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 4: The disappearing O.

Here I've got a really great and surprising example of how your brain makes stuff up.

What you'll need:
Nothing really, just this page. Or you could draw the X and O on a bit of blank paper.

          X                                                                    O                             

What to do:
1) Close your left eye.
2) Look at the X, but pay attention to the O.
3) Slowly move towards the screen.
4) When you are about 15cm or 6 inches from the screen (you'll need to be closer on a small screen) the O should disappear.

What's going on?
The retina at the back of your eyes is covering in cells that are sensitive to light. But at the spot where the optic nerve (which connects your eye to your brain) is attach to the retina there are none of these cells. Any light that falls on this blank patch isn't registered. Which means that when the light from the O hits that spot you don't see it.

So how come we don't notice this blind spot all the time? Well you're brain is pretty amazing, it just makes up some stuff based on what it sees around the blind spot and clones it in the space. There is white space around the O and thats what your brain sticks into the gap. You can see just what a good job your brain does by doing the same experiment on the X below.

Once again close your left eye and pay attention to the sentence 'Nothing missing is there?'. Nothing missing is there?

X                                                 Nothing missing is there?

Number 3: The flaming orange

Since we've already got our candle out I thought we'd make more use of it.

You'll need:

• A candle.
• Some matches or a lighter.
• A thick skinned orange (navel oranges work well) or other citrus fruit.
• A knife.

Safety:
We're using fire again so keep that adult close by and you'd best get them to peel your orange as well.

What to do.
1) Start by peeling the orange. Keep the peel handy, eat the orange.
2) Hold some peel between your fingers and thumb with the orange side facing away from you.
3) Squeeze the peel, you should see little droplets spraying out of it.
4) Light the candle and dim the lights.
5) Now get another piece of peel and squeeze it towards the candle flame.
6) You should see something like this.

Cool ain't it!

What's going on?
Citrus fruit peel is full of an oil called limonene, which is what the droplets are made of. In fact its this stuff that makes the peel smell so nice. Limonene is really flammable, so when you squeeze it into the flame is catches fire and produces that fab flamethrower effect.

Hold on a mo I hear you yell. How come lemon and orange peel smell different if they contain the same chemical that makes them smell? Good question. We it turns out that the limonene in oranges is the mirror image of limonene in lemons and even though they have exactly the same chemical formula our noses can tell the difference.

Number 2: The jumping flame trick

This makes a great 'magic' trick for birthday parties or boring dinner parties for that matter.

What you need:

• A candle
• Some matches

Safety:
Flames are involved so best make sure there is a sober adult present.

What to do.
1) Light the candle and let it burn for a minute or until the wick is surrounded by a puddle of liquid wax.
2) Blow out the candle.
3) Hold a lit match in the candle's smoke a couple of centimetres above the wick.
4) Bingo, the candle should suddenly reignite.

What's going on?
To set things alight you need oxygen (which comes from the air), an ignition source (the flaming wick) and some fuel (the paraffin wax in the candle). The flame melts the wax which is then drawn up the wick and so provides the flame with a ready source of fuel. When you blow the candle out the wick contains some of this liquid wax and the glowing end of the wick heats the wax still further so that it vaporises (to a gas) and drifts off with the smoke. The gaseous wax is flammable so when you put a match in the smoke you ignite the gas, the flame travels down the smoke trail and then reignites the wick. It all happens too fast for you to see so it looks like the candle spontaneously relights when you hold a match above it.