Wind in a bowl - convection

Make your own model weather system in a bowl of water.

What you need

What to Do

What may Happen

You should find that coloured water rises from the bottle of hot water, and will eventually fall back down again, and that you see coloured water falling around the sides of the ice cube.

What is going on?

When most fluids, including air and water, gets hotter they expand_^†, this means that the same volume of fluid weighs less, and it will float on the fluid around it. This is the reason that the hot water floated upwards, and cold water from the ice cube is more dense so it sank to the bottom of the bowl.

This produces a circulation, hot fluid rising over a heat source cooling at the top and falling again somewhere else in a process called convection. Air does the same thing, so if you get hot air and smoke coming out of a chimney rises, and air over a particularly hot piece of ground on a sunny day will rise up in a thermal. The cold air rushing in from the sides of the thermal is a wind. In fact the energy to drive all winds comes from convection.

†Water is actually slightly more complex than this, if it is between 0°C and 4°C it actually expands as it cools, which is related to ice being less dense and therefore larger than the same mass of water

Written by Dave Ansell