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Types of Energy

Unit 2: Energy and Our Universe

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Heat energy only flows when there is a temperature difference between a warmer area and a cooler area.

What is thermal energy?

Heat is a type of energy called thermal energy.

conduction,

During heat transfer, thermal energy always moves in the same direction:

convection and radiation.

Heat can be transferred (moved) by three main processes:

What happens to hot cup of tea in a cool room?

What happens to a cold ice lolly on a warm day?

What do these examples tell you about heat transfer?

HOT COLD

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What is conduction?

When you touch something hot, the heat is transferred to your hand by conduction.

Conduction is the transfer of heat energy between neighbouring particles by their vibration.

Would you expect conduction to be most effective in solids, liquids or gases?

Is conduction more effective in metals or plastics?

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Where is conduction most effective?

solid liquid gas

Conduction is more effective in solids than liquids or gases due to the arrangement of particles. In solids, they are very close together and ordered and so easily transmit energy from one to another by vibration.

Metals are better conductors than plastics because they have free electrons that move through the metal, transferring the thermal energy.

free electron

metal ion

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What is convection?

The warmer regions will rise because they are less dense.

The cooler regions will sink as they are more dense.

This is how heat transfer takes place in fluids and is called convection.

Liquids and gases can both flow and behave in similar ways, so they are called fluids.

When fluids are heated, the particles move around more and spread out. Warmer regions of a fluid are therefore less dense than cooler regions.

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Convection currents

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Case study: the radiator

Confusingly, radiators mainly transfer heat by convection, although they do also transfer some heat by radiation.

Warm air from the radiator rises, setting up a convection current in the room.

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infraredwaves

The Earth is warmed by heat energy from the Sun. How does this heat energy travel from the Sun to the Earth?

There are no particles between the Sun and the Earth, so the heat cannot travel by conduction or by convection.

The heat travels to Earth by infrared waves. These are similar to light waves and are able to travel through empty space.

What is thermal radiation?

Infrared waves heat up objects that absorb them, and are alsoknown as thermal radiation.

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Investigating thermal emission

Which type of kettle would cool down faster: a black kettle or a shiny metallic kettle?

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Case study: the vacuum flask

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Thermal energy: summary