Science experiments at home

Try to work out why things happen first, then compare your ideas with the explanations and comments provided as links.

This is a sampler page that makes a good place to start: you can just browse around, using the idex on the left, or you can go off first and find out about the rest of this very large site -- there are lots of other pages, with even more stuff to play around with, and even project ideas for science fairs.

Activities

Balloon
Bernoulli effect
Block and tackle
Boiling water?
Bubbles
Cartesian diver
Centre of gravity 1
Centre of gravity 2
Coiled snake
Coin drop
Comeback tin
Compaction
Contraction
Convection
Coupled pendula
Custard powder
Density
Dropping coins
Egg in a bottle
Flotation
Goo
Gyroscopic effect
Hovercraft
Ice melting under pressure
Inertia bricks demonstration
Leaf structure
Light bends
Lissajous figures
Machine
Materials and their properties
Möbius strips
Move the cups
Natural dyes
Optical illusion
Osmosis
Oxidation
Pascal's Principle
Persistence of vision
Pile driver
Pressure 1
Pressure 2
Pressure 3
Pressure 4
Pressure 5
Pressure 6
Pulley
Racing jars
Refraction
Resonant pendula
Rolling jars
Soaking some spuds
Soda water
Steel heat
Strange balance
Strange matter
Strong arches
Suction 1
Suction 2
Suction 3
Topology
Torsion pendulum
Toy tank
Treading on eggshells
Turbine effect
Windvane
Other pages on this site

How to do it


Wind vanes
This diagram shows you how to make a wind vane. Use a piece of cardboard from a manilla folder, and sticky-tape a washer (or a coin) to the front end. Then find the balance point by sticking a pin in until you get it right, and tie on a piece of cotton.
When you hang this, it will point to the direction the wind is coming from, but if you walk around with it in front of you, it will always point in the direction you are going.

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A toy "tank"
You will need a wooden cotton reel, a small wood saw, a large rubber band about 100-120 mm in circumference, a stick or pencil about 10-15 cm long, a small (shorter than reel diameter) nail, and a slice from the base of a candle with a hole in the centre.

What you do:
This is an old traditional children's toy that still fascinates. Use a tenon saw or similar to cut a V-shaped groove across the centre of one end of the reel, then thread the rubber band through the hole in the reel. Slip the nail through the rubber band and settle it into the slot. Slip the candle slice over the rubber band at the other end, and put the stick through the rubber band. Wind the stick around until the rubber band is quite tight, then put the cotton reel down and watch it run.

This will help you understand


comeback.gif - 3301 Bytes The comeback tin
Another old favourite. This one calls for a coffee tin, a drill, a length of elastic, cotton thread or string, and a small weight. Drill two holes in the lid of the tin, about 50 mm apart, and two matching holes in the base of the tin. Thread the elastic through the base holes, and also through the holes in the lid, and tie the ends. Then tie the two sides of the elastic together with the string, and use the string to tie the weight tightly to the elastic.

Take the two ends of the elastic up through the lid holes, put the lid on the tin, and tie off the two ends. Roll the tin away from you: this should "wind up" the elastic, causing the can to roll back again. This can be quite mystifying to those seeing it for the first time.

This will help you understand


Inertia bricks
What you need:
You will need a strong stand (or a timber beam between two tables or chairs), several bricks, strong cotton thread (some testing will be needed).

What you do:
Hang one brick by the cotton, and then hang a second piece of cotton from the first brick. Tie on a second brick and let it drop (WATCH YOUR TOES!). The thread breaks between the two bricks. Now repeat, but dangle the second brick gently: with the right strength cotton, you will now get a break above the first brick. The inertia of the first brick protected the top cotton in the first case, but not in the second case. If this does not work, dangle two bricks and drop a third: keep escalating until you get a result!

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Resonant pendula
You will need:
Two supports that will hold up a horizontal slack string, several lengths of string, and some small masses.
What you do:
Dangle two of the masses from the slack string by lengths of string, making sure that the strings are the same lengths. Set one pendulum swinging, and watch what happens after a few minutes. Now add another mass on another string, and experiment: is there a transfer of movement when the lengths are different? When the masses are different? When there are several hanging on the one system?

This will help you understand


Coupled pendula
What you need:
Very fine wire spring, two identical heavy pendula on stands

What you do:
Hang the two pendula on their separate stands, and join them, near the bottom, by a very fine, loosely coiled spiral of wire. Set one swinging, and watch what happens.

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Lissajous figures
To Australians, the Lissajous figure (or one of them, at least) is familiar as the logo of the ABC. Lissajous figures arise when two simple harmonic motions interact at right angles to each other, so long as the periods of the two motions are in a simple mathematical relationship, such as 3:2.

This is the simplest way to generate these figures, just by having a cup which dribbles sand, suspended as shown in the diagram.

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Torsion pendulum
What you need:
Some piano wire, two tables, a length of 4" x 3" or 3" x 2" timber (that is, 100 x 75 mm or 75 x 50 mm), about two metres long, a metre length of 2" x 1" (41 x19 mm) dressed timber, drill and drill bit, pliers or wire cutters, and a couple of weights. Piano wire might be hard to get: hardware stores sometimes sell it. You will be able to make do with fencing wire or baling wire, so long as the pendulum does not swing too far from side to side. You may want a couple of clamps to hold the whole rig on the tables: if you do, be sure to use scrap timber to protect the tables from the jaws of the clamps, or somebody will get angry !

What you do:
Drill two holes close together through the larger piece of timber, and cut off about 800 mm of the wire. Push some of the wire through one hole, bend a right angle in it, and then another, so that you can ram the short end down into the second hole (the main thing is to have the wire attached in such a way that it is unable to rotate.) Then attach the 2x1 timber to the other end of the wire, with the long end of the wire going carefully through a centre hole, and up through a second hole, to one side. Now sling the support beam between two tables, add some weights, twist the smaller piece of timber sideways, and let go.

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Natural dyes
A word of warning: aluminium saucepans and pots have a very thin layer of aluminium oxide which will bond tightly to some of these organic dyes. Use an old pot, or one that does not matter!

Many natural dyes can be made from things you buy at the greengrocer's shop or the florist's. Beetroot, onion skin, carrot, rhubarb, spinach, many colourful flowers and berries, tea and coffee are just some of the things you can use. Many kinds of tree bark are also useful for brown dyes.

You need to chop or grind whatever you are trying, bring to the boil and simmer for half an hour or so, adding more water as some evaporates off, then dip in a test square of cloth and leave it for fifteen minutes, then hang it out to dry.

The uptake of dyes can be improved with a mordant. Add half a teaspoon of ordinary alum to about 500 mL (just under a pint) of water in a plastic container, and dissolve it. Then make up 500 mL of diluted household ammonia, and add it to the alum solution: this will produce a gel of aluminium hydroxide, which clings to both the fibres and the dye.

This will help you experiment further


Time heals all wounds
Find a small-necked, corked glass bottle and balance an ice cube on top of the cork. Cut a 40 cm piece of thin, strong wire and tie a hammer to each end. Balance the wire across the middle of the ice cube. What do you think will happen? Try it!

You may like to stop and wonder why you need to use a glass bottle and a cork (there is a reason!!).

You may also like to note that the "standard" explanation for this demonstration is probably wrong!

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Gyro
Tie one end of a long piece of string to the middle of a matchstick. Pull the other end of the string up through the hole in the centre of an old-fashioned vinyl record (so the matchstick is centred underneath the hole). Try to swing the record backwards and forwards like a pendulum in smooth, even movements. Now give the record a spin. What will happen when you try to swing the record again? Test your hunch.

Does this remind you of riding a bicycle? (It should!)

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Hero was here!
Poke a hole in the bottom left hand corner of each of the four faces of a large paper milk carton. Poke an extra hole in the top flap of the carton and tie a string through it. Hang the carton from the string. Cover the holes with your fingers and pour water into the carton. What will happen when you remove your fingers from the holes?

Find out who Hero of Alexandria was! Work out what this question has to do with a spinning milk carton.

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Treading on eggshells
Carefully break off the small end of four eggs and pour out the insides. Wind a piece of sticky tape around the centre of each eggshell. Cut through the centre of the tape to make four dome-shaped shells (discard the broken end of each shell). Lay the four domes on a table with the cut sides down arranged in the shape of a rectangle. Next, guess how many telephone books you can lay on top of the shells before they break. Try it!

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Soak Some Spuds
Slice a small potato lengthwise into several pieces that each have two flat sides. Place some of the pieces in one dish and the rest in another. Fill both dishes with water. Add two tablespoons of salt to one of the dishes, and label it "salt water." Let the potatoes soak for 15 minutes.

Compare the potatoes. Is there a difference in firmness? Why?

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Mobius strips
Cut a 5-cm strip lengthwise from an old newspaper. Holding the strip out straight, give it a half twist (180 degrees) and glue the two ends together. Take a pen and carefully draw a line along the centre of the strip. Where do you end up? Is the line drawn on the inside or outside of the paper? Now cut the strip along the line you drew. How many chains do you get? Now try cutting a half-twist strip, one-third of the way from one edge.
There are some more mathematical things to be found here

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Getting the bird in the cage
Draw a picture of your favorite bird on a small index card. On another card the same size, draw a cage. Now tape the two cards, drawing sides out, on opposite sides of a pen. Spin the pen between your hands or fingers. Is your bird still free or did you catch it and put it in the cage?

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Strange matter
Mix one and one half cups of cornflour with one cup of water in a bowl. Slowly dip your finger into the gooey mixture; then try slapping it hard with your hand or a heavy spoon. What happens? Why?
Then try letting some of the goo flow across a piece of rubber sheet cut from a rubber glove. Stretch the rubber slowly, then stretch it fast, and notice what happens each time.

Get a pair of scissors, and pour some of the mix from a spoon. Can you snip the stream with the scissors? (Think: would I ask you this if you couldn't do it, somehow?)

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Density stacker
How? Pour one-third cup of golden syrup (cocky's joy, molasses or treacle) into a glass jar followed by one-third cup of cooking oil. Then pour in one-third cup of water. Drop in a piece of plastic, followed by a grape, followed by a small cork. What happens? Why?

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Fire extinguisher
Place a short candle, a slightly taller candle, and a small dish or small glass filled with baking soda in the bottom of a large bowl. Both candles should be below the top of the bowl. Light both candles. Then pour vinegar into the dish of baking soda. Observe the foaming reaction. What happens to the candles? Why? In what order?

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Dancing raisins
Fill a glass or bottle half full with soda water. Drop three or four raisins into the water. Wait. What happens? Why?

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Cartesian diver
Fill a plastic bottle almost to the top with water. Attach a small piece of clay on the clip of a plastic pen cap. Place the cap in the bottle so it floats and seal the bottle tightly. Squeeze the sides of the bottle. What happens? Why?

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No Sucker
Fill a small jar with water. Poke a hole in the lid big enough for a straw. Put a straw into the water through the hole in the lid and seal up the space around the straw with Plasticine. Now try to suck water through the straw. Be sure there are no leaks. What happens? (Or doesn't happen?)

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What's in a leaf?
Fill a bottle with water to within about 2 cm from the top. Take a freshly cut leaf, wrap clay or Plasticine around the stem and place the stem into the bottle. Make sure the clay fits snugly around the mouth of the bottle. Poke a hole through the clay, and insert a straw. Press the clay around the straw and bottle opening so that no air can escape. The straw should not touch the water. Stand in front of a mirror and suck the air out of the bottle with the straw. (This is hard to do if there are any leaks.) What do you observe in the mirror?
There are some more enquiries about living things to be found here

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Hovercraft
You will need a balloon, a cotton reel (or better still, a cork), a cork borer, some glue, a small sheet of hardboard (or laminate or similar, but NOT cardboard), a saw, and a drill. Carefully cut a disc from the hardboard and drill a small hole through the centre. Bore a larger hole through the centre of the cork and glue it, wide-side-down to the centre of the piece of board, gluing it to the less smooth surface. When the glue is set, blow up the balloon, fit to the cork, and place the whole lot on a smooth table, or a larger piece of laminate. The balloon has a limited life span as an air source, but it does not make the model spin as an electric motor would.

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Getting an egg into a bottle
Drop three lit matches into a glass bottle that has a narrow neck (an old-style 600 mL milk bottle works well). Quickly put a peeled, hard-boiled egg on the mouth of the bottle. What happens? Why?

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Can you score a goal?
Take an empty, 2-litre soft drink bottle and lay it on its side. Ball up a small piece of paper so that it will fit through the mouth of the bottle. Hold a hair dryer so it blows directly on the mouth of the bottle. Try to push the paper into the bottle using the air stream from the hair dryer. What do you think will happen to the paper?

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Out of sight
Place a coin on a white piece of paper. Put a clear glass filled with water on top of the coin. Can you see the coin? Where is the best place to see it? Now place a saucer on top of the water glass. Try to find the coin without looking straight down through the water glass. Can you do it?
There are some more enquiries about sight and light to be found here

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Racing jars
Take two identical clear-glass jars, leave one empty, and fill one with water. Put the lids on both jars and tighten. Place a large, three-ring binder on a level floor, and start the jars from the top of the "ramp" the binder forms. Release them and watch what happens. Which one gets to the bottom of the ramp first? Which one rolls the farthest?

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Which coin drops fastest?
Put a coin at the edge of a table. Put the edge of a ruler behind the coin, with the rest of the ruler extending out over the table edge at an angle. Put another coin on the end of the ruler that extends beyond the table edge. Take a second ruler and hit the first ruler (on the edge sticking out beyond the table edge) so that the first coin is thrown off the edge of the table and the second coin drops off the ruler. You have to listen for the results so you want to do this over a hard floor. Listen carefully: Which coin hits the ground first?

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Convection snake
Cut a piece of paper into a 6 cm diameter spiral (use the diagram). Cut a piece of thread 15 cm long and tape one end of the piece of thread to the centre of the paper spiral. Position a desk lamp so that the light points upward. Ask an adult to hold the paper spiral by the thread about 10 cm above the light. (Caution: Do not allow the paper to touch the light bulb.) What happens?

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Steel heat
Put a sensitive thermometer in a jar and close the lid. Wait five minutes and record the temperature. Remove the thermometer from the bottle. Soak half of a steel wool pad in vinegar for one minute. Squeeze excess vinegar out of the steel wool pad and wrap it around the bulb of the thermometer. Place the thermometer and the steel wool into the jar and close the lid. Wait five minutes. Record the temperature. What happened to the temperature?

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Move the cups
Find two disposable cups and some string. Cut the string into two 30 cm pieces. Using tape, attach the end of one piece of string to the bottom of one of the cups, and attach the other end to the edge of a table. Repeat this with the other cup. Position the cups so they hang off the table 4 or 5 cm apart, and at the same height. You might need to adjust the spacing between the cups. Blow between the two cups and see what happens?

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Negative inflation
Fill a plastic (PET) bottle with hot water (NOT boiling water -- see if you can work out why I said that!) and fill a bowl with cold water. Let them sit for one minute, then empty the bottle quickly. Stretch a balloon over the open end of the bottle and push the bottle down into the cold water. What happens? Why?

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Cold boiling water?
Fill a glass three-quarters full with water. Place a handkerchief over the top of the glass and hold it on with a rubber band placed around the rim of the glass. Push down on the centre of the handkerchief until it touches the water (the experiment works best if the handkerchief is slightly wet). Keep your fingers pressed on the handkerchief and turn the glass upside down.
The water will stay in the glass. Now, pull the handkerchief tight, so that the concave shape disappears. What happens? Why? Is it really "boiling"?

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Pile driver
Fill a plastic jar with rice, carefully jab a knife into the rice five or ten times. The rice will settle a bit, then add more rice. Continue until no more rice can be added. Then quickly jab the knife into the rice and lift. What happens? Why?

Can you work out why this item is called "Pile driver"?

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Strange balance
Tie a string in a loop and slip it over a ruler. The other end should twist into a loop and slide over the handle of a hammer resting at the end of its rubber grip. Place the ruler's edge with the hammer head underneath on the edge of a table. The hammer handle should rest against the other end of the ruler. What happens? Why?

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A block off the old chip
A "block" is what sailors call a pulley, or a set of pulleys. You can use simple blocks of wood like this with screw eyes and screw hooks to make simple weight-lifting systems. You can screw them into the wood by hand, if you make a small starter hole with a gimlet, a nail or best of all, a drill.
The idea is to fit a thread to link two of the blocks, as you can see in the picture on the right. Try making two blocks like this, set them up, and then test them to see how many standard masses you can lift with a single standard mass. There is more friction here than in a block and tackle with pulleys, of course.

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And now for some help

The tank
Stored energy, friction and the reduction of it with the candle, and also if the cotton reel needs to be roughened up to make it grip the "ground".

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Why the comeback tin comes back
The rolling tin stores energy in the elastic, because the weight always hangs down as the tin rolls in one direction. This works best on the sort of coffee tin that has a metal lid that clips into the top of the can. Try making a second one in a clear plastic container, to see how it works.

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The inertia bricks
A thick pile of newspapers in a box on the floor will make this a whole lot quieter and safer!!
The idea of inertia is also behind the trick where you take a potato and soak it in water (to make it nice and crisp), then you can spear a drinking straw into it, because of the inertia of the potato.

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Resonant pendula
The principle of resonance causes the energy to be transferred from one pendulum to the other, and then back again, provided they are the same length. I have never tried this, but a pendulum should also influence one a quarter of its length (i.e., with half the period), but there should not be the chance to "return the compliment". This is a simple toy which can give you hours of pleasure.

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Coupled pendula
Because the two pendula have the same length, this means they have the same frequency. So when the swinging pendulum pulls gently on the other pendulum each swing, it does so at just the right speed to keep transferring energy across.
Think of the timing you ahve to use when you are pushing a child on a swing.

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Torsion pendulum

The torsion pendulum has a constant period, regardless of the displacement: try varying the weights, or their placement, and see what the period (one full cycle from stop, through turn through stop through turn back through to stop again) is. You can also try heavier beams on the bottom.

References:
There are only a few of them, but Coulomb developed the theory so he could carry out other experiments, somewhere back around 1820. John Michell used the torsion pendulum to plan an experiment that would weigh the earth -- in the end, the experiment was done by Henry Cavendish. The idea, as Coulomb explained it, is that a very thin wire, which delvers a very weak restoring force, will allow even small forces to be measured. And the beautiful part is that you can use simple mathematics to calculate the restoring force associated with a deflection of just a few degrees!

In the late 1990s, a torsion pendulum was used to prove the existence of something called the Casimir effect. You will have to hunt this one up for yourself.

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Lissajous figures
I haven't got round to this one yet. Look it up, write a good explanation, and i will put it here with your name on it :-)

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Dyes
There is a great deal of room for experimentation: lichens can be used for colours, blenders can be used to do the grinding and chopping, and it may be that you can do some useful work with a microwave. Try fern stems and fern roots, and experiment with small amounts of vinegar or lemon juice (acid) or dilute ammonia (alkali) to change the colours, as most dyes work as "indicators".

Oak bark is a traditional European and American source, but what about the acorns, or the barks of gums and wattles, or other trees that grow where you live? Many wattles were used in the past as a source of "tanbark", bark from which tannins could be extracted to be used in tanning leather.

You might also like to investigate other mordants, and try the dyes on different types of cloth: what works on wool may not work on cotton, and vice versa.

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The cutting wire
Standard explanation:
The pressure of the wire causes the ice to melt beneath it. The wire sinks easily through the melted ice, while the ice above the wire, which is no longer under pressure, refreezes. This scientific principle also applies to ice skating. The pressure that your skates exert on ice causes a layer of water to form under the blades, creating a slick and slippery surface for sliding. (But see "Reality" below.)

The glass of the bottle and the cork are both insulators, so they stop the ice block from melting too fast. The wire, on the other hand, is able to conduct heat (warmth) from the outside. By the way, you need to do this on a cold day: if the temperature is more than about 10 degrees C, the ice block will melt too fast, and it will probably not freeze again! But on days like that, you can probably still get a result with a larger ice block, and a piece of wire with 5 kg weights on either side.

Research problem: would there be a temperature below which you would not see this effect at all? How would you find out if you are right?

Reality:
The change in melting point due to the pressure is so small that the main melting effect in this demonstration comes from heat conducted into the ice along the metal wire. To test this claim, you would need to replace the wire with string or cotton, and maybe try to see what happens at temperatures close to freezing, when the pressure effect will not be changed, but conduction will be reduced to a minimum.

So if the pressure thing doesn't happen that way, why do the skates work? Well, contrary to what most books say, scientists now believe that there is always a thin fluid layer on the surface of ice, so you don't need the "pressure effect". Here is a link to more information on this.

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Hero's carton
Newton's Third Law states that every action has an equal and opposite reaction. Water shoots out the holes, and pushes back on the carton with equal force. A turbine is formed as the energy of the moving liquid is converted into rotational energy. This principle was known to Hero of Alexandria (also known to us as Heron of Alexandria).

You can also do this experiment with an aluminium drink can. Make holes near the bottom in about four places with a nail, and in each case, lay the nail over, so the hole will squirt sideways. Cut the top off the can carefully with scissors and hang the can, using fishing line and a fishing swivel, under a flow of water.

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The swinging record
The simple answer is that the record has something called gyroscopic inertia, the same thing that stops a toy top from falling over while it spins.
To a scientist, gyroscopic inertia is the property of a rotating object to resist any force which would change its axis of rotation. Once the record is set spinning at an angle perpendicular to the string, it will resist any forces (such as gravity) that try to change that angle.
By the way, I have tried doing this with several Barry Manilow records, and they just don't swing at all.

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The supportive eggshells
Arches — even those made of eggshells — are strong because they exert horizontal as well as vertical forces to resist the pressure of heavy loads. The crown of an eggshell can support heavy books because the weight is distributed evenly along the structure of the egg.

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Why the potato went floppy
Through osmosis, water moves from areas of low salt concentrations to areas of high salt concentrations. Adding salt to the water creates a higher salt concentration in the dish than in the potato. Consequently, water in a potato that is soaking in salt water migrates out, leaving behind a limp spud!
People often make celery and strips of carrot go crisp by soaking them in fresh water. What happens if you soak these vegetables in salt water?
There are more experiments with living things at this link. There is also an experiment on diffusion which will help you understand osmosis a bit better.

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One side of the Möbius strip
Your piece of paper is called a Mobius strip, which is a shape described by a branch of mathematics called topology. When you twisted your strip, the inside and outside became one continuous surface. And when you cut the strip, it became one longer chain but still had only one continuous surface.
Try the experiment again and give the paper a full twist. Then try one and a half twists, and see what happens.
See what you can discover about Klein bottles.

Back to the question. Or you can look at some more number things.

Why does the bird appear to be in the cage?
It appears to be caged because of how your eyes and brain work. When you see the image of the bird, your brain holds onto the image for a short time--even though the image appears and disappears quickly. The same thing happens with the image of the cage. The two images actually overlap in your brain so the bird appears to be in the cage.
The technical name for this effect is persistence. It is what lies behind every movie and every TV program that you see.

Back to the question Here is a link to sight and light , where these ideas are explored further.

Why does the starch do this?
The molecules in the starch are very large compared with molecules of water or other ordinary molecules. When you slap the surface quickly, the get tangled in each other, and this stops them splattering. In this way the mixture behaves more like a solid. If you move them slowly, or let them flow, they can run past each other, and so the starch behaves like a liquid.
You can also use custard powder for this experiment, but watch out, because the custard leaves yellow stains if you spill it on anything. (Custard powder is mainly corn starch.)
Check to see if this yellow colour is an indicator for acids and alkalis.

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What puts out the candles?
When vinegar reacts with baking soda, carbon dioxide gas is produced. This gas is heavier than air so it sinks to the bottom of the bowl and slowly begins to fill up the bowl as though it were water. When the level of carbon dioxide has risen to the level of the flame, the flame will go out from lack of air.

Did you notice which candle went out first? Does this suggest anything about how the gas filled the bowl?

When you burn a candle, carbon dioxide is produced, yet this carbon dioxide does not put the candle out. Can you suggest why that might be?

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Why do the different liquids stack in layers?
The liquids have different densities. The most dense (golden syrup) will be at the bottom, the least dense (oil) will be at the top, with the water in between. Each object will sink to the level of the liquid that has a greater density than the object. The object will then float on that layer.

The water and golden syrup will mix, which is why you add the oil first, so the water just drifts down and sits on top of the syrup. The syrup will slowly diffuse into the water over time, and vice versa.

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Why do the raisins bob to the surface?
Soda water contains dissolved carbon dioxide gas that collects on the irregular surfaces on the raisins. Once enough bubbles have collected, it will actually lift the raisins to the surface where the gas is released into the air, causing the raisins to sink once again.
There are more experiments with bubbles

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Why does the pen cap sink?
By squeezing the bottle, you increase the pressure inside, thus forcing more water up into the pen cap. The added water in the cap increases its weight and causes the cap to sink.

You can make this sort of diver in other forms. A partly water-filled eye-dropper will work, and so will a drinking straw, blocked at the top with color and weighted around the outside of the bottom with a larger piece of Plasticine

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Why does the egg go into the bottle?
The flames heat the air in the bottle. As the heated air expands, some of it escapes out the bottle. When the matches go out, the air inside the bottle cools and contracts, thus creating a lower pressure inside the bottle than outside. The greater pressure outside the bottle forces the egg into the bottle.

Break up the egg with a skewer to get it out of the bottle again, unless you can think of a safe way to make it pop out in one piece, remembering that thick glass sometimes shatters if it comes in contact with very hot water.

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Why won't the paper go into the bottle?
In trying to push the paper into the bottle, you are aiming the air stream at the mouth of the soda bottle. The hair dryer pushes air into the bottle, filling it with slightly compressed air. In fact, the bottle is so full of air that there is no room for anything else to enter -- not even a little ball of paper. If you turn off the hair dryer or aim it away, the air can escape the bottle and there is room for the paper.

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How did the coin disappear?
We see objects because light rays reflect off them and into our eyes. But light bends each time it hits a substance of a different density. The light reflecting off the coin must pass through air, glass, and water (all with different densities) to get to your eye but the light bends so many times that by the time it gets to your eye, it looks like it's somewhere that it's not!

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Why did the empty jar win?
At first, the water-filled jar moves down the ramp faster than the empty one. This happens because its weight is evenly distributed throughout its volume, thanks to the water inside it. The empty jar's weight is all in the glass outside so it doesn't roll quite as fast. But as the jars begin rolling on the flat surface, the greater weight of the full jar causes friction between the jar and the floor as well as friction between the water and the inside of the jar. The full jar slows down, allowing the lighter, empty jar to take the lead!

A half-full tin of golden syrup will roll down the same slope in a most surprising way. Make sure the lid is firmly on, and make sure the tin is only half-full, or less.

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Why couldn't I get any water from the jar?
When you drink from an open glass of water, air pressure allows the water to travel up the straw. When you reduce the pressure inside your mouth (by sucking on the straw), the surrounding air pressure pushes down on the water and forces the liquid up the straw. But when air pressure on the water is blocked (when you seal the jar lid), there is no air pressure to help push the water up your straw. The air can't get to the water to push on it, so it doesn't go up the straw. Regardless of how hard you suck, the water stays where it is!

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Why did the coins land at the same time?
The coins start from the same height off the ground and are the same mass and shape, so gravity and air resistance worked on them in exactly the same way. Even if an object is thrown straight out, it will fall to the ground in exactly the same amount of time as an identical object that is dropped - the acceleration toward the ground that the objects experience as a result of gravity causes them to hit at the same time.

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Why does air appear at the end of the stem?
There are holes in the leaf called stomates and tiny tubes called xylem which run down the stem. The leaf and stem act as a straw for the plant. As you drew air out of the plant, more air was drawn into the bottle through the stomates and xylem. This is the same system that plants use to move water around.
There are more experiments with living things here.

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How does the hovercraft work?
The air flowing from the balloon through the hole forms a layer of air between the hovercraft and the table. This reduces the friction. With less friction, your hovercraft scoots across the table. As a rule, this model works best when you use a thin sheet of laminated material like Formica or Laminex, because the "card" needs to be very flat and quite stiff, although most books listing this experiment say to use carboard. The cork is lighter than a cotton reel, which makes it better.

There could be a good science fair project here for anybody who could work out how to mount a fan-driven blower on this "craft".

Probe

Give yourself a lift! An old-fashioned vacuum cleaner, where you can attach the hose to the "blow" end, can be used to make a hovercraft that will lift a person. You will need a piece of hardboard about 60 cm square, some heavy-duty plastic sheet, a hole saw, the right sort of vacuum cleaner, and some sticky tape.

Drill a hole in the centre of the hardboard to take the vacuum cleaner nozzle. Attach a "skirt" of plastic sheeting, about 10 cm wide, all around the edge of the board: this is used to contain the pressure below the board, allowing the craft to rise higher. Fit the vacuum cleaner and switch on. Fiddle for better results. This size lifted me when I weighed about 60 kg!

For better results, shape the skirt and attach it to the underside, so that it can not blow out on one side, spilling the air pressure. I used masking tape to hold it in place, but there must be better ways: research how they do it on a real hovercraft.

Another thought: try using a cooler fan from a computer, but get some advice about the correct voltage to use (and find out if they use AC or DC), think about why helicopters have a tail rotor, and then think about using four fans.

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Why does the paper spiral twirl?
The energy from the light heats the air above it. Warm air is lighter than cool air, so as the air heats up, it rises above the lamp. Cool air moves in to replace the warmer, lighter air. This "convection current" causes the spiral to twirl.

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Why did the temperature rise?
The vinegar removes any protective coating from the steel wool, allowing the iron in the steel to rust. Rusting is a slow combination of iron with oxygen. When this happens, heat energy is released. The heat released by the rusting of the iron causes the mercury in the thermometer to expand and rise.

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Why do the cups move?
Bernoulli's principle states that in areas where air moves rapidly, pressure is low. Blowing between the cups drops the pressure so the higher air pressure of the surrounding air pushes the cups together.

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Why does the balloon inflate into the bottle?
The warm water heats the bottle which, in turn, heats the air inside the bottle after the water is poured out. When the bottle is placed in the cold water, the air inside cools and contracts, causing outside air to be drawn in, pulling the balloon in and inflating it inside the bottle.

Try sitting the bottle back in the hot water again.

Another way to try this uses a balloon, a plastic drink bottle, some plastic tubing, rubber glue, a bicycle pump with the valve of the piston reversed (to suck instead of blow), and a drill.

You will have to drill a hole in the side of the bottle near the bottom, choosing a size which will just take the plastic tubing, and then glue the tubing in place. Hook this up to the pump, or use the connector from an old inner tube, but with the valve removed. Then push the balloon down through the neck of the bottle, and reverse the neck of the balloon down over the outside of the bottle neck. When air is drawn from the bottle, atmospheric pressure is greater, and the balloon "blows up" inside the bottle.

The main problem will be finding a bicycle pump which allows the valve to be reversed. The modern plastic variety does not allow this, so look for and old relic, with a metal barrel which can be unscrewed.

Yet another variation: Try shaking a small amount of very hot water in a bottle to heat the air inside, then quickly fit a balloon to the neck. Then wait a few minutes for things to cool down before you sit the bottle in an ice bath. Some of the pressure inside the bottle will have been a result of water vapour, which now condenses.

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Why does the hammer balance?
All objects have a centre of gravity that acts as if all the weight of the object were balanced there. The centre of gravity of the ruler is in the middle, but the hammer moves the centre of gravity of the system to under the table's edge which keeps it from falling.

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Why are you able to pick up the jar of rice?
The rice gets more and more packed down by repeated stabs from the knife until the rice is so compact that it presses against the blade of the knife with enough force to overcome the pull of gravity on the jar.

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Why does the water appear to boil?
Surface tension prevents the water from seeping through the handkerchief. When you straighten out the handkerchief, the water drops down to a new level, reducing the pressure in the air space at the "bottom" of the glass. The higher air pressure outside the glass forces air to penetrate the handkerchief and bubble through the water. But it's not really boiling!

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Why does the wind vane point at the wind?
The balance point for weight is at the front of the arrow, because of the washer (or coin) taped to the front. The balance point of the arrow's area for the wind to push against is further back, so the tail will always swing away from the wind, and the arrow will head into the wind.

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How can a block and tackle lift so much?

The block and tackle goes very slowly. With this arrangement, if you pull the outside line down one metre, the mass you are lifting will only go up 25 centimetres, because there are four strings supporting the lower block, and each one shortens by 25 cm. We can lift about four times as much weight as we are pulling with, but only about four times as much: we also have to lift the lower block, and there is some friction to overcome as well, and that means we have to pull a bit harder.

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This file is http://www.ozemail.com.au/~macinnis/scifun/miniexp.htm, first created on August 14, 1997, when it was planned to show some teachers how to set up this sort of simple page. Last recordedrevision (well I get lazy and forget sometimes!) was on October 21, 2001.

Worried about copyright? Don't be -- you need to go look at my fine print. Well, maybe you don't after you read the next paragraph, but do it anyhow . . .



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