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How do mechanisms change the type, direction or size of motion and force?

The four types of motion, mechanisms that change motion (levers, linkages, gears, pulleys, cams, cranks) and how they alter direction, speed and force.

A focused answer to AQA GCSE Engineering on the four types of motion and the mechanisms (levers, linkages, gears, pulleys, cams and cranks) that change the type, direction, speed or force of motion.

Generated by Claude Opus 4.89 min answerUpdated 2026-06-02

Reviewed by: AI editorial process; not yet individually human-reviewed

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What this dot point is asking
The four types of motion
Mechanisms that change motion
Gear ratios
Try this

What this dot point is asking

AQA wants you to name the four types of motion, recognise the common mechanisms, and explain how each changes the type, direction, speed or force of motion, including simple gear ratio calculations. Gear questions that ask for a ratio and an output speed are common, so be ready to calculate.

The four types of motion

Mechanisms that change motion

Levers: change the size and direction of a force about a pivot (fulcrum), giving mechanical advantage.
Linkages: join levers to change the direction or type of motion (a reverse-motion linkage flips direction).
Gears: meshing toothed wheels change rotary speed and torque; an idler gear between two gears changes the direction of rotation without changing the ratio.
Pulleys and belts: transfer rotary motion between shafts and change speed by the ratio of their diameters.
Cams and followers: change rotary motion into reciprocating (up-and-down) motion, the shape of the cam setting the movement.
Cranks and sliders: change rotary motion into reciprocating motion and back, as in a car engine.

Gear ratios

For a driver of $20$ teeth and a driven of $60$ teeth, the ratio is $60/20 = 3$ , so the output turns three times slower with about three times the torque. Gears always trade speed against turning force, which is the central idea examined. The same trade-off applies to a pulley-and-belt drive, where the ratio is set by the diameters of the two pulleys rather than teeth: a small driver pulley turning a large driven pulley gears down (slower, more torque), while a large driver turning a small driven gears up (faster, less torque). A compound gear train uses two or more pairs in series to reach a large overall ratio in a small space, the overall ratio being the product of the individual ratios.

Worked example: gearing down a motor to drive a conveyor

A motor runs at $1200 \text{ rev/min}$ and drives a conveyor roller through a gear pair: a $16$ -tooth driver on the motor and a $64$ -tooth gear on the roller. Find the gear ratio, the roller speed and the effect on torque.

step Calculate the gear ratio

Gear ratio $= \dfrac{\text{driven teeth}}{\text{driver teeth}} = \dfrac{64}{16} = 4$ , so $4:1$ .

step Calculate the output speed

Output speed $= \dfrac{\text{input speed}}{\text{gear ratio}} = \dfrac{1200}{4} = 300 \text{ rev/min}$ . The roller turns four times slower than the motor.

step Find the effect on torque

Because gears trade speed for force, gearing down by $4:1$ increases the torque at the roller by about four times (ignoring friction losses).

step Interpret for the conveyor

The motor spins fast with little torque; the gear train turns this into a slower, more powerful rotation that can move a loaded belt. This is why machines use gear-down trains: to convert a fast, weak motor output into the slower, stronger motion the load needs.

Try this

Q1. Name the type of motion of a swinging pendulum. [1 mark]

Cue. Oscillating.

Q2. A driver gear of $15$ teeth drives a $45$ -tooth gear. State the gear ratio. [1 mark]

Cue. $45/15 = 3$ , so $3:1$ .

Exam-style practice questions

Practice questions written in the style of AQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

AQA 20184 marksA gear train has a driver gear with

20

teeth meshing with a driven gear of

60

teeth. Calculate the gear ratio and explain its effect on speed and torque.

Show worked answer →

A good answer calculates the ratio and links it to speed and torque.

The gear ratio is driven teeth divided by driver teeth: $60 / 20 = 3$ , so a ratio of $3:1$ .

This means the driver turns three times for each turn of the driven gear, so the driven gear turns at one third of the speed. Because the gears trade speed for force, the torque (turning force) at the driven gear is increased about three times.

Markers reward the correct ratio calculation and the link that a higher ratio reduces output speed but increases torque.

AQA 20216 marksA driver gear of

15

teeth turning at

300 \text{ rev/min}

drives a gear of

45

teeth. Calculate the gear ratio and the output speed, and explain how this gear train would be used in a hand-cranked winch.

Show worked answer →

A good answer finds the ratio, applies it to the speed, and links the effect to the winch.

Gear ratio $= \dfrac{\text{driven teeth}}{\text{driver teeth}} = \dfrac{45}{15} = 3$ , so $3:1$ .

Output speed $= \dfrac{\text{input speed}}{\text{gear ratio}} = \dfrac{300}{3} = 100 \text{ rev/min}$ .

In a winch, this gear-down trades speed for torque: the output turns three times slower than the input but with about three times the turning force, so a person can wind a heavy load by hand more easily, at the cost of turning the handle more times.

Markers reward the ratio of $3:1$ , the output speed of $100 \text{ rev/min}$ , and the explanation that gearing down increases torque to lift the load.

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Sources & how we know this

AQA GCSE Engineering (8852) specification — AQA (2017)