# Physics AQA - Unit 1

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Heat Energy

All objects either emit or absorb heat energy. As humas, our body tempreture is much higher than the outside and therefore we emit heat energy. As you know when things become hotter the particles gain more energy and therefore move around faster.

If we were to heat a solid, the particles could gain a certain amount of energy and then turn into a liquid. If we continued to then heat this liquid it would eventually turn into a gas.

Conduction

Conduction is the process by which heat energy is transferred from particle to particle. It usually occurs in metal and solids.

As you can see, in solids the particles are vibrating. By adding heat energy to one particle, it makes it vibrate more, which in turn hits other partices also making them vibrate more and therefore energy is conducted through the object.

Conduction works best in metals as there are free electrons which can help carry the heat energy, objects like wood and plastic do not have free electorns and are much poorer conductors of heat.

Convection

Convection, is the way that heat energy is transferred in liquids and gases. It involved one particle gaining hear energy and being able to move faster than the particle surrounding it.

Warmer air is less dense than cooler air, therefore warm air rises up and cold air falls down. The same rule applies in liquids.

If you are heating water on a bunsen burner, the heat will make the water particles at the bottom of the beaker heat up first which causes them to rise. As they rise the cooler water particles which are yet to be heated up fall to the bottom of the beaker so they can also be heated.

The same applies to a room being heated by a radiator.

Evaporation

If the particles in a liquid have enough energy and are moving fast enough then they will be able to escape from the liquid and turn into a gas. This is called evapouration. The particles take energy with them therefore the tempreture of the liquid drops, this is how sweating works - heat energy from the muscles in the body cause the water in the sweat to evapourate cooling the body as heat energy is taken with it.

Condensation

Condensation is the oppisite of evapourtion, it is where particles lost energy and turn from a gas to a liquid. This usually happens when hasses hit cold surfaces such as cold windows. The energy that the gas particles lose goes into the cold surface.