Notes
In science, work is done when a force moves an object in the direction of the force.
- $W = Fd$. Units: joules (J); 1 J = 1 N·m.
- Example: Pushing a box with 20 N over 5 m does $20 \times 5 = 100$ J of work.
- No movement means no work: holding a heavy box still, or pushing on a wall that does not move, is zero work.
- A force at right angles to the motion does no work: carrying a bag while walking level.
Practice
How much work is done lifting a box with a force of 30 N through 4 m?
$W = Fd = 30 \times 4 = 120$ J.
A student pushes on a wall with 200 N, but the wall does not move. How much work is done on the wall?
No distance, so $W = 200 \times 0 = 0$.
What is the SI unit of work?
1 joule equals 1 newton-meter.
Ready for more? Take the Unit 8 test.