Heat and Energy

Energy is the ability to do work or to cause change. It comes in many forms: light, sound, movement, heat, electrical and chemical energy. Nothing can happen without energy — it powers your body, the weather, machines and the whole universe.

One of the most important rules in all of science is the conservation of energy: energy cannot be created or destroyed. It can only be changed from one form into another, or moved from place to place. The total amount of energy always stays the same.

Heat travels in three different ways. The first is conduction: heat moving through a solid material. If you put a metal spoon in hot soup, the handle soon becomes warm because heat is conducted along the metal. Metals are good conductors of heat.

The second way is convection, which happens in liquids and gases. When a liquid or gas is heated, it expands, becomes lighter and rises, while cooler liquid or gas sinks to take its place. This sets up a circular flow called a convection current — it is how a radiator warms a whole room.

The third way is radiation: heat travelling as invisible waves that can even cross empty space. This is how the Sun's warmth reaches Earth across millions of kilometres of space, where there is nothing to conduct or carry it.

Energy is constantly changing from one form into another. When you rub your hands together, movement energy turns into heat energy and your hands warm up. When a torch is switched on, electrical energy turns into light energy and a little heat. Each of these is an energy transfer.