Monthly Archives: May 2011

Namaqua chameleon

The Namaqua chameleon (Chamaeleo namaquensis) is really good at physics, even though he probably doesn’t realise it.

During the morning, when the Namib Desert in which it lives is colder, the chameleon turns its skin black so that it absorbs sunlight more efficiently and heats up quickly.

They can even split their colouring along their spines, white on one side and black on the other; absorbing heat on the black side whilst not radiating it on the white side.

The clip is taken from the BBC David Attenborough series Life.

Boiling point and pressure

A vapour is created when a substance forms a gas at a temperature below its boiling point; the vapour pressure of a liquid is the pressure of this vapour. A liquid boils when the vapour pressure of the liquid is equal to the atmospheric pressure of the air above it.

You can therefore boil a liquid in two ways: by heating it so that the vapour pressure increases to match the atmospheric pressure; or by decreasing the atmospheric pressure until it matches the vapour pressure at whatever the ambient temperature is.

In this video you can see me boiling water at room temperature: a beaker full of water at room temperature is placed in a vacuum chamber and the pressure lowered until it boils – the pressure gauge is on the right of the picture.

Notice how I can put my finger in the water both before and after boiling without scalding myself. It’s said that it’s impossible to make a good cup of tea at the summit of Mount Everest because water boils at only 70.4°C and this isn’t hot enough to properly brew tea.