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1.7.2Motion, Forces and Energy

Work — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions

5 min read 8 parts Lesson 66 of 91 1 quiz

📚 Cambridge IGCSE Physics 0625 Hub / Topical Revision
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Lesson summary

1.7.2 Work — IGCSE PHYSICS notes: Understand that work done equals energy transferred and use W = Fd = ΔE.Work done = the energy transferred when a force moves an object (mechanical work) or when a current flows (electrical work).Equation (Extended) — W = Fd = ΔE.What the symbols…

  • What the symbols mean
  • Larger units
  • Lifting an object
  • Falling object
  • Gravitational potential energy
  • Kinetic energy

Part 1 of 6Work done and energy transfer

Work done
Work done the energy transferred when a force moves an object (mechanical work) or when a current flows (electrical work).
Equation (Extended)
  • W = Fd = ΔE.
    What the symbols mean: W = work done = energy transferred (J) · F = force (N) · d, s or x = distance moved in the direction of the force (m)
Unit
  • Unit the joule (J), where 1 J is the work done when a force of 1 N moves its point of application 1 m in the direction of the force.
Larger units
  • 1 kJ = 1000 J and 1 MJ = 1 000 000 J.

Part 2 of 6When no work is done

When no work is done
If the object does not move, no work is done.
If the movement is at right angles to the force, no work is done.
Carrying a bag horizontally at constant height does no work against gravity.

Part 3 of 6Where the energy goes

Work against friction transfers energy to the thermal store of the surfaces and heats them.
Lifting an object
  • Lifting an object work done = weight × height = mgh, which equals its gain in gravitational potential energy.
Falling object
  • Falling object gravitational potential energy changes to kinetic energy if air resistance is ignored.
Braking
  • Braking work done by the brakes equals the kinetic energy lost, F × d = ½mv².

Part 4 of 6Calculating work done

1
Identify the force acting.
2
Identify the distance moved in the direction of that force.
3
Convert to newtons and metres.
4
Multiply W = F × d.
5
State the answer in joules and which energy store it transfers to.

Part 5 of 6Related equations

QuantityEquationUnit
WorkW = F × dJ
Kinetic energyEk = ½mv²J
Gravitational potential energyEp = mghJ
PowerP = W ÷ tW
Efficiencyuseful output ÷ total input × 100%%

Part 6 of 6More from the specification

1
Mechanical work and vehicle speed
  • Mechanical work and vehicle speed accelerating a vehicle by performing work increases kinetic energy, providing a means to calculate final velocity.
2
Energy stores
  • Energy stores energy is held in stores such as kinetic, gravitational potential, thermal and chemical,
  • and is moved between them by work, heating or waves.
3
Work done
  • Work done work equals force multiplied by distance moved in the direction of the force, measured in joules.
4
Conservation of energy
  • Conservation of energy energy is never created or destroyed, so the total in a system stays constant.
5
Wasted energy
  • Wasted energy the part transferred to the surroundings by heating is not useful, and it lowers efficiency.
    • (for example from friction)
6
Energy stores
  • Energy stores energy is held in stores such as kinetic, gravitational potential, thermal and chemical,
    • and is moved between them by work, heating or waves.
7
Work done
  • Work done work equals force multiplied by distance moved in the direction of the force, measured in joules.
8
Conservation of energy
  • Conservation of energy energy is never created or destroyed, so the total in a system stays constant.
9
Wasted energy
  • Wasted energy the part transferred to the surroundings by heating is not useful, and it lowers efficiency.
    • (for example from friction)
10
Wasted energy
  • Energy transferred to stores that are not useful, usually thermal in the surroundings.
11
Gravitational field
  • Region where mass experiences gravitational force.
12
Transfer pathway
  • The way energy moves between stores, such as heating or work done.
13
Surroundings
  • Everything outside the system.

Key terms

TermMeaning
Work doneEnergy transferred by a force; W = F × d.
Joule1 J is the work done by 1 N moving an object 1 m.
Gravitational potential energyEnergy gained when lifted, Ep = mgh.
Kinetic energyEnergy of motion, Ek = ½mv².
Mechanical workEnergy transferred when a force moves an object.
Electrical workEnergy transferred when charge moves through a potential difference.

Avoid these mistakes

1
Using a force that is not in the direction of movement.
2
Saying work is done when an object does not move.
3
Using cm or kN without converting to m and N.
4
Confusing work in joules with power in watts.

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