conductionConduction is the name of the form of heat transfer which happens in solids. Here particles are arranged close together and can only vibrate in a fixed position so energy can be passed from one end of a material through it by the action of the more energetic particles vibrating and colliding with others to pass on energy - a bit like a mexican wave travels around a sports stadium! Metals are good conductors also because they have free electrons which add to the vibrating and colliding particle effect passing on energy by collisions too.
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convectionFluids are liquids or gases where these states of matter allow the particles to flow. This allows a convection current to transfer heat energy due to moving particles.
The warmer particles gain energy from a heat source and move apart more hence reducing density. The higher density areas will fall to the bottom of the container allowing the warmer areas to rise. This sets up a current or cycle as hotter less dense areas are pushed up out of the way by the heavier dense parts. |
radiationHeat transfer by radiation does not need any particles to move. Instead the heat energy is transferred by an electromagnetic wave called infra-red radiation from the hotter object to the cooler object.
It can happen through the vacuum of space allowing heat from the Sun to arrive on Earth. Humans haven't evolved to see in infra-red although we can detect heat energy due to radiation using our skin. |
When liquid particles gain sufficient energy they can change state into a gas and escape. Some particles will manage this below the boiling point of a liquid and they seem to disappear into the air but that is because they are so small we can't see them. An evaporating liquid will cool down as the escaping particles which had more than average energy leave a substance behind with less energy - in other words, cooler.
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Condensation is the opposite change of state process to boiling and evaporation so here the particles lose energy and cool from highly energetic gas particles to slower, more closely packed liquid particles. We can see droplets forming on a window or the side of a cool glass when water vapour in the air cools in the surface.
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