Convection
Heat carried by moving liquid or gas. Warm fluid expands, becomes less dense and rises. Cooler fluid sinks to take its place.
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Analogy
A hot-air balloon rises because the warm air inside is lighter than the cool air around it.
In practice
A radiator warms a room by making warm air rise and cool air sink, setting up a loop.
Practice
Flashcards
- How does convection happen?Warm fluid expands, becomes less dense and rises. Cool fluid sinks.
Interview questions
- Describe how heat travels from a radiator to warm the whole room.
- Air touching the radiator is warmed by conduction
- Warm air expands, is less dense and rises
- Cool air sinks to replace it, forming a convection current
- Some heat also travels as infrared radiation
Questions people ask
Why does hot air rise?
When air is heated its particles move faster and spread out, so the same mass fills a bigger volume. That makes the warm air less dense than the cool air around it, so it floats upwards, just as a cork rises in water.
Why can convection not happen in a solid?
Convection needs particles that can move from place to place carrying energy with them. In a solid the particles are locked in position and can only vibrate. That is why convection only happens in liquids and gases, which are called fluids.