# Q & A: Conduction, Convection and Radiation - Moving Heat

Q:
- Amos (age 16)
Sioni Secondary, Singapore
A:
Amos -

Conduction, convection and radiation are the three major methods of heat transfer. That is, they are three different ways that heat can spread.

Conduction is probably the simplest to understand. If you say that something is hot, then what you are really saying is that the atoms inside of it are moving around a lot. Even in a solid like a metal, the atoms can move back and forth quite a bit. When the atoms move, they bump into the atoms next to them, making them move. This starts a chain reaction and the heat spreads through the whole object. This is what's happening if you've ever set a pan on the stove. The handle gets warm even though only the bottom touches the burner because the metal conducts the heat. As it turns out, in metals heat is conducted not so much by wiggling atoms, but mostly by wiggling electrons (the idea is the same, though).

Convection is a bit trickier. Convection is a way for heat to move through a fluid, like water or air. You may have heard of the phrase 'hot air rises.' This is convection. Hot air (or hot water, etc.) is less dense than cooler air. So if you heat up the air at ground level, it will rise up into the sky to be replaced by cooler air moving downwards. This creates something called 'convection currents,' which are one of the things that birds use to rise up into the air. To see this at home, you can get a clear ice-cube and drop it into a glass of warm colored water (food coloring is fine). You should be able to see how the warm (colored) water moves upwards while the cold (clear) water melting off the ice cube moves down.

Radiation has to do with light. Sounds weird? Not really. The light that you see is actually made up of something called electromagnetic waves. The electromagnetic waves that carry the kind of heat that we are most familiar with (from a heat lamp, for example) have longer wavelengths than the waves that make up visible light and hence they are often called "infra-red". When something is hot, like the burner on your stove, it releases some of its energy in the form of these infrared waves. The waves travel through the air until they hit something, which gets heated up. This is why you can feel the heat from your stove even if your hand isn't actually touching it. The burner literally 'radiates' heat.

-Tamara

(published on 10/22/2007)