Science Questions

Why do mellons keep cool in the sun?

On holiday, I bought a massive green melon on my way to the beach. We left it in the sun but after 3 or four hours when we cut it open to eat it was still cool inside. How did this happen? Jettan

There are a few things contributing to this, firstly, a melon is roughly spherical, and a sphere has a low surface area for it's volume.  For the melon to heat up, the sun must shine on its surface, and so in this situation, there's not much surface conpared to the volume of the melon.  Also, a melon contains a lot of water, which has a high 'specific heat'.  This means that you need to put lots of energy in to raise the temperature just a little.  Even if the water does heat up, the flesh of the melon will not let the water move around inside, so the heat is not spread through, but needs to pass from one cell to the next.

It's also possible that the melon loses water by evaporation, which would also help to cool it down.

September 2007