Work Done
Simple Explanation
In physics, work is done only when a force moves an object through a distance, in the direction of that force: W = Fd. Pushing hard against a wall that does not move does zero work, no matter how tired it makes you — because there is no distance moved.
Why Do We Need It?
Work is the bridge between force and energy: doing work on an object is exactly how energy gets transferred into (or out of) it, which is why work is measured in the same unit as energy, the joule.
Formula
Work Done
W = Fd
Work is done whenever a force moves an object through a distance in the direction of the force. No work is done if the object does not move, or if the force has no component in the direction of motion.
- W
- — work done, in joules (J)
- F
- — force applied, in newtons (N)
- d
- — distance moved in the direction of the force, in metres (m)
When to use it: Whenever the work done by a force moving an object through a known distance needs to be found.
Worked Example
Find the work done pushing a crate
A crate is pushed with a force of 150 N and moves 4 m in the direction of the force. Find the work done.
Why Does This Work?
Multiplying the force by the distance moved in its own direction gives exactly the total energy transferred by that force — which is the physical meaning of 'work done'.
Real-Life Example
Carrying groceries vs. lifting them
Carrying a heavy bag of groceries at a constant height across a flat room, versus lifting the same bag straight up onto a shelf.
Carrying the bag horizontally does no work against gravity (the weight force has no component in the direction of horizontal motion), while lifting it upward does real work against gravity, transferring energy into the bag's height.
Practice
A force of 80 N moves an object 3 m in the direction of the force. Find the work done.
EasyA person holds a heavy suitcase perfectly still in the air for one minute. How much work do they do on the suitcase?
MediumCommon mistake
Confusing everyday tiredness with physics 'work' — a force only does work if it actually moves something in its own direction; holding something still, no matter how effortful, does no work.
Quick Review
- W = Fd
- Work is only done if the object moves in the direction of the force.
- Work and energy share the same unit: the joule (J).