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Impress your Mum and Dad! Amaze your friends! Eleven great science experiments you and your family can enjoy this weekend. Here Cambridge University scientists Chris Smith and Dave Ansell have devised some amazing DIY experiments for their website that anyone can do at home
Here, Victoria Moore gives you a step-by-step guide to some of the best - and explains how they work.
LEVITATE PING-PONG BALLS
You will need: a table-tennis ball and a hairdryer with a nozzle roughly the same size as the ball or a bendy straw
Point the hairdryer vertically upwards and switch it on. Then hold the ping-pong ball a few inches above the hairdryer nozzle - and let go.
You'll find that the ball wobbles around but doesn't fall to the floor. Even if you tilt the hairdryer so that the air stream is blowing at an angle, the ball remains aloft. You can even do it by blowing through a bendy straw . . . if you've got enough puff!
What you're witnessing is the Coanda effect. When a stream of air hits a curved surface, it's deflected from its original course and curls around it, hugging the line of the curve.
So, if the ping-pong ball bobs to the left, the air follows it and the pressure pushes the ball back to its original position - ultimately acting like an invisible hammock.
This principle, discovered by the Romanian inventor Henri Coanda, has been useful in aircraft design.
Slime ELECTRIC SLIME
You will need: cornflour, vegetable oil, mug, spoon, a balloon or some polystyrene
Mix a few tablespoons of cornflour with vegetable oil in a mug, aiming for the consistency of thick cream. Rub the balloon or polystyrene vigorously on your hair so that it gets charged with static electricity.
Pour some of the slimy cornflower mixture on to the spoon and move the spoon towards the 'charged' balloon. Keep your eyes on the slime, which will begin to behave like something from Dr Who, thickening and creeping towards the balloon.
What's going on? By rubbing the balloon on your head, you've transferred some electrons from your hair to the balloon, giving it a small negative charge.
Remember that old rubric - like charges repel and unlike charges attract? What's happening here is that the electrons - the negative parts of each of the tiny starch particles - within the slime are moving as far away as they can from the negatively- charged balloon. Each tiny bit of starch, instead of appearing neutral, now has a positive and a negative 'end'.
This has two consequences. First, the positive 'ends' of all the starch particles are attracted to the negative balloon - which is why the slime begins to twitch towards it.
And second, the starch particles become more attracted to each other, and therefore move together.
As the positive ends snuggle towards the negative ends, they create a thicker-seeming liquid.
TURN BREAD INTO SUGAR
You will need: one slice of cheap white bread
Take a bite and start to chew. When the bread turns to mush, don't swallow - just keep chewing. After a while, you should notice that the bread is beginning to taste sweet. Why? Well, bread is made from flour, which contains starch. Starch molecules are polysaccharides - which means that they consist of lots of sugar molecules joined together in a long chain. But our bodies can't absorb food in this form.
So, when we eat starchy substances - such as cake, pasta or potatoes - we use enzymes to break them down. An enzyme called amylase, found in your saliva, works on the bread starch as you chew. If you chew for long enough, the amylase will reduce the starch to sugar molecules, each containing six carbon atoms - in other words, glucose.
FREEZE A DRINK WITH INSTANT ICE
You will need: one unopened bottle of fizzy drink, a few ice cubes, salt
Crush the ice and layer it with salt. This makes an instant mini-freezer, capable of reducing temperatures to minus 18c.
Put the bottle of pop on your 'freezer' and cool it down to about minus 2c. Use a thermometer to check the temperature. Then unscrew the bottle-cap and let out some of the gas, but not the liquid.
In less than ten seconds, the liquid in the bottle will freeze. Why? In the same way that adding salt to water lowers its freezing-point and prevents ice forming at temperatures hovering around 0c (which is why we salt the roads in winter), so carbon dioxide dissolved in a drink also lowers its freezing-point.
That's why the pop doesn't freeze when you initially lower its temperature to minus 2c. But when you allow some of the CO2 to escape, the freezing-point swiftly becomes higher than the temperature of the water. And, hey presto, instant ice.
Ice
MAKE A FORCEFIELD
You will need: an empty fizzydrink can, a piece of polystyrene
Rub the polystyrene on your hair for a minute. Wave the polystyrene near the can. The can will move towards you. This is because electrons - the negative part of an atom - can be transferred on to other materials on contact. Polystyrene 'steals' electrons from materials when it touches them. By putting it on your hair, you are giving the polystyrene a negative charge. The can is positivelycharged. Like charges repel, so the polystyrene forces the electrons in the metal to the far side of the can. This makes the side of the can nearest the polystyrene positive. Opposite charges attract, pulling the can towards the polystyrene.
CONFUSE YOUR SENSES
You will need: water, a few ice cubes, three large bowls or washing-up basins
Fill bowl number one with cold water and a few ice cubes. Fill bowl number two with lukewarm water. And fill bowl number three with hot (but not scalding) water.
Put one hand in the hot water and the other in the cold water, and keep them there for one minute. Then plunge both hands into the bowl of lukewarm water. Although both hands are immersed in water of the same temperature, they will feel different. The one that's been in warm water will feel cold, and the one that's been in cold water will feel warm or hot.
This is because our senses are relative - they don't act as accurate and objective thermometers. Instead, they measure how things change - in this case, the temperature of the water relative to the temperature of your hand.
This process, called adaptation, also explains why we get used to odours after they've hung around for a while.
Spin . . . AND YOUR BRAIN
Ingredients: swivel chair, friend
Sit on the chair, bend your head down so that one ear is covered by your shoulder, stick your legs out and get a friend to spin you round for about 30 seconds. Then try to stand up and walk. You'll probably stagger forwards or backwards.
But if you try the same experiment with your head upright, you'll fall sideways. Why the dizziness?
The inner ear contains tubes of fluid - semi-circular canals - that monitor balance. When you spin in the chair, the fluid swishes around in the tubes, continuing for a while after you've stopped. This tells your brain you are still moving, even though the brain thinks you've stopped. The conflict of information causes you to stagger.
MAKE A SUBMARINE
You will need: 2-litre plastic bottle, water, unopened ketchup sachet, Blu-Tack
Fill the bottle to the brim with water and add an unopened ketchup sachet. The sachet is your submarine - it should just about float. If it's too buoyant, weight it down with Blu-Tack. Screw on the bottletop tightly. Squeeze the bottle hard and watch the submarine dive to the bottom.
It was Archimedes who realised that when something floats, it must be lighter than the amount of water that would fit into the same volume.
When you squeeze the plastic bottle, you apply pressure to the water inside. But liquids are difficult to compress, so the pressure from your squeeze is transmitted to the sachet, which contains a small amount of gas (nitrogen). The pressure compresses the nitrogen, which makes the sachet more dense than water so it dives to the bottom. A submarine works similarly, adjusting the volume of air in its buoyancy tanks.
Meteor LAUNCH YOUR OWN METEOR STRIKE
You will need: cooking tray, flour, sieve, cocoa, Maltesers
Fill a cooking tray with sieved flour one inch deep. Sieve some cocoa (which will stand in for the Earth's top-soil) on to the flour.
Drop some Maltesers ('meteorites') into the tray. The Maltesers will end up deep in the flour. Some of the flour will be thrown upwards, covering the cocoa powder in a circle about 5cm wide.
This shows what a meteor does to the Earth. When it strikes, it disturbs the earth even underneath where it lands. Meteors fly through our atmosphere at around Mach 25 (25 times faster than the speed of sound - about 20,000 miles per hour). They gain kinetic energy as they fall and that energy causes the meteor to impact with huge force. The disturbed earth - below the Earth's surface - covers the surface around the edge of the crater.
LAUNCH A MATCHSTICK SPEEDBOAT
You will need: one matchstick, knife, bowl of water, washing-up liquid
Cut a matchstick along its length to make a Y-shape, then float it in a bowl of water. Add a drop of washing-up liquid to the split end, and you'll see your matchstick whizz across the water. The reason is surface tension. Water molecules are linked together - but when the washing-up liquid is added, it breaks the linkages between the molecules. As the tear in the molecules enlarges, the surface tension pulls the matchstick towards the sides of the bowl.
MAKE SUGAR GLOW IN THE DARK
You will need: sugar lumps, pliers, pitch-dark room
Take the sugar and pliers into a dark room and wait for two minutes so that your eyes adjust and become sensitive to small amounts of light. Then crush the cubes with the pliers - and sit back and enjoy an incredible light-show.
You should be seeing dancing flashes of blue-green light. These are called triboluminescence. There is no absolute consensus as to why this phenomenon occurs, but it's thought that smashing the sugar crystals creates fragments with uneven electrical charges. When the charges recombine, they discharge a flash that looks like a mini bolt of lightning.
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