### KS3 Physics

Motion and Forces
Waves
Matter

# Conduction and Convection

We will cover conduction and convection together, as both of these methods of energy transfer require particles, unlike radiation.

## Conduction

Both conduction and convection are methods of energy transfer that require particles. However, conduction is the primary method of energy transfer in solids.

When a substance is heated, its particles vibrate more vigorously and begin to bump into each other. This eventually causes all of the particles to vibrate more vigorously. When this happens, energy transfers along the substance via conduction.

The diagram below represents the arrangement of atoms in a solid and the colour represents how hot each atom is.

• The more red the atom is, the more heat energy the atom has
• The more blue the atom is, the less heat energy the atom has

As the atoms start to vibrate more, they collide with neighbouring atoms, transferring heat energy.

For example, when a metal spoon is placed into a hot drink, the whole spoon ends up becoming hot.

### Conductors and insulators

If a material is a good conductor, then it is a poor insulator, and vice versa. This is because conductors transfer heat easily and insulators do not transfer heat easily.

#### Good conductors/poor insulators

An example of a good conductor is metal.

When heat passes through a substance, it has to pass from particle to particle. Solids are usually the best conductors because their atoms are very close together. This means that when the atoms vibrate, they instantly collide with neighbouring particles.

Some examples of good insulators include:

• Plastic
• Air
• Wood
• Rubber

Good insulators are typically poor conductors because their particles are more spaced out. Therefore, it is more difficult to transfer energy to neighbouring particles because they are further away.

## Convection

Convection happens in liquids and gases, in which the particles are far apart and are free to move randomly. Although the particles in liquids are closer together than gases, they are still able to move and flow.

Close to the heat source, particles gain thermal energy, causing them to vibrate and move more quickly. This leads to the particles moving further apart, making the liquid or gas less dense.

It’s important to note that individual particles don’t become less dense. Instead, the overall density of the gas or liquid decreases.

1. The moving particles with a lot of thermal energy rise and transfer energy to the particles at the top, replacing the particles with little thermal energy.

2. Particles at the top, which as a whole are cooler and denser, fall to take the place of the high-energy particles.

This constant movement of particles is known as a convection current, where particles rise and fall, transferring energy to cooler regions.

Let’s examine a practical example: heating water in a pot.

1. The pot is heated from the bottom.

2. The particles at the bottom of the pan start to vibrate more as they are heated.

3. These particles then transfer heat energy to other areas of the pan and to the water molecules at the bottom of the pan.

4. The water inside the pan is being heated using convection, which is why convection currents start to form.