Science Experiments

This is what your experiment should look like1 Cut some absorbent paper (such as paper towel) into strips about 2 cm wide The length isnt really

important and will depend on the size of the jar you hang them in2 Draw a small circle 1 cm from the bottom of the paper with different black markers or felt-tipped pens3 Fill a clean jar with about 1 cm of water and carefully place the paper into the jar making sure that the

bottom of the paper is in the water The circle must be ABOVE the water level Use paper clips to hold the paper upright in the jar Watch the water rise up the paper

4 After a few minutes remove the paper from the jar Notice how different colours in the ink travel up the paper at different speeds

5 Now try some different colour pens and markers Can you see any differences6 Did you have any pens for which the ink did not separate If so repeat the experiment using methylated

spirits instead of water in the jar Try out a variety of pens Can you see any differences The method used to compare inks is called chromatography It involves separating the ink in each of the pens As the solvent (water) rises up the paper the different colours of the ink separateAsk your family to play your suspects Have them use specific pens for the job and see if you can figure out which ink comes from which pen and nab your suspect

WHAT YOU NEEDTo do this experiment you will need

cornflour food colouring a small mixing bowl water

WHAT TO DO1 Pour some cornflour into a mixing bowl2 Stir in small amounts of water until the cornflour has become a very thick paste3 To make the slime the colour of your choice thoroughly stir about five drops of food colouring into the

mixture4 Stir your slime REALLY slowly This shouldnt be hard to do5 Stir your slime REALLY fast This should be almost impossible6 Now punch your slime REALLY hard and fast It should feel like youre punching a solid

You can keep your cornflour and water mixture covered in a fridge for several days If the cornflour settles you need to stir it to make it work well againWHATS HAPPENINGAnything that flows is called a fluid This means that both gases and liquids are fluids

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Fluids like water which flow easily are said to have low viscosity whereas fluids like cold honey which do not flow so easily are said to have a high viscosityCornflour slime is a special type of fluid that doesnt follow the usual rules of fluid behaviour When a pressure is applied to slime its viscosity increases and the cornflour slime becomes thickerAt a certain point slime actually seems to lose its flow and behave like a solid Cornflour slime is an example of a sheer-thickening fluidThe opposite happens in sheer-thinning fluids they get runnier when you stir them or shake

them up For example when toothpaste is sitting on a toothbrush it is pretty thick so you can turn the toothbrush upside down and the toothpaste doesnt fall offBut if it was that thick when you tried to squeeze it out of the tube there is no way you could manage it Fortunately toothpaste gets runnier when you are squeezing it out of the tube Other sheer-thinning fluids include

blood paint ballpoint pen ink nail polish

Although there are lots of sheer-thinning and sheer-thickening fluids nobody has a really good idea why they behave the way they doThe interactions between atoms in the fluids are so complicated that even the worlds most powerful supercomputers can not model what is happening This can be a real problem for people who design machinery that involves sheer-thinning fluids because it makes it hard to be sure if they will work

WHAT YOU NEEDTo do this experiment you will need the following

a helper a tin container with a tin lid such as a coffee tin four long pencils a metal bottle cap (a soft drink bottle cap is less effective) strong sticky tape adhesive putty (Blu-Tack or similar)

WHAT TO DO

diagram of the Cracking Fun experiment1 Fill the container with water until it is overflowing and press the lid on2 Place the metal bottle cap on the centre of the lid and secure it with a small piece of adhesive putty3 Place three of the pencils next to each other on the table and tape them together to make a flat platform4 Rest the container on the pencil platform so that the pencils poke out on both sides

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5 Place the fourth pencil on top of the bottle cap and fasten it with a bit of adhesive putty6 As one person holds all the pieces together use strong tape to strap the top pencil tightly to the pencil

platform on either side of the tin and then place in the freezerHave a look after 24 hours (if you have used a large container it may take 48 hours) Marvel at the power of iceWHATrsquoS HAPPENINGWater is one of a few chemicals that expands when it changes from liquid to solid As water cools it contracts like any other substance ndash the molecules slow down they have less energy and get closer togetherBut as its temperature drops below four degrees Celsius water begins to expand The molecules begin forming stiff bonds with their neighbouring molecules which push them outwards to form a hollow structure or crystal lattice which can float in liquid waterAs water freezes and expands it can exert incredible pressure For example it has enough energy to burst open the walls of plant and animal cells crack rocks burst water pipes and crack your pencilPlant and animal cells contain water As this water turns to ice the cells expand causing them to burst In mountain and polar explorers such burst cells can cause frostbite which is an irreversible condition Also severe damage to fruit and vegetable crops can occur when sudden cold snaps cause plant cells to burstAPPLICATIONSPeople in cold climates need to add anti-freeze to the coolant in their motor vehicles The anti-freeze lowers the freezing point of the coolant beyond the coldest temperature that the vehicle will be exposed to This means that the coolant does not freeze solid and cause damage to the engineSome people believe that they can lsquocheat deathrsquo by having themselves cryogenically frozen The idea is that if you die from an incurable disease such as cancer and have yourself frozen you can be re-animated in the future once people discover a curePeople who are cryogenically frozen are kept at temperatures well below -196deg Celsius using liquid nitrogen If they were to be placed straight into liquid nitrogen all the cells in their body would freeze and burst To prevent damage to the cells all the water in the body is removed and replaced with a glycerol-based mixture called cryoprotectant which is similar to antifreezeSo far dozens of people have been cryogenically frozen but no one has been reanimated ndash the technology to do so is yet to be discovered

WHAT YOU NEEDTo do this experiment you will need the following items

a large glass jar with a lid a thin piece of string Blu-Tack (or similar) a sugar crystal 1 - 2 kg of sugar food colouring (optional) a saucepan

WHAT TO DO

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diagram of the Crystal Grower experiment1 Drill or punch a small hole through the lid of the jar (you may need an adult to help you) Thread the

string through the hole Secure the strand with a small ball of Blu-tack covering the top of the hole or alternatively tie a knot above the hole Tie a good-sized sugar crystal (seed crystal) to the other end of the string

2 Place frac34 cup of water in the saucepan bring it to the boil then reduce to a simmer Pour sugar into the hot water until no more sugar will dissolve If you do not add enough sugar the solution will not become super-saturated Turn off the heat and allow the sugar solution to cool Dont touch or move the saucepan as the sugar solution will be extremely hot

3 Once the solution is cold pour it into the jar until it is approximately frac34 filled Poor the remaining solution into a spare container for later Secure the lid ensuring that the strand and sugar crystal are in the solution

4 Place the jar in a cool location such as a cupboard Check the crystal each day If the crystal hasnt grown for a day or two replace the solution with remaining sugar solution or make some more in a saucepan The crystal needs to sit in a super-saturated solution to continue growing Time and patience are required because crystals are slow growing The crystals in the photo at the top of this page were growing for about a month You may want to leave yours to grow for more than a month The crystals will eventually reach a point where they will stop growing

Once your crystal has become large enough you can remove it from the stringFor added flair add food colouring to the water to create colourful crystals (A small drop of the colouring is sufficient)WHATS HAPPENINGA solution is a mixture of a solute and a solvent In this example the solute is sugar and the solvent is water If you add a small amount of solute to the solvent typically the solution is under-saturated Adding more solute will cause the concentration of the solution to increase until you cannot dissolve anymore solute The solution is now called saturatedBy heating the solution it is possible to dissolve more solute making the solution super-saturated This is an unstable state for the solution and as soon as conditions change (for example the temperature lowers) some of the solute will reappear in solid form - precipitationTo precipitate the dissolved solute looks for a seed to build upon In the case of our experiment it uses the sugar crystal Over time more of the solute precipitates on the outside of the seed layer upon layer forming a larger crystal Once the solution returns to a saturated state the crystal stops growingCreating a seed crystalIf you need a seed crystal large enough to tie on the end of your string heres an idea Half fill a jar with water from the tap and stir in a few tablespoonfuls of sugar until the solution is saturated Tie a piece of string to a

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pencil and balance it over the top of an open glass jar with the string hanging in the sugar solution Place the jar in a sunny position and within a few days you should have a number of good-sized seed crystals

WHAT YOU NEEDTo do this experiment you will need the following

a tall glass or plastic container some vegetable oil ice (try adding some food colouring to make it easier to see)

WHAT TO DO1 Fill the glass with oil2 Drop a block of ice into the glass The ice should float in the middle of the oil3 Watch the ice as it melts

You will find drops form on the ice then drop off to fall slowly through the oil As the drops form and fall the ice will rock from side to side and move up and downWHATS HAPPENINGThis activity is all about density The density of a material is how much a given volume of that material weighs For example one cubic metre of liquid water weighs 1000 kg so it has a density of 1000 kgmsup3When you drop an object into a liquid it feels the forces of

gravity which pulls it down buoyancy which pushes it up

When you drop something into a liquid it displaces some of the liquid (pushes it out of the way) An object placed in a liquid feels an upward force equal to the weight of the liquid it is displacing This force is called buoyancyIf the weight of the object is less than the weight of the liquid it is displacing it will float If it is greater it will sink Another way to say this is that if the object is less dense than the liquid it will float but if it is denser it will sink This is even true for liquids Liquid water is denser than oil so the oil floats on the waterWater is weird stuff We dont normally notice it because water is so common but water does some things that almost no other chemical will do One of the ways water is strange is that it is less dense as a solid than as a liquidIce and vegetable oil have almost the same density around 920 kgmsup3 so a block of ice dropped into oil will barely move As the water melts it turns into denser liquid water The water tends to stick to the ice for a while before it drops off If there is enough liquid water on the ice then the density of the ice and water together is greater than the oil so they will sink Once the drop of water falls off the ice the ice floats up againIts a good thing that ice floats on water In winter some rivers and lakes freeze on the surface If ice was denser than water then the rivers and lakes would freeze from the bottom up which would kill plants growing in them and starve most of the fish and other marine life

WHAT YOU NEEDTo do this experiment you will need the following items

a tall clear jar or PET bottle golden syrup or honey water oil screws paperclips and any other small objects ice cubes

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food colouring detergent

WHAT TO DO1 Carefully pour some golden syrup water and oil into the container in that order You might want to add

food colouring to the different layers to be able to see them better What do you see2 Drop in the small objects Do they reach the bottom Try dropping in the ice-cubes3 Add a drop of detergent What happens

WHATrsquoS HAPPENING

Diagram of the Density Column experimentGolden syrup water and oil have different densities so they donrsquot mix Instead they form three different layers The denser fluids sink to the bottom while less dense fluids rise to the top Where other objects sit in the density column depends on how dense the objects areTemperature can affect the density of fluids and solids The strange thing about ice is that it is less dense than water so it floats in the oil level However cold water is denser than warm water Try adding a few droplets of colouring to half a cup of very hot water (ask an adult to help you) and add it to your density column Does the colouring mix with all the water or does the hot coloured water form another layerEver wondered why you need detergent for washing up your dishes Normally oil and water donrsquot mix together When you add soap or detergent it reduces the surface tension of water allowing it to dissolve the oil Adding a few drops of detergent wonrsquot be enough to dissolve all the oil in your density column However you should be able to see lsquobreaksrsquo in the layers where some of the oil dissolved in the water

Turn a margarine container into a balloon-powered jet boat Its easyWHAT YOU NEEDTo do this experiment you will need to gather

a margarine container a balloon a straw a rubber band plasticine scissors something that will pierce the margarine container to make a hole big enough to fit a straw through

WHAT TO DO

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1 Find a clean rectangular margarine container and carefully make a hole in the centre of one of the

shorter sides about 1 cm from the bottom2 Cut a straw in half and insert one end into the neck of a balloon Fix the balloon firmly to the straw with a

rubber band3 Push the straw through the hole in the marg container and seal it in place with plasticine Weigh the back

of the marg container with more plasticine in the centre Blow the balloon up through the straw and pinch the end to keep the air inside

4 Put the boat in the water let go - and away she goesThis is an example of Newtons third law of motion - every action has an opposite and equal reaction The air rushing out of the straw is the action and the equal reaction is the push against the boat in the opposite directionCan you improve the design of your boat

Who needs a beach when you can surf on balloons Try this activity at home or at school WHAT YOU NEEDTo do this experiment you will need to gather

an adult assistant balloons an upside-down desk or some other flat-bottomed object that can survive you standing on it a carpeted floor a table pole or wall you can use to help yourself balance

WHAT TO DO1 Check that there is nothing sharp on the desk or floor that could damage a balloon2 Half-inflate four balloons and tie them off3 Place the balloons under the corners of the desk4 Have your assistant hold the desk still They shouldnt try to take the weight just help keep it balanced

Make sure they do not put any of their fingers under the desk - they might get squashed5 Carefully step up onto the desk You can use another table or a pole to help you balance as you climb up

Unless something sharp bursts them the balloons should be able to support your weightIf there are other people around you could try testing to see how many people the balloons can support

WHAT YOU NEEDTo do this experiment you will need to gather

two balloons two plastic PET bottles (125 L softdrink bottles work well) a metal skewer large darning needle or a knife

WHAT TO DO1 Ask an adult to make a small hole (less than one centimetre across) in the bottom of one of the bottles Be

very careful when you do this because PET plastic is extremely strong 2 Stretch the neck of a balloon across the opening of each of the bottles Gently push the balloons so they

sit inside the bottles3 Try and blow the balloons up in the bottles Which one is the easiest to blow up4 Take the PET bottle with the hole in it and place your finger tightly over the hole What happens when

you try and blow it up now

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5 Take the PET bottle with the hole in it and blow the balloon up inside it At the end

of your last breath place your finger over the hole and take your lips off the bottle What happens to the balloon

6 Gradually release the pressure of your finger What happens to the balloon nowWHATS HAPPENINGYou probably found that you could blow up the balloon in the bottle with the hole in it You wouldnt have had much luck with the other one though Dont worry There is nothing wrong with your lungs Its got to do with spaceAir takes up space just like anything else When you blew up the balloons in the bottles you were trying to push air into a limited space There wasnt enough room for the air in the sealed bottle as well as the extra air you were trying to blow into the balloon And your lungs certainly dont have the power of an air compressor so you cant blow much extra air into the balloon in the hole-less bottleYou could blow up the balloon when the hole was uncovered because air escaped from the hole and made room for all the extra air you blew into it So you were blowing some air in the top but some was also escaping through the hole You saw the reverse happening when you blew up the balloon in the bottle with the hole and then put your finger over the hole As you released the pressure of your finger the elastic sides of the balloon forced the air out of the balloon returning it to its original size So air was forced out the top but was replaced by air entering back through the hole at the bottom

WHAT YOU NEEDTo do this experiment you will need

a balloon 25 cm of cotton thread a tap

WHAT TO DO1 Blow up the balloon and tie the end2 Tie the piece of thread to the end of the balloon3 Hang the balloon a few centimetres away from a stream of cold water rushing from a tap

WHATS HAPPENINGYou should see the balloon move towards the stream of water If you hold the balloon with your fingers instead of by the thread you may be able to make the stream of water move towards the balloon (as in the photo above)When you turned on the tap the rushing stream of water started moving the air around it Due to the fact that this air was moving it had a lower pressure than the surrounding still air Holding the balloon near the stream of water meant it had low pressure air on one side (the side near the water) and higher pressure air on the other side High pressure air always pushes towards low pressure air The higher pressure air on the other side of the balloon pushed the balloon towards the stream of water This is called the Bernoulli Principle

WHAT YOU NEEDTo do this experiment you will need to gather

a hard boiled egg (boiled for 15-20 minutes) that has been allowed to cool a glass bottle or jar with an opening at the top a couple of millimetres smaller than the egg some newspaper matches or a lighter

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a sink to do the activity on an adult helper

WHAT TO DO1 Peel the shell off the hard boiled egg2 Place the pointy end of the egg in the neck of the glass bottle or jar3 Scrunch up a piece of paper and light it then lift the egg up and carefully (but quickly) put the burning

paper into the bottle and replace the eggWHATS HAPPENINGThwump - the egg gets sucked into the bottleThe burning paper causes the air inside the bottle to expand pushing some of it out of the bottle When the paper goes out the air cools and contracts The air pressure outside the bottle is greater and the egg is pushed into the bottleTo get the egg back out of the bottle wash the ashes out of the bottle Turn it upside down and position the egg with the pointy end back in the opening Take a deep breath and blow in Continue to hold the bottle upside down wait and watch

WHAT YOU NEED

What will happen when you drop itTo do this experiment you will need

four pieces of plywood a balloon a lead sinker a needle rubber bands tape nails a hammer

WHAT TO DO1 Put together a rectangular wooden frame2 Using elastic bands suspend a lead sinker from the top of the inside of the frame so that the rubber bands

are stretched Attach an upward facing needle to the sinker3 Inflate a balloon and stick it to the top of the frame so the needle is suspended below the balloon

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4 Try dropping the frame from a couple of metres high with someone there to catch it so your construction

isnt damaged when it hits the ground What happens to the balloonWHATS HAPPENINGWhen an object falls the effects of gravity are cancelled out and an object experiences weightlessness In this case the frame and the objects inside become weightless However if the lead sinker becomes weightless the elastic bands which are stretched will now pull the sinker up causing the needle to puncture the balloon

EXPERIMENT 2 DROP CUPMany strange things happen with falling objects due to the effects of gravity being cancelled out Whats not happening in this experiment that you would expect to happen under normal circumstancesIts best to do this experiment outside as it will make a messWHAT YOU NEEDTo do this experiment you will need

a styrofoam cup a pen or pencil water

WHAT TO DO

What a difference a drop makes1 Fill a styrofoam cup with water and put a hole in the bottom side of the cup with a pencil As

youd expect water pours out (as in the cup on the left in the image)2 Now drop the cup full of water Its a good idea to have a bucket under the falling cup to prevent a mess

when it hits the groundWHATS HAPPENINGThe water becomes weightless while the cup is falling and for the duration of the fall it no longer pours out of the holeSee if you can come up with your own falling demonstrations that might produce other interesting effects

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WHAT YOU NEEDTo do this experiment you will need

a film canister baking soda (sodium bicarbonate) vinegar (any kind will work but white vinegar is easiest to clean up) an ice cream stick or teaspoon a plate saucer tray or similar eye protection (glasses sun glasses or safety goggles) an adult

WHAT TO DO1 Take the lid off the film canister Before adding the ingredients practise putting on the lid and placing it

upside down as described in step 52 Put on your eye protection3 Pour a small amount of vinegar about 5 millimetres deep into the body of the canister4 Using the teaspoon or icecream stick place enough baking soda to fill the recess in the lid5 Hold the body of the canister in one hand and the lid in the other Quickly and firmly press the lid

completely on place the canister lid down on the plate and stand back Make sure your plate is on a level surface Your canister rocket will blast off seconds later The exact timing will depend on the canister temperature amount of ingredients and how tightly you packed the baking soda in

6 Have a close look at the lid and bubbling ingredients left on the plateWHATS HAPPENINGWhen vinegar and baking soda mix together there is a fast chemical reaction There are several products of the reaction although it is the carbon dioxide gas (C02) that pops the lid offAs more and more carbon dioxide is produced the bits of carbon dioxide (called molecules) are squashed together and begin to push or apply a force on all the inside surfaces of the canister including the lidPressure is defined as a force over an area In this case its the force of the carbon dioxide pushing over the inside area of the canister As the carbon dioxide builds up so does the pressure inside the canister The pressure quickly pops the lid offA good way to understand what is happening is to take a deep breath in seal your lips and slowly breathe back out into your mouth Eventually your mouth cannot hold the pressure and your lips will unseal letting some air out Caution dont overdo this as you can hurt your eardrumsThe carbon dioxide gas pushes down on the lid although as it is sitting on the plate it cant go anywhere when it pops The carbon dioxide is also pushing on the inside base of the canister (the top of your rocket) and this pushes it into the air

To do this experiment you will need a balloon (not blown up) a short piece of drinking straw a long piece of string sticky tape two friends

WHAT TO DO1 Blow up the balloon and hold the neck to stop the air escaping

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Cartoon of the jet balloon experiment2 Ask your friends to hold either end of your string so the string is taut3 Thread the straw onto the string and tape it to the balloon so that one end of the straw points to the neck

of the balloon4 Hold the balloon at one end of the string and let go of it

WHATS HAPPENINGThe balloon should fly to the other end of the string as it deflatesMany years ago a scientist named Isaac Newton realised that when an object applies a force onto another object the other object pushes back with an equal force in the opposite directionWhen you let go of the balloon the air is pushed out of the neck of the balloon As it does the air pushes on the balloon with equal force in the opposite direction so the balloon is pushed along the string The air comes out of the balloon faster than the balloon is pushed along because the air is much lighter than the balloonAll rockets work by using the same principle In a rocket fuel is burned in a combustion chamber which is open at one end As the fuel burns it produces hot gases which rush out the open end of the chamber Since the gases are being pushed in one direction by the rocket the rocket is pushed in the opposite direction with equal force

WHAT YOU NEEDFor this experiment you will need

a small soft-drink bottle with its label removed (one with straight sides works best) a torch milk correction fluid (such as liquid paper) or paint a very dark room (try to do the experiment when it is dark outside) sink bucket or jar a thumbtack or safety pin sticky tape scissors paper

For this activity we will need to make a thin straight beam of light Most torches produce a fairly wide beam so you may need to use the paper to cover most of the end so only a thin beam of light comes out Try for a beam with a width of one centimetre or lessWHAT TO DOThere are two parts to this activity The first part shows how light bounces underwater

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The light beam is reflected back into the water1 Fill your bottle partway with water2 Add a drop of milk to make it easier to see the path of the light through the water3 Place the bottle near the edge of a table in your dark room4 Hold the torch down fairly low and shine it up through the side of the bottle onto the bottom of the

waters surface You should find the light travels up through the water through the surface and into the air

5 Keep the beam of light aimed at the same point on the surface but slowly lift the torch up so the angle between the light and the water becomes smaller and smaller

6 When the angle between the water and the beam of light becomes small enough the light will not go through the surface any more but will bounce off it like it was a mirror

The next part shows how to trap light in a stream of water1 With the thumbtack make a small hole in the bottle a couple of centimetres from the bottom You might

find this easier if the bottle is filled with water so the sides dont bend when you push on them2 Empty the bottle dry off the outside and paint around the hole with correction fluid or paint Paint at

least one centimetre in each direction and a couple of centimetres downwards This ensures that the beam of light only travels down the stream of water

3 Fill the bottle with water until the water squirts out the hole in a steady stream Make sure you have a sink or bucket set up to catch the water

4 Shine your torch at the hole from the other side of the bottle5 As the water comes out of the bottle it will look clear until it starts to break up into drops At that point

you may see some light glittering on the drops Hold your finger in the water stream above the point where it breaks up You should see a spot of light on your finger

6 If you look closely you should find that the point of light is actually below the level of the hole The light has stayed inside the stream of water as it bent down

WHATS HAPPENINGBoth of these activities rely on an effect called total internal reflection

The beam of light stays inside the stream of waterWhen light hits a boundary between two substances like the surface of water it often bends This is called refraction In the case of water and air light bends towards the surface of the water when it goes from water into air

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As the angle on the water side becomes smaller the angle on the air side gets smaller even faster When the angle on the water side is just right the angle on the air side would have to be zero so the light would be trying to go along the surfaceIf the angle on the water side is any smaller then instead of going through into the air the light bounces off the surface of the water This is called total internal reflection For the surface between water and air the critical angle is 415 degreesIn this activity the light stayed inside the stream of water because of total internal reflection To start with the light and the water both come out of the hole horizontally As the water

curves down the light eventually hits the surface Since the angle between the surface and the light is very slight the light bounces offAs the water keeps bending the light inside it keeps bouncing off the surface until the water starts to break upThe same effect happens inside other clear materials such as long thin strands of glass or plastic even if the strand curves or goes around in circles This is called an optic fibreAPPLICATIONSDoctors can look inside a persons body using a bundle of optic fibres connected to a television camera outside the body This has lead to keyhole surgery where doctors carry out complicated operations through small holes in the skin instead of having to make large incisionsOptic fibres are also used to carry information like telephone calls By sending the information as carefully controlled pulses of different coloured light it is possible for a single fibre less than a millimetre wide to carry thousands of phone callsOptic fibres are becoming more important as scientists and engineers are developing technology called photonics which is the study of ways to generate and harness light and other forms of radiant energy

WHAT TO DO1 Cut a circle from a piece of cardboard2 On one side draw a head with an apple on it3 On the other side of the cardboard draw an arrow (or pick two other related pictures like a fish and a

fishbowl)4 Use sticky tape to attach the circle onto a straw5 Roll the straw back and forth between the palms of your hands while you look at the cardboard What do

you seeWHATS HAPPENINGModern movies use technology to produce an optical illusion and fool our brainsWhen you look at a picture your eye and brain retain the image for a fraction of a second after it has gone This is called persistence of visionIf you are shown more than ten pictures a second your brain will merge the separate images into a series of moving imagesMotion pictures show 24 still frames per second that give the illusion of smooth motion The brightness of an image also affects the length of time the image will remain in your brain

WHAT YOU NEEDTo do this activity you will need

sunlight a piece of card with a one millimetre wide slit cut into the middle a straight-sided glass filled with water

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