Gear-driven and belt-driven systems transmit continuous rotary motion, whereas cam systems, levers, and linkages transmit or transform motion and force in different ways. The key differences are their components, input-output motion, mechanical advantage, and suitability for particular tasks.
In A3.3 Introduction to mechanical systems, a mechanical system has an input, a process that transmits or transforms motion, and an output.
| System | Mechanism and motion | Typical application |
|---|---|---|
| Gear-driven | Meshing toothed wheels transmit rotary motion without slipping. Gear size can change speed, torque, and direction. | Bicycle gearing, clocks, gearboxes |
| Belt-driven | A flexible belt transfers rotary motion between pulleys. It can connect shafts over greater distances but may slip. | Conveyor belts, washing machines |
| Cam | A shaped rotating cam pushes a follower, usually converting rotary motion into reciprocating or oscillating motion. | Engine valves, automated toys |
| Lever | A rigid bar rotates around a fulcrum. The positions of the effort, load, and fulcrum determine the lever class and mechanical advantage. | Scissors, wheelbarrows, tweezers |
| Linkage | Connected rigid members and pivots transmit or transform motion between an input and output. | Windscreen wipers, folding mechanisms |
For gears, the speed ratio depends on the number of teeth:
A small driving gear turning a larger driven gear reduces output speed but increases output torque. Belt systems achieve a similar effect through pulley diameters, although slipping makes the transmission less precise.
A common misconception is that cams and linkages simply transmit rotary motion. A cam normally creates a repeating output determined by its profile, while a linkage can transform motion in several ways depending on the geometry and pivot positions.
Exam technique: For an IB comparison, identify the input and output motion, explain how force or speed changes, and justify the mechanism for a stated design context. Do not merely list example products.
