Work Done & Energy Transfer (AQA GCSE Physics Combined Science): Revision Notes
Work and energy
What is work done?
Work is done when you apply a force to move something through a distance. The amount of work done equals the amount of energy that gets transferred.
When you push or pull an object and it moves, you are doing work on that object. However, if the object doesn't move (even if you push really hard), then no work is done.
Key point: Work is only done when there is movement in the direction of the force.
The work done formula
You can calculate work done using this simple formula:
Or written as:
Where:
- = work done (measured in joules, J)
- = force (measured in newtons, N)
- = distance moved (measured in metres, m)
Remember: 1 joule = 1 newton-metre
This relationship shows that the joule is a derived unit, combining force and distance measurements.
Work done when moving objects horizontally
When you push or pull something across a flat surface, you're doing work against friction.
Worked Example: Pushing Against Friction
If you push a car with a force of 100N for a distance of 3m, the work done is:
Work done =
Important effect: When work is done against friction, the object heats up. The more friction you work against, the more the temperature rises.
Work done when lifting objects
When you lift something up, you're doing work against gravity. This increases the object's gravitational potential energy.
The work done when lifting can be calculated using:
- (where is the lifting force and is the height)
- Or (where is mass, is gravity, is height)
Both formulas give the same result because the lifting force equals the object's weight () when lifting at constant speed.
Worked Example: Lifting Against Gravity
Lifting a 20kg mass through 15m:
Work done =
Practice calculations
Here are some typical exam-style questions:
Worked Example 1: Horizontal Force
A force of 350N pushes an object 90m along the ground.
Solution: Work done =
Worked Example 2: Finding Force
How much force is needed to do 360,000J of work over 300m?
Solution:
- Rearrange to get
- Force =
Worked Example 3: Lifting Calculation
A 25kg mass is lifted 40m vertically.
Solution: Work done =
Key Points to Remember:
- Work done equals energy transferred
- Use the formula:
- Work is measured in joules (J)
- Work is only done when something moves in the direction of the force
- Lifting objects increases their gravitational potential energy
- Working against friction causes objects to heat up