Reducing Unwanted Energy Transfers

Not all energy transfers are useful.

When a machine is working, some energy is often wasted by friction. When a house is heated, some energy is wasted because it escapes to the colder surroundings. In both cases, energy has not disappeared, but it has been transferred in a way that is not useful.

In GCSE Physics, you need to know some ways of reducing these unwanted energy transfers.

Reducing Energy Wasted by Friction

Friction happens when two surfaces rub against each other. It can be useful, for example when shoes grip the floor, but it can also waste energy.

In machines, friction between moving parts can transfer energy to the thermal energy stores of the parts and the surroundings. This means the parts heat up and some useful energy is wasted.

One way to reduce this is by lubrication.

Lubrication means adding a substance such as oil or grease between moving parts. The lubricant helps the surfaces slide over each other more easily. This reduces friction, so less energy is transferred as heat.

A good example is a car engine. Engine oil reduces friction between moving metal parts. This helps the engine run more smoothly and reduces wasted energy.

Reducing Energy Loss from Buildings

Buildings lose energy to the surroundings, especially in cold weather. Energy is transferred from the warmer inside of the building to the colder outside.

Thermal insulation is used to slow this down.

Insulation does not completely stop energy transfer, but it reduces the rate at which energy is transferred. This means the building cools down more slowly and stays warmer for longer.

Examples of insulation include loft insulation, cavity wall insulation, double glazing, carpets and thick curtains.

These all help reduce unwanted energy transfers from the inside of the building to the outside.

What Is Thermal Conductivity?

Some materials are better at conducting energy than others.

Thermal conductivity tells us how well a material transfers energy by conduction.

You do not need to know the full definition for GCSE Physics, but you do need to know the idea:

A material with high thermal conductivity transfers energy quickly by conduction.

A material with low thermal conductivity transfers energy more slowly by conduction.

Metals usually have high thermal conductivity. This is why a metal spoon can quickly become hot when it is left in a hot drink.

Insulating materials, such as foam, wool and fibreglass, have low thermal conductivity. They are useful because they slow down energy transfer.

How Walls Affect the Rate of Cooling

The walls of a building affect how quickly the building cools down.

If the walls are made from a material with high thermal conductivity, energy is transferred through them quickly. This means the building loses heat faster and cools down more quickly.

If the walls are made from a material with low thermal conductivity, energy is transferred through them more slowly. This means the building loses heat more slowly and stays warmer for longer.

The thickness of the walls also matters.

Thicker walls reduce the rate of energy transfer because energy has to pass through more material. A building with thick, well-insulated walls will cool more slowly than a building with thin walls made from a material with high thermal conductivity.

The Key GCSE Idea

To reduce unwanted energy transfers, we try to slow down the transfer of energy to the surroundings.

Lubrication reduces friction between moving parts.

Thermal insulation reduces energy transfer by heating.

Materials with low thermal conductivity are good at reducing energy transfer by conduction.

Thicker walls and better insulation help buildings cool down more slowly.

This is why insulation is so important in homes. It reduces wasted energy, keeps buildings warmer and means less energy is needed to heat them.