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Physics · Particle model of matter

Increasing the pressure of a gas

Explain how doing work on a gas increases its internal energy and temperature, for example in a bicycle pump (Higher tier only).

  • Higher
  • 6 key terms
  • All boards
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Teacher resources

The teacher copies: slides with the questions built in, the answers, and anything else attached to this lesson for whoever is teaching it.

Student handouts

The same files the students see, to print or hand out.

Warm-up

Answer each one, then check.

  1. 1

    What is work done?

    Show answerHide answer

    Energy transferred by a force

  2. 2

    What is internal energy?

    Show answerHide answer

    Total kinetic and potential energy of the particles

  3. 3

    What is the link between temperature and particle energy?

    Show answerHide answer

    Higher temperature means more kinetic energy

  4. 4

    What happens to gas pressure when volume decreases?

    Show answerHide answer

    It increases

  5. 5

    What is a force?

    Show answerHide answer

    A push or a pull

Learning Objectives

  1. 1Define work as the transfer of energy by a force.
  2. 2Explain that doing work on a gas increases its internal energy.
  3. 3Explain why the temperature of a gas rises when it is compressed, for example in a bicycle pump.

WORK ON A GAS (HIGHER TIER)

Work is the transfer of energy by a force. Doing work on a gas increases the internal energy of the gas and can cause its temperature to rise.

This is why a bicycle pump gets warm when used.

Why the Gas Warms

A chain of ideas.

  1. 1 Push the piston

    You apply a force that moves the piston: work is done on the gas.
  2. 2 Energy transferred

    The energy is transferred to the gas particles.
  3. 3 Kinetic energy increases

    The particles move faster.
  4. 4 Temperature rises

    The average kinetic energy of the gas increases.

Bicycle Pump

Explain why the barrel of a bicycle pump gets hot when the pump is used to inflate a tyre.

Show the solutionHide the solution
  1. 1 Work done The force on the piston does work on the air inside
  2. 2 Internal energy The internal energy of the air increases as the energy is transferred to its molecules
  3. 3 Temperature The temperature of the air rises, and thermal energy is transferred to the barrel

AnswerWork is done on the air, increasing its internal energy and temperature, which warms the pump.

Exam Points

How to score the marks.

  • Say 'work is done'

    Name the force and the energy transfer.

  • Link to internal energy

    Increase in internal energy of the gas.

  • Link to temperature

    Average kinetic energy of the molecules increases, so temperature rises.

Warm Pump

You pump up a tyre and the base of the pump gets warm. Explain why using the ideas of work and internal energy.

1. Say what is being done to the gas.

2. Link to temperature.

A good answer shows: Work is done on the air by the force pushing the piston. This increases the internal energy of the air (kinetic energy of the molecules), so the temperature increases and the pump warms.

Can I...?

  1. 1Define work.
  2. 2Explain work on a gas.
  3. 3Link work to internal energy.
  4. 4Link internal energy to temperature.
  5. 5Use the bicycle pump example.
  6. 6Write a clear chain of reasoning.
  7. 7Use the correct terms.
  8. 8Explain warming.

Summary & Exam Focus

  • Work is energy transferred by a force.
  • Work done on a gas increases its internal energy.
  • The temperature of the gas increases.
  • Example: a bicycle pump.

Exam focus

Explain why the air in a bicycle pump gets hotter when the pump is used. (3 marks) (3 marks)

Work is done; internal energy rises; temperature rises.

Key terms

The vocabulary this lesson expects you to use. Each one is linked from the first place it appears above.

Work
Energy transferred by a force.
Internal energy
Total kinetic and potential energy of particles.
Compression
Squashing a gas into a smaller volume.
Molecule
A group of atoms bonded together.
Enclosed gas
A gas trapped in a container.
Temperature
A measure of average kinetic energy.

Questions and answers

10 questions set on this lesson, with the mark schemes and model answers open.

1. Exam question Explain 3 marks Easier

A student uses a bicycle pump to inflate a tyre and notices that the pump becomes warm. Explain why.

Mark scheme — 3 marks available

  • Work is done on the gas — 1 mark
  • Internal energy of the gas increases — 1 mark
  • Temperature rises — 1 mark

Model answer

Work is done on the air by the force on the piston. This transfers energy to the air, so the internal energy of the air increases and the temperature rises, warming the pump.

2. Exam question State 2 marks Easier

What is meant by work done?

Mark scheme — 2 marks available

  • Transfer of energy — 1 mark
  • By a force — 1 mark

Model answer

The transfer of energy by a force.

3. Exam question Explain 4 marks Easier

A gas in a sealed syringe is compressed quickly by pushing in the plunger. Explain, using the particle model, why the temperature of the gas rises.

Mark scheme — 4 marks available

  • Work is done on the gas — 1 mark
  • Energy transferred to the particles — 1 mark
  • Average kinetic energy increases — 1 mark
  • So the temperature rises — 1 mark

Model answer

The force on the plunger does work on the gas. Energy is transferred to the gas particles, so the average kinetic energy of the particles increases. The temperature of the gas depends on the average kinetic energy, so the temperature rises.

4. Exam question Explain 2 marks Easier

Explain why a gas compressed slowly and allowed to cool would not stay hot.

Mark scheme — 2 marks available

  • Energy transferred to the surroundings — 1 mark
  • Internal energy or temperature decreases — 1 mark

Model answer

The energy is transferred by heating to the surroundings, so the internal energy and temperature of the gas decrease.

5. Exam question Describe 3 marks Easier

Describe the energy changes when a gas is compressed by a piston and then allowed to expand pushing the piston out.

Mark scheme — 3 marks available

  • Work done on the gas: internal energy increases — 1 mark
  • Gas does work on the piston when expanding — 1 mark
  • Internal energy decreases — 1 mark

Model answer

When compressed, work is done on the gas so its internal energy increases. When it expands and does work on the piston, its internal energy decreases and it cools.

6. Multiple choice 1 mark Easier

Work done on a gas increases its...

  1. A mass
  2. B volume only
  3. C internal energy Correct
  4. D density only

Why: Energy is transferred to the gas.

7. Multiple choice 1 mark Core

Compressing a gas quickly makes its temperature...

  1. A fall
  2. B stay the same
  3. C become zero
  4. D rise Correct

Why: Its internal energy rises.

8. Multiple choice 1 mark Core

Work is the transfer of energy by a...

  1. A force Correct
  2. B current
  3. C temperature
  4. D wave

Why: Force times distance.

9. Multiple choice 1 mark Core

A bicycle pump warms up because work is done on the...

  1. A tyre only
  2. B air Correct
  3. C handle only
  4. D spring

Why: The air is compressed.

10. Multiple choice 1 mark Stretch

Temperature rise means the particles' average...

  1. A mass increases
  2. B size increases
  3. C kinetic energy increases Correct
  4. D charge increases

Why: Faster molecules.