Take a small bottle and a large clear bowl or tank. Fill the tank three quarters full with cold water. Fill the small bottle with hot water, and add a couple of drops of food colouring. Put a top on the bottle, and make a small hole in the top. Lower the bottle into the tank with your finger over the hole to stop any water escaping.

Settle the bottle on the bottom of the tank with the top submerged and remove your finger.

Observe what happens. The hot water will rise through the hole. As it is coloured you can observe it moving to the top of the tank.

Repeat the experiment using cold water in the bottle and warm water in the tank.

What happens if you carefully pour the cold coloured water into the bottom of the tank?

Finally, make a hot air detector. Take a piece of A4 paper and cut out a circle with a diameter that is as wide as the paper’s width.

Starting from the middle of this paper disc, mark out a spiral snake, making sure that the body is at least 1cm wide. Cut out the spiral, and decorate.

Attach a thread to the inside end of the snake and suspend it above a table lamp, making sure it is not in a draught and will not touch the light bulb.

Turn the lamp on and watch what happens. The snake should spiral round as the air, heated by the bulb, rises.

Take two similar table lamps and put an energy-efficient light bulb into one and a normal light bulb into the other. Suspend a “snake” above each lamp, and turn them on.

Less heat will be given out by the energy-efficient bulb, and the snake above it will not move as much as the one above the normal bulb.