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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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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?

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    Total kinetic and potential energy of the particles

  3. 3

    What is the link between temperature and particle energy?

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    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.

Practice questions

Have a go at each one before you open its answer.

  1. Question 1 Explain 3 marks

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

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    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.

    Mark scheme

    • Work is done on the gas — 1 mark
    • Internal energy of the gas increases — 1 mark
    • Temperature rises — 1 mark
  2. Question 2 State 2 marks

    What is meant by work done?

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    Model answer

    The transfer of energy by a force.

    Mark scheme

    • Transfer of energy — 1 mark
    • By a force — 1 mark
  3. Question 3 Explain 4 marks

    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.

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    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.

    Mark scheme

    • 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
  4. Question 4 Explain 2 marks

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

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    Model answer

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

    Mark scheme

    • Energy transferred to the surroundings — 1 mark
    • Internal energy or temperature decreases — 1 mark
  5. Question 5 Describe 3 marks

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

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    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.

    Mark scheme

    • 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

Quick check

  1. Work done on a gas increases its...

    1. Amass
    2. Bvolume only
    3. Cinternal energy
    4. Ddensity only
    Show answerHide answer

    C: internal energy

    Energy is transferred to the gas.

  2. Compressing a gas quickly makes its temperature...

    1. Afall
    2. Bstay the same
    3. Cbecome zero
    4. Drise
    Show answerHide answer

    D: rise

    Its internal energy rises.

  3. Work is the transfer of energy by a...

    1. Aforce
    2. Bcurrent
    3. Ctemperature
    4. Dwave
    Show answerHide answer

    A: force

    Force times distance.

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

    1. Atyre only
    2. Bair
    3. Chandle only
    4. Dspring
    Show answerHide answer

    B: air

    The air is compressed.

  5. Temperature rise means the particles' average...

    1. Amass increases
    2. Bsize increases
    3. Ckinetic energy increases
    4. Dcharge increases
    Show answerHide answer

    C: kinetic energy increases

    Faster molecules.

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