECTS How to make cardboard tougher . . . . . . . . . . . . . . . . . . . . . . . . . Which ice is harder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Inertia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stubborn dominoes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Coloured chalk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7 8 9 10 11

FORCE Muscle force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . One is stronger than two . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The can that "flees away" from water . . . . . . . . . . . . . . . . . . . . . . . A self-propelled box . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Which falls faster? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

12 13 14 15 16

PRESSURE Coins pierce putty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lifting a glass of water with the palm of your hand . . . . . . . . . . . . The moving test-tube . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The water fountain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Now it flows, now it doesn't . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Make a spray jet from a drinking straw . . . . . . . . . . . . . . . . . . . . . How a pontoon works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The diver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . An unusual cup holder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

17 18 19 20 21 22 23 24 25

HEAT Nails thicken as they are heated . . . . . . . . . . . . . . . . . . . . . . . . . . The jumping coin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Self-adhesive ice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Salt melts ice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Heat versus margarine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Black and white . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

26 27 28 29 30 31

ENERGY The roller that comes back . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The forehead as a thermometer . . . . . . . . . . . . . . . . . . . . . . . . . . A pendulum swings a pendulum . . . . . . . . . . . . . . . . . . . . . . . . . .

32 33 34

ELECTRICITY Raising your hair on end . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Remote-control with a stick . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

35 36


Pantyhose electroscope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lightning from a spoon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

37 38

ELECTRIC CURRENT Electricity can heat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Batteries as magnets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Light-bulbs change intensity . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

39 40 41

MAGNETS Make a magnet from iron filings . . . . . . . . . . . . . . . . . . . . . . . . . . Reversed roles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

42 43

LIGHT Green is not always green . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mixing colours . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A sundial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . How a ray of light is reflected . . . . . . . . . . . . . . . . . . . . . . . . . . . . Floating in the air with the help of a mirror . . . . . . . . . . . . . . . . . . How to bend light rays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Multiple images of a single object . . . . . . . . . . . . . . . . . . . . . . . . . Get your correct image in a mirror . . . . . . . . . . . . . . . . . . . . . . . . Water as a lens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . False images in glasses of water . . . . . . . . . . . . . . . . . . . . . . . . . . Caleidoscope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A mini-cinema at home . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . How to find your blind spot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . How to make a rainbow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

44 45 46 47 48 49 50 51 52 53 54 55 56 57

CHEMICAL REACTIONS Burning metal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Restoring lustre to aluminium . . . . . . . . . . . . . . . . . . . . . . . . . . . . A salt garden . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Soap bubbles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Making glue from potatoes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Launching a cork . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

58 59 60 61 62 63

OBSERVING CHANGES How to get at egg into a bottle . . . . . . . . . . . . . . . . . . . . . . . . . . . How to blow up an egg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fresh or cooked? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The magic matchsticks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . How to cheat a scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air scales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A cloud inside a bottle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A pine cone as a barometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

64 65 66 67 68 69 70 71


THE PROPERTIES OF OBJECTS Every object has certain properties: hardness, colour, taste, smell, density, volume, inertia‌ Some of these properties change on their own, while we are able to alter others. It is easy to change the properties of cardboard and ice - the following experiments will show you how.

You need:

HOW TO MAKE CARDBOARD TOUGHER

How the experiment is performed: 1. Place two of the glasses apart by the width of the third, and the cardboard across them. 2. Place the third glass in the middle of the cardboard. 3. Now repeat the experiment, but first fold the cardboard in an accordion shape. Why? When the cardboard is folded, many more particles (molecules) participate in holding up the glass.





Three identical glass tumblers A piece of thin cardboard

What will happen: In the latter case, the cardboard will hold up the glass. Additional idea Crumple and squeeze a newspaper page as hard as you can. You will see that the further you go the more difficult it becomes.

7


You need:

WHICH ICE IS HARDER



 

How the experiment is performed: 1. Pour a little water into both cups. 2. Put some sawdust into one of them, and make sure the water levels in both are equal. 3. Let both boxes freeze well in a freezer. 4. Now try to break the two ice disks.

What will happen: The ice with the sawdust will be harder to break. Why? The sawdust acts as a reinforcement which makes the ice tougher.

8

Two round plastic containers (old butter or margarine cups) sawdust water


You need: 

Thin paper ribbons

You need:

INERTIA

Thin paper ribbons a thin wooden lath (about 3 mm thick)  glue 

Objects have a tendency to preserve their state of rest, which we can prove by this experiment. How the experiment is performed: 1. Use the glue to make hoops of the ribbons. 2. Get two friends to hold up the hoops with the lath hanging across, as shown. 3. Chop the lath in the middle with your hand.

What will happen: The lath will snap while the paper hoops will stay intact.

Why? Due to their inertia, the hoops will remain at rest and will not break - as you might have expected them to do

Additional idea: Place a ping pong ball on the rearmost end of a roller-skate, and push it towards a wall. When the roller-skate hits the wall, it will stop, but the ball will continue moving forward due to its inertia.

9


You need:

STUBBORN DOMINOES



Eight dominoes

How the experiment is performed: 1. Arrange the dominoes as shown in the picture. 2. Place the last domino outside, as shown, and your index finger on its corner. 3. Push down hard on the domino to flip it backwards and to make it drive out the lowest horizontally-placed domino. What will happen: The horizontal domino is expelled, but the construction does not crumble.

Why? Due to inertia, the whole assembly retains its position. Note that you need a little practice to make this experiment work well. 10


You need:

COLOURED CHALK If you need coloured chalk and you only have white, how can you colour it?



white chalk



food dyes water



How the experiment is performed: 1. Dissolve the dyes in lukewarm water. 2. Place the chalk in the water and let it stay there for a while. 3. Take the chalk out and let it dry. What will happen: The white chalk will become coloured chalk. Why? Chalk is hygroscopic: it absorbs liquids easily because it is porous - it is full of capillaries which water enters very easily. As the water then evaporates, it leaves behind traces of the dye.

Additional idea: Try to colour the chalk using permanganate (mouthwash solution).

11


FORCE Force is the strength or power exerted upon an object by another object. We cannot see force itself, but we can see its effect. In order for an object to be moved from a state of rest or to be stopped, a force must be exerted on it. You need:

MUSCLE FORCE All people exert force by using the strength of their muscles. If you have a dynamometer - a spring scale - you can measure your own muscle strength in the following way.

 

 

a spring scale a bottle and a cork stopper a corkscrew a piece of cord

How the experiment is performed: 1. Loop one end of the cord around your foot and attach the other to the dynamometer. 2. Pull the dynamometer upwards.

What will happen: The pointer on the dynamometer moves and shows the force that you are exerting.

Why? The dynamometer works on the principle of an elastic spring - the stronger the force, the more the spring is extended and the further it moves the pointer. You can also measure the force needed to extract a cork from a bottle, as shown at right. Additional idea: Pull apart an expander's springs as far as you can and measure the distance you have achieved. In that way you and your friends can compare your strengths.

12


You need:

ONE IS STRONGER THAN TWO



Two wooden sticks of circular section



strong fabric ribbon of about 3.5 meters in length

How the experiment is performed: 1. Two boys should face each other and hold the sticks as shown. 2. The third boy should tie one end of the ribbon to one stick and then make three twists of the ribbon around the sticks. 3. Each of the two boys then pulls the sticks as hard as he can towards himself, while the third pulls the free end.

What will happen: The third boy will pull the sticks together very easily.

Why? The sticks and the ribbon form a tackle - a simple mechanism or apparatus used for lifting and lowering heavy objects. The force exerted by the third boy is about one-fifth of that exerted against him by the other boys - this depends on the number of turns around the sticks.

13


FORCES OF ACTION AND REACTION There are many experiments which show the forces of action and reaction at work.

T KHoEn zCeArNv aT HkAoTj a" F L E E S AWAY" FROM WATER

You need: 

an empty tin can



a suitable vessel with water some string a hammer and a nail

 

How the experiment is performed: 1. Using the hammer and nail, pierce two holes opposite each other just below the lip at the open end of the can. 2. Make two or three somewhat larger holes close to each other near the opposite end of the can. 3. Suspend the can with the string as shown. 4. Holding over a bathtub, pour water into it slowly.

What will happen: The can swings away from the direction in which the water flows out of it. Why? The cause of the can's movement is the reactive force caused by the outflow of water. NOTE Ogled izvoditi iznad kade ili lavaboa.

14


You need: 

a rubber balloon



a cardboard box without a lid marbles two wooden rails (bars) string a clothes-peg scissors

A SELF-PROPELLED BOX  

How the experiment is performed: 1. Place marbles between the two rails as shown. 2. Make one bigger hole on the box for the balloon's opening and two smaller ones opposite each other for the string, as shown. 3. Place the balloon in the box and thread its end through the bigger hole. 4. Blow up the balloon and seal the opening with the clothes-peg. 5. Tie the string across the balloon as shown, to keep it inside the box. 6. Place the box between the rails and remove the peg.

Why? The air escapes from the balloon (action), and the box moves in the opposite direction (reaction).

15

  

What will happen: The box starts to roll over the marbles.


You need: 

WHICH FALLS FASTER?



a metal plate an sheet of paper of the same size

Iz ovog ogleda mo`emo zakqu~iti kako otpor vazduha deluje na padawe tela. How the experiment is performed: 1. Holding them horizontally, let the metal plate and the paper fall at the same time. 2. Now place the plate over the paper and let them fall together.

What will happen In the first case the plate will reach the floor first, and in the second they will arrive together. Why? The metal plate and the paper both fall under the influence of the Earth's gravitational force, but in the first case the plate falls faster because it has an easier time forcing its way through the resistance of the air. In the second case the plate and the paper encounter the same resistance, just as if they were in a vacuum where there is no air resistance and where the only force acting on them is gravity.

16


PRESSURE Pressure arises when a force acts on a surface. The weight of an object is one form of pressure, so that objects exert pressure on the surface on which they are resting by their weight. Pressure is also exerted by liquids, both still and moving. All living and other things are exposed to atmospheric (air) pressure. Here are a few simple experiments to show us how pressure acts and what it can be used for. You need:

COINS PIERCE PUTTY





How the experiment is performed: 1. Place one coin flat on the putty and press down on it with your finger. 2. Now place the other coin on its edge and repeat the experiment. What will happen: The second coin will sink into the putty much deeper.

Why? The area of the second coin acting on the putty is much smaller than that of the first, therefore the pressure it is exerting is also higher and it sinks deeper into the putty.

17

two identical coins some plasticine putty


You need:

LIFTING A GLASS OF WATER WITH THE PALM OF YOUR HAND



A plastic cup full of water

Make a bet with your friends that you will be able to lift a cupful of water with the palm of your hand on top of it. What will happen: The cup will stay attached to the palm of your hand.

How the experiment is performed: 1. Place the cup on the table. 2. Moisten the palm of your hand and press down flat on the cup, holding your fingers bent, as shown. 3. Now straighten your fingers, but continue to press down on the cup. 4. Lift you hand slowly.

Why? By pressing down on the cup you expel a little air. This makes the outside air pressure stronger from that of the rarified air inside, and that it what holds the cup attached to your hand.

18


You need: 

THE MOVING TEST-TUBE Test-tubes can rise up like rockets. This is how:



Two test-tubes of unequal size (the smaller to fit snugly in the bigger) some water

How the experiment is performed: 1. Pour water into the larger test-tube and then insert the smaller one so that it forces out a little water. 2. Now turn them upside-down, as shown. What will happen: The water will drip down between the two tubes while the inner one will slowly rise.

Why? The water which flows out is replaced by air which gradually fills the test-tube and forces it upwards.

19


You need: 

THE WATER FOUNTAIN 

Make a fountain in your room.

  

two bottles, one full of water and the other empty a cork stopper a long plastic drinking straw a thin drill bit plasticine putty

How the experiment is performed: 1. Drill a hole for the straw through the cork lengthwise. 2. Plug the empty bottle with the cork and insert the straw. 3. Use the putty to seal any gap that might exist between the straw and the cork. 4. Suck some air from the bottle and quickly seal the straw with your finger. 5. Turn the bottle upside down and place it on top of the bottle with water, inserting the end of the straw into the water. What will happen: Water will come out of the straw like a small fountain. Why? The pressure exerted by the outside air on the water in the lower bottle is higher than that of the air in the upper bottle, causing a difference in pressures which forces up the water.

Additional idea: Look at the picture on the right. Insert two bent straws through the cork as shown, one long enough to dip down into the water. Now blow into the other straw. As you blow through the shorter straw, water will flow out of the bottle through the other one.

20


You need: 

NOW IT FLOWS, NOW IT DOESN'T Air pressure can both prevent and help water to flow out of a bottle. Let us see how

 

a plastic bottle a needle  a suitable vessel with water

How the experiment is performed: 1. Pierce a number of small holes in the bottom of the bottle. 2. Immerse the bottle in the water vessel to fill it. 3. Plug the opening with you thumb and take the bottle out. What will happen: The water will not flow out of the little holes. Why? Due to the pressure of the air on the holes. When you remove your thumb the water will begin to flow - this time the pressure being exerted on it is both that of the water itself and of the air. Use these bottles as watering cans.

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Simple Science Experiments 3  

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