Falling candle

This intriguing demonstration shows what happens when the effects of convection are 'cancelled out'. A candle is fitted to the inside base of a tin; the candle is now lit and the tin is dropped. The tin should be big enough to provide enough oxygen, but the flame still goes out.

Theory: Since there is effectively zero g in the can one of the conditions for convection does not apply - that is, although the hot waste gases in the candle flame have expanded they do not rise away from the flame since they and the flame are both falling. This means that there is no convection in the can. The candle therefore tries to burn in its own waste products and fails. Helen Sharman tells of how she had to sleep in draught from a fan in the Russian spacecraft so that she didn't suffocate in her own exhaled breath. Michael Foale had a similar experience in Mir.

Age range: 11-14

Apparatus required: Tin can Candle Matches Protection for the floor (a piece of old carpet) TV camera if available.

Convection and a tea bag

This is a fun experiment to demonstrate convection especially if you use the £10 note!

Take a tea bag, slit one end open and remove the tea. Shape the bag into a cylinder and stand it on a sheet of paper on the bench (a heat resistant mat underneath the paper is not really necessary but might be a good idea the first time you try this). Set light to the top of the bag and wait.

The flame will burn downwards sending a fine stream of ash into the air. As it nears the paper the tea bag continues burning but by this time the upward convection current is sufficient to draw the last remnants of the bag upwards and they simply float away leaving the paper untouched.

Replacing the sheet of paper with a £10 note makes the demonstration even more exciting but if you try it is at your own risk!

Age range: 11-14, 14-16, 16-19, Adult
Apparatus needed: Tea bag Matches Heat resistant mat Sheet of paper £10 note – OPTIONAL!

Communication

The idea of this experiment is to demonstrate communication, or the lack of it, between a group of people.



Six people with a long light dowel rod should stand in two equal rows facing each other. They each support the rod by their two forefingers. The idea is to lower the rod to the ground. It sounds simple but their fingers must remain touching the cane.

It is surprisingly difficult. In their desire to keep touching the cane the result is that the dowel usually goes upwards rather than downwards.

Age range: any

Apparatus required:
People A piece of dowel rod (at least 2m long)

Falling can and water

Take a tin can and drill a hole in the bottom.
The size isn't critical but two or three millimetres in diameter will be fine. Put your finger over the hole and fill the can with water. Now drop the can - the water stays inside. This is much as you would expect, since all objects accelerate downwards at the same rate if air resistance is ignored. Now repeat the experiment but drop the can after you have allowed some of the water to start streaming out. What happens to the water? It looks as if the can is continuing to empty itself, but this would mean that the water is falling with a greater acceleration than g. This is impossible of course! The can and the water both accelerate at the same rate, g, and the can has the same amount of water in it when it reaches the ground as it had at the start of the drop.

Age range: 14-18

Apparatus required:
Bowl or bucket Tin can with hole

Collapsing bottle and air pressure

This demonstration of atmospheric pressure is very simple and direct and avoids heating cans of air! Completely fill a plastic squash bottle with water - bigger bottles are more impressive. Put a bung in it with a glass tube in the centre and attach a 2 m length of rubber tubing to the tube - more if the height of your lab will allow it. Get someone to hold the end of the tube closed while you climb on a bench and upend the bottle with the rubber tube dangling vertically downwards. Now open the lower end of the tube. As the water runs out the bottle will be squashed flat by the pressure of the air on the outside! The long tube gives a bigger pressure difference between the top and bottom of the water column and also prevents air leaking in.

Theory
Pressure difference between the two ends of the water column of height h = rgh where r is the density of the water.

Age range: 11-13

Apparatus required:
Plastic bottle with rubber tube fitted to a bung in its neck Water Bucket

The wire coat hanger and circular motion

Pull open a wire coat hanger so that it forms a square. File the end of the hook flat and then bend the hook until it points towards the opposite corner of the square. Balance a 1p coin on the hook, put one finger in the corner of the square opposite the hook and then spin the coat hanger in a vertical circle - the coin stays in place! This is a very simple but excellent demonstration of centripetal force.
The force of the hook on the penny always acts towards the centre of rotation. The present record is five 1p pieces stacked on top of each other. With only one penny balanced and with great care I have once even been able to bring the coat hanger to rest without the penny falling off.

Age range: 14- 18

Apparatus required:
Wire coat hanger with filed end Pile of small coins

Mousetraps and chain reactions

This lovely (although potentially painful) demonstration is a splendid simulation of a nuclear chain reaction. Set up a number of cocked mousetraps side by side in a rectangle (a dozen will work well if you can manage it!) to represent uranium nuclei. Put a couple of polystyrene balls representing neutrons on each one.
Throw in another polystyrene ball (neutron) to start the chain reaction. One mousetrap goes off - this sets off others and so on!
The balls are shot all over the lab (Fast neutrons). Spacing out the mousetraps gives an idea of shape of fuel rods and the way a chain reaction can fail.


It works best if the mousetraps are placed on the lid of a cardboard box to give a good "linkage" between one "fission" and another.


DANGER: MIND YOUR FINGERS!

Age range: 16-18

Apparatus required:
Mousetraps Polystyrene balls Cardboard box

Metal cup cake holders and the Van de Graaff generator

A lovely demonstration of the repulsive force between charges of the same sign. Put a pile of metal cup cake holders upside down on top of the large dome of a Van de Graaff generator and switch the machine on. As the charge builds up the top holder will drift off – the repulsion is just bigger then the weight of the holder. This is then followed by the next one down and so on giving a "rain" of holders.

Alternatively a plastic bowl holding puffed wheat can be taped to the dome. The puffed wheat flies out when the machine is turned on!

Age range: 11-18 depending on treatment

Apparatus required: Van de Graaff generator
About ten cup cake holders