Simple machines · Year 6
Simple machines such as levers, pulleys, gears, ramps and wheels-and-axles make jobs easier by changing the size or direction of a force. A machine that lets you use a smaller force always makes you move further, so you never get more work out than you put in.
Key facts
- The six simple machines: lever, pulley, wheel and axle, inclined plane (ramp), wedge, screw.
- Mechanical advantage (MA) = load ÷ effort.
- Lever: effort × distance from pivot = load × distance from pivot.
- A pulley system with n supporting ropes: effort = load ÷ n (ideally), but you pull n times as much rope.
- Gears: the gear with fewer teeth turns faster; meshing gears turn in opposite directions.
- Ramp (no friction): effort × length = load × height. Efficiency = useful work out ÷ work in.
Worked examples
Example 1
A pulley system with 4 supporting ropes lifts a 1,200 N load by 1.5 m. Find the effort and how much rope is pulled.
Answer: 300 N; 6 m