Simple machines – pulleys, inclined plane, wheel and axle, screw jack and gears
PhysicsEnergy & MomentumAges 15–16Virtual lab
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A virtual bench for simple machines: fixed and movable pulleys, a block and tackle, an inclined plane, a wheel and axle, a screw jack and a gear winch. Set the load, the friction and the pulley mass, pull with a spring balance and measure how far the effort and the load move. The simulation works out mechanical advantage, velocity ratio and efficiency, and a work bar shows that work output never exceeds work input.
Lesson: Simple machines: mechanical advantage, velocity ratio and efficiency
What it shows
A simple machine lets a small effort E lift a large load L. The mechanical advantage MA = L/E compares the forces, while the velocity ratio VR = dE/dL compares the distances moved and depends only on the geometry. Efficiency is MA/VR, the useful work L·dL divided by the work input E·dE. Friction in pulleys, bearings and screw threads, and lifting the lower pulley block, waste energy, so work output is always less than work input. Ropes are treated as light and unstretchable, and each pulley, bearing or gear mesh loses a fixed fraction of the force. Levers are covered in the simulation Levers and moment of force.
How to use
Choose a machine tab, set Load mass m and the friction, then press Pull (Turn handle for the screw jack and the gear winch). Read the spring balance and the two rules: each lift adds a row with L, E, dL, dE, MA, VR and efficiency. For pulleys, change Supporting strands n and Mass of each moving pulley, then raise the load to see on the graph how efficiency changes.
Parameters you can change
- Machine Pulleys, Inclined plane, Wheel and axle, Screw jack, Gear winch
- Pulley system Fixed pulley, Movable pulley, Block and tackle
- Supporting strands of the block and tackle 2–6
- Load mass 1–100 kg
- Mass of each moving pulley 0–2 kg
- Friction loss per pulley, bearing or gear mesh 0–15 %
- Slope angle 5–60 °
- Coefficient of friction (incline, screw thread) 0–0.6
- Wheel radius 10–60 cm
- Axle radius 2–20 cm
- Screw pitch 2–12 mm
- Handle or crank length 10–60 cm
- Teeth on the pinion 8–40
- Teeth on the large gear 12–96
Questions to explore
- Why is a block and tackle more efficient with a heavy load than with a light one?
- How does the velocity ratio of an inclined plane change when the slope becomes steeper?
- Why can no real machine have an efficiency of 100 %?
