Work is energy transferred
A force does work when it causes movement through a distance. Work done and energy transferred are both measured in joules.
W = Fs
Force F is in newtons; distance s is in metres along the direction of the force.
Lesson 1.6 · AQA Combined Science
Work done and power
Worked example: work
A 20 N force moves a box 3 m along the force.
W = 20 × 3 = 60 J
If there is no movement, this force does no mechanical work on the object, even if holding it makes your muscles tired.
Power: how quickly
P = Et = Wt
Power is the rate of energy transfer or work done. 1 watt = 1 joule per second.
Two motors do the same work. The one taking less time has greater power.
Worked example: power
A motor transfers 600 J in 3 seconds.
P = 6003 = 200 W
Use seconds, not minutes. 1 kW = 1000 W.
Rearrange to find energy: E = Pt. To find time: t = E / P.
Remember
W = Fs; P = E/t. Work and energy are in J; power is in W. Greater power means a faster transfer.
20 quick questions
Try it
Build confidence with pictures, clues and instant feedback.
Question 1 of 20Spot · Match · Explain
Use the pictures to help you.
Read the numbers
How many particles?
Case closed!
One point for each answer you get right first time.
No timer. Take your time and use a clue whenever you need one.