Work done in lifting loads
Lift boxes of different masses onto shelves at different heights, calculate the work done, and compare the power of quick and slow lifts.
Core concept
Work done = force × distance moved in the direction of the force; power = work ÷ time
Topic: Work, energy and power
In science, work is done when a force: A push or a pull. Forces can start, stop or turn things. All key words moves something in the direction of the force: work = force × distance, measured in joules (J). To lift a box at a steady speed: How far something travels in a certain time, like kilometres per hour. All key words you must push up with a force equal to its weight: The pull of gravity on something, measured in newtons. It is less on the Moon. All key words (mass: How much matter something has, measured in grams or kilograms. It is the same everywhere. All key words × g). So lifting a heavier box, or lifting it higher, takes more work. Power is how quickly work is done: power = work ÷ time, measured in watts (W). One watt is one joule per second.
What you will learn
- Calculate work done using work = force × distance.
- Show how mass and height affect the work done in lifting.
- Calculate power and explain why a quicker lift needs more power.
Before you start
- Know that weight = mass × g.
Materials
- Boxes of 1 kg, 2 kg, 5 kg and 10 kg
Equipment
- Shelves at 0.5 m, 1 m, 1.5 m and 2 m
- Metre rule and stopwatch
Procedure
- Lift the 2 kg box and the 10 kg box to the same height and record both.
- Lift one box to two different heights and record both.
- Lift the same box to the same height in 1 s and in 8 s and compare the power.
How this simulation is simplified
- g is taken as 10 N/kg.
- The box is lifted at a steady speed, so the lifting force equals its weight.