Work & Energy Transfer
Work & Energy Transfer
- A force can transfer energy when it moves an object. Physics calls that transfer work done.
- Always name the force: “work done by the pulling force” and “work done by gravity” can have different values and signs.
First decide whether energy is transferred
moves
work doneno movement
no workforce ⟂ motion
no work| Situation | Work done by the named force |
|---|---|
| Push a crate and it moves forward | Positive: the force transfers energy to the crate |
| Push a wall and it does not move | Zero: there is no displacement |
| Hold a box while walking horizontally | Zero by the upward holding force: force and motion are perpendicular |
Feeling tired is not the physics test. Ask whether the object moves through a distance in the direction of the force.
Turn the idea into a calculation
Definition
1 markWhat is meant by work done by a force?
Model answer: The product of the force and the displacement in the direction of the force.
Symbols
- = work done (energy transferred) (J)
- = force (N)
- = displacement in the direction of the force (m)
- One joule is the work done when a force of 1 N moves its point of application 1 m in the force direction.
- Therefore . Work and energy have the same unit because work is an energy transfer.
- The equation assumes a constant force. For an angled force, the next lesson keeps only the component along the displacement.
Worked example
Start with force and motion in the same direction
A 25 N force pushes a box 4.0 m along a horizontal floor. Find the work done by this force.
- The force and displacement are parallel.
- .
Answer
Your turn9702/21/O/N/24 Q3(a)
State what is meant by the work done by a force. (9702/21/O/N/24 Q3(a))
Show worked answer
Worked answer: The product of the force and the displacement in the direction of the force.