Lifting Machines on the Job – Work, Power, Efficiency
PhysicsEnergy & MomentumAges 15–16
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Energy & Momentum
A construction-site crane, a farm hoist, or a passenger lift raises a load to height h. Adjust the mass, height, lifting speed, and friction loss to see the useful work A = mgh, the total work, the power P = F·v, and the machine's efficiency — the very quantities an operator must calculate when choosing a machine.
Lesson: Physics in Occupations
What it shows
Lifting a load of mass m through a height h takes useful work A = mgh, which depends only on the load and the height, not on how quickly the load is raised. Power is the rate of doing work, P = A/t = F·v, so lifting the same load twice as fast needs twice the power. Real machines lose energy to friction in pulleys, cables and gearboxes, so the motor must supply more total work than the useful work. Efficiency is the ratio of useful work to total work, and it is always less than 100%.
How to use
Choose a Machine type, set Load mass and Lift height, and press Test lift to watch the load rise while the energy bar splits into useful and lost parts. Then change one quantity at a time: raise Lift speed and compare what happens to the work and to the power, or increase Friction loss and see how the total work and the efficiency respond. Students can check each readout against their own calculation.
Parameters you can change
- Machine type Construction crane, Farm produce hoist, Passenger lift
- Load mass 50–3000 kg
- Lift height 2–40 m
- Lift speed 0.2–3 m/s
- Friction loss 0–45 %
Questions to explore
- If the load is lifted twice as fast, what happens to the useful work and to the power?
- Why is the efficiency of a real lifting machine always less than 100%?
- How much total work must the motor do to lift 500 kg through 12 m with a 20% friction loss?
