# Heat energy

## Home learning focus

This lesson includes:

• one video showing the three ways heat energy can be transferred
• two activities

# Learn

In this short film heat transferred by conduction, convection and radiation are all explained.

## Heat energy

A hot object will never stay hot forever.

This is because it needs to reach thermal equilibrium.

It does this by transferring heat energy away from itself to a much cooler object.

There are three ways in which heat energy is transferred:

• conduction (if the objects are touching each other)
• convection

### Conduction

When a substance is heated, its particles gain internal energy and move more vigorously.

The particles bump into nearby particles and make them vibrate more.

This passes internal energy through the substance by conduction, from the hot end to the cold end.

Conduction is how pans work.

They can transfer heat from the hob to the food because they are made of metal, which is a good conductor of heat.

### Convection

The particles in liquids and gases can move from place to place.

Convection happens when particles with a lot of thermal energy in a liquid or gas move, and take the place of particles with less thermal energy.

When air is heated, it rises up and pushes down the cooler air beneath it. This cooler air then heats up and the cycle continues.

You can see this if you put your hand underneath a radiator. It will be much cooler than if you put it above the radiator.

All objects transfer energy to their surroundings by infrared radiation.

The hotter an object is, the more waves of infrared radiation it gives off.

Radiation doesn't involve particles, so it can transfer heat energy across empty space.

This is how the Sun transfers it heat through space, onto the Earth.

## Insulation

Insulation enables us to slow down or stop the transfer of heat energy, when we want to keep it in one place.

To do this we use insulators, which are poor conductors of heat.

### Keeping our homes warm

There are some simple ways to reduce heat energy transfers from a house:

• have carpets and curtains
• put reflective foil on the inside walls
• install double glazing

Double glazing involves having two panes of glass in the window instead of just one. There is air or an even better insulator such as argon gas between the two panes of glass. Gases are poor conductors of heat, so using them this way, reduces energy transfer by conduction.

Energy loss through walls can be reduced using cavity wall insulation. This involves blowing insulating material into the gap between the outside wall and the inside wall to reduce conduction. Loft insulation works in a similar way.

# Practise

There are lots of ways to try out your science skills.

## Activity 1

### Match and draw

Test your knowledge of insulation and methods of heat transfer with this match and draw downloadable worksheet from Beyond.