Number 15: The 'impossible' balancing forks

Here's a trick that just looks impossible. Even when you know what's happening it just doesn't look right.

You'll need:

• 2 identical forks
• Cocktail sticks or toothpicks
• A glass
• Matches

Safety:

Matches are involved so get adult supervisions.

What to do:

1. Lock the tines of the forks together.

2. Jam a cocktail stick through between the tines of the fork so that is sticks about 1 cm out the back.

3. Pick up the forks and place the cocktail stick over the rim of the glass with the handles pointing in towards the glass. Find the spot where the forks balance. 

This already looks pretty amazing. But it gets better!

4. Now light the end of the toothpick thats pointing towards the inside of the glass. 

So what's going on?

It just looks all wrong doesn't it? But the explanation is really quite simple. Half the weight of the forks is in front of the rim of the glass and the other half is behind the rim of the glass. So everything balances nicely.   Sometimes physics just doesn't look right.

Number 14: Elephant's toothpaste

Here's a great example of biochemistry in action.

You'll need:

• A bottle of hydrogen peroxide. You can get this from most pharmacists. Try and get 9%, but 6% will do.
• Dried baker's yeast.
• Washing up liquid.
• An empty plastic bottle (500ml or so).
• A glass with a 20ml of water in it.
• A teaspoon.

Safety: 

Hydrogen peroxide is a mild bleach (which is why its used to make your hair go blond). Be careful with it and don't get it in yours eyes. Best get some adult supervision for this one. And it makes a bit of a mess so do it outside.

What to do.

1. Put about 2 teaspoons of yeast into the glass with the water. Mix it about until it looks like brown muddy water.

2. Squirt about 2 teaspoons of washing-up liquid into the plastic bottle.

3. Pour 50ml of hydrogen peroxide onto the washing-up liquid.

4. Pour the yeasty water into the plastic bottle. Stand back and ...

What's going on?

Remember the chemical formula for water? H₂O, meaning water is made from two hydrogens and one oxygen. Well hydrogen peroxide is almost the same except its got an extra oxygen, so its formula is H₂O₂. But whilst water is very stable (remember how we needed to put electricity through water to break it down in the hydrogen and oxygen), hydrogen peroxide is unstable, it slowly decomposes to water and oxygen. However when the yeast is added to the hydrogen peroxide that extra oxygen gets released really quickly and you end up with loads of oxygen gas (the washing up liquid is just there so that the gas gets trapped in all that foam). 

So why does adding yeast result in the oxygen being released so quickly? Well yeast contains an protein called catalase. It looks like this. 

Catalase is a type of protein called an enzyme. Enzymes¹ speed up specific chemical reactions. In this case the reaction is:

2 H₂O₂ → 2 H₂O + O₂

Which is just a way of saying that 2 hydrogen peroxide molecules turn into two water molecules plus 1 oxygen molecule. The really astonishing thing about catalase is how fast it works. One catalase molecule can break down 40 million molecules of hyrodgen peroxide every second!

¹ The word enzyme comes from the greek ενζυμον, meaning "in yeast". Plus things that speed up chemical reactions are called catalysts, hence the name catalase. So if you follow the etymology of these things you end up going around in circles.

Number 10: Polishing the silver

There's all sort of potions and polishes that you can buy to clean up the silver. Don't buy any of them. Because you can find everything you need to get the best cutlery sparking again in your kitchen cupboards.

What you'll need:

• Bicarbonate of soda
• Aluminium foil 
• A cup or glass
• Some tarnished silver spoon (its best if its solid silver, it will work with silver plated stuff, but you run the risk of removing the plating)

What to do:

1. Put a heaped teaspoon of bicarb into the glass.

2. Tear up 10 to 20 bits of foil and add them to the glass.

3. Put the spoon in the cup

4. Pour on hot water. Water from the hot tap will do fine. 

5.Stir and leave for 5 minutes.

6.Take the spoon out and inspect it. All the tarnish will have disappeared. 

Before

After

What's going on:

There's some pretty niffy chemistry going on here.  First lets dispel a little myth, the tarnish is not due to a reaction with silver and oxygen like a lot of people claim. Iron reacts with oxygen to make rust, but silver tarnish is something different. Silver tarnishes when it reacts with sulfur containing chemicals (usually hydrogen sulfide, which smells like rotten eggs) to produce silver sulfide. Eggs are particularly high in sulfur which is why they make your silver tarnish so quickly.

That's the easy bit. How the aluminium and bicarb work to clean the silver is a little more complicated.

Lets take a look at the chemicals that we start off with. You've got silver sulfide (the tarnish), sodium bicarbonate (the bicarbonate of soda), aluminium  hydroxide (the foil is actually covering in a layer of this, the aluminium itself is underneath and we need to get at it).

Step 1: The bicarbonate reacts with the aluminium hydroxide and turns is back to aluminium.

Step 2: The aluminium reacts with the silver sulfide to make silver and aluminium sulfide.

and that leaves you with nice clean silver.

Number 9: The Camera Obscura

In my opinion a home made room sized camera obscura¹ beats TV hands down. Its really simple to make one and the results are just extraordinary. Me and the kids love lying on the bed watching the outside world projected onto the walls and ceiling.

What you'll need:

• A sunny room, preferably with one window.
• A bright day.
• A roll of thick plastic refuse sacks.
• Masking tape.
• Scissors.

What to do.

1) Cut open the sacks and stick them together into a sheet large enough to cover the window(s).

2) Tape the sheet of sacks up against the window.

3) Cut a 1cm hole in the middle of the sheet.

4) Sit back and let your eyes get used to the dark.

5) After a few minutes you should start seeing the outside world projected (upside down) all around your room. Cars will wizz along the walls and you'll see people in the street walking along your ceiling!

View inside the room with the camera obscura set up. It you want to take a photo like this you'll have to use a long exposure (2-4 seconds should do the trick).

For comparison here's the same view out the window.

What's going on?

Basically we've just made ourselves a great big pinhole camera! Light travels in a straight line and crosses over as it goes through the hole in the bags. The light carries on until it hits the wall in the room. So everything on your wall appears upside down.

There are loads of camera obscura's you can visit all over the world. My favourite is the observatory near the Clifton Suspension Bridge in Bristol. It has splendid views of the Bridge and the City.

¹The term camera obscura comes from the latin for 'dark room'. So the word camera is actually just latin for 'room'!

Number 8: Splitting water

If there's a chemical formula we all remember it the one for water, good old H₂O;  two hydrogens and an oxygen. Well its really easy to split water up and liberate the hydrogen and oxygen as gases. The process is called electrolysis and all you need is....

What you'll need:

• One 9V battery (those square ones)
• 2 lengths of insulated wire
• A pencil
• A bowl of water
• Table salt
• A box cutter knife

Safety:
Watch out with the knife. Best get an adult to use it.


What to do:
1. First you need to get the lead ¹ out of the pencil. To do this its best to carefully whittle the pencil with a pen knife or box cutter.
2. Strip about 2cm of the insulation from both ends of both wires.
3. Take one of the wires and wrap one end around a terminal of the battery and the other end around the graphite from the pencil. Repeat with the other wire. BE CAREFUL not to short circuit the battery by letting a bit of wire touch both battery terminals.
4. Dissolve a teaspoon of salt in the bowl of water.
5. Put the graphite rods into the water.

6. Take a close look at the graphite rods. You should notice bubbles forming on them.

What's going on?
We all learnt at school that water is made up of 2 hydrogen atoms and 1 oxygen atom, so a molecule of water has the formula H₂O. But this isn't the whole picture, because in your bowl of water a lot of it isn't actually in the molecular (H₂O) form. Instead it splits up into H⁺ and OH^-. These are called ions. The + symbol on H⁺ means the hydrogen is positively charged because its missing its electron, meanwhile the - symbol on the OH^- means the OH ion is negatively charged because it has gained an electron.

Electricity it basically made up of moving electrons and ions. So electrons flow out of the negative terminal of the battery and in at the positive terminal. In the experiment we've just done the electrons flow down the wire to the graphite electrode and then join up with the H⁺ , this turns the ion back into molecular hydrogen (H₂). Hydrogen is a gas so it forms as bubbles on the electrode.  The opposite happens on the other electrode, here the extra electron on the OH^- flows up the wire leaving another H⁺ and molecular oxygen (O₂) gas.

You might have noticed that there are more bubbles on one electrode that the other. Thats because there is twice as much hydrogen than oxygen in water, so you also make twice as much hydrogen gas.


What's the point?
Hydrogen could well be the fuel of the future. The idea is that when we run out of fossil fuels we'll be able to replace petrol and oil with hydrogen. And this is how the hydrogen will be made. The only problem is that we need a source of electricity to split the water up and at the moment most of our electricity comes from burning fossil fuels. But if you hook up our setup to a wind turbine or a solar panel then the problem is solved!






1 Actually its graphite, not lead in pencils. And contrary to popular belief pencils never had lead in them. The name comes from 'black lead' which was mined near Keswick in the UK's Lake District. The Grey Knotts mines in the hill around Keswick are the only natural source of solid graphite in the world. Which meant that until an artificially way of making solid graphite rods was invented the lead in every pencil in the world came from Keswick.

Number 7: The magnetic grape

You remember how in school your teacher told you that only things with iron in them are magnetic; spoons, nails that sort or thing? Well your teacher didn't get that quite right. Because it turns out that  everything is magnetic to some extent. Even grapes. And that's why this happens:

If you want to try this yourself..

You'll need:

• 2 grapes
• A wooden skewer (NOT A STEEL ONE)
• A pin
• Something to stick the pin through so that it points upwards on a stable base. I used an old film canister, but bit of cork would do just as well.
• A neodymium magnet. The stronger the better but you probably want one with at least 20 Kg pull.

Safety:

THIS IS REALLY IMPORTANT

The neodymium magnets are really powerful. So...

1. Don't let kids play with them.
2. Don't put them near your credit cards, phone, watch or any other electrical equipment.
3. Don't put 2 magnets anywhere near each other because they'll fly towards one another, shatter and send chunks flying.
4. If you have any medical implants don't go anywhere near them.
5. Read the safety instructions that come with the magnets.

What to do:

1. Push the 2 grapes onto either end of the skewer

2. Push the pin through the cap of film canister, so that its pointing upward. Put the cap back on the canister.

3. This is the tricky but. You need to balance the skewer and grapes on the point of the pin. If you get close then adjust the balance by pushing one grape further onto the skewer.

4. Once you've managed that just put the edge of the magnet near one of the grapes and watch them spin.

What's going on?

There are actually numerous types of magnetism. At school we only learn about ferromagnetism. Then there's paramagnets (which are attracted to ferromagnets) and diamagnets (which are repelled by ferromagnets). These 2 types of magnetism are much weaker than ferromagnets so you generally can't see the effect. Which is why you need a set up like this and a powerful magnet to observe it.

Since the water in the grape is diamagnetic its repelled by the strong ferromagnet near it and that makes the grapes spin on the pin. 

You can demonstrate the same principle another way shown here.

Incidentally this effect is central to how MRI scanners in hospitals work.

Number 5: The rolling can

You can have a lot of fun with static electricity and here's a great example.

What you'll need.

• A balloon
• An empty drink can.  It needs to be aluminium. It may have a little sign on it that says ALU or try sticking a magnet to it. If the magnet sticks then its steel, if not then its probably aluminium.
• A hairy head (without any gel or hairspray) or a woolly jumper (thats a sweater if you are in the USA).

What to do.

• Blow up the balloon and tie a not in it.
• Rub the balloon against your hair (or woolly garment).
• Lie the can down on a flat surface.
• Hold the bit of the balloon that your were rubbing near the can.
• The can will roll towards the balloon!

What's going on?

Rubbing the balloon on your hair charges it up with static electricity which makes the balloon negatively charged. When you put the balloon near the can it pushes electrons (which are also negatively charged) to the other side of the can. This makes  the side which is nearest the balloon positively charged. Positive charges are attracted to negative charges so the can moves towards the balloon.