In liquids and gases: convection
Water is a poor conductor. Yet a pan of water heats up fast. How?
Step 1 of 4
- A pan of water is warmed at the bottom.
- The warm water at the bottom rises.
- Cooler water from the top sinks to take its place.
- This goes round and round. Soon all the water is warm.
Moving water carries the heat to all of the pan.
Warm water takes up a little more room. It is lighter for its size, so it rises.
The new word
- Convection — heat carried by a moving liquid or gas.
The rule
In a liquid or a gas, the warm part rises. The cooler part sinks to take its place. This is convection.
Air carries heat too
A breeze is a gentle wind. By day, land heats faster than the sea. Warm air over land rises. Cool sea air moves in: a sea breeze. At night the air moves the other way: a land breeze.
Watch out!
Warming a water tank from the top does not mix the water. Warm water is lighter for its size, so it stays on top. The bottom stays cold for a long time.
Now try it. Slide the heater up the tank. Count the warm layers.
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