What does the Mechanisms and motion topic cover in CCEA GCSE Technology and Design?

It covers the four types of motion (linear, rotary, reciprocating and oscillating), levers and linkages with the three classes of lever and the principle of moments, mechanical advantage, gears and gear trains with gear-ratio calculations, belt and chain drives with velocity-ratio calculations, and motion converters such as cams and followers, the crank and slider, rack and pinion and screw threads. Calculations of gear ratio, velocity ratio, moments and mechanical advantage are common in the exam.

How do you calculate a gear ratio?

The gear ratio of a simple gear train is the number of teeth on the driven gear divided by the number of teeth on the driver gear. A ratio of 3:1 means the driver turns three times for every one turn of the driven gear, so the output is three times slower with three times the torque. Output speed is the input speed divided by the gear ratio. The same idea gives the velocity ratio of a belt or chain drive using pulley diameters or sprocket teeth.

What is the principle of moments?

A moment is the turning effect of a force, equal to the force multiplied by the perpendicular distance from the pivot, measured in newton metres. A lever is balanced when the total clockwise moment equals the total anticlockwise moment, which lets you find an unknown force or distance. Mechanical advantage is the load divided by the effort, and a longer effort arm gives a greater mechanical advantage.

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Mechanisms and motion: study guide - CCEA GCSE Technology and Design

A study guide to the Mechanisms and motion topic of CCEA GCSE Technology and Design: the four types of motion, levers and the principle of moments, mechanical advantage, gears and gear trains, belt and chain drives, and motion converters such as cams, cranks, rack and pinion and screw threads.

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What this topic covers
How it is examined
Key formulae to recall
How to revise it

Mechanisms and motion is the part of Unit 1 with real calculations: gear ratios, velocity ratios, moments and mechanical advantage. It is also where the mechanical option in Unit 2 builds from.

What this topic covers

Types of motion - linear, rotary, reciprocating and oscillating, and how mechanisms convert one to another.
Levers and linkages - the three classes, the principle of moments, mechanical advantage, and linkages.
Gears and gear trains - gear ratio, speed and torque, idler gears and compound trains.
Belt and chain drives - velocity ratio, slip, and choosing between them.
Cams, cranks and converters - cam and follower, crank and slider, rack and pinion and screw threads.

How it is examined

Expect to name the types of motion and the lever classes, calculate moments and mechanical advantage, calculate gear ratios and velocity ratios and the resulting output speed, explain the idler gear and compound trains, compare belts and chains, and state the input and output motion of each converter. Show your working - method marks are awarded.

Key formulae to recall

Moment: $\text{moment} = \text{force} \times \text{distance from the pivot}$ (N m).
Balance: clockwise moment $=$ anticlockwise moment, $F_1 d_1 = F_2 d_2$ .
Mechanical advantage: $\text{MA} = \dfrac{\text{load}}{\text{effort}}$ .
Gear ratio: $\dfrac{\text{driven teeth}}{\text{driver teeth}}$ ; velocity ratio: $\dfrac{\text{driven diameter}}{\text{driver diameter}}$ .
Output speed: $\dfrac{\text{input speed}}{\text{gear or velocity ratio}}$ .

How to revise it

Learn the motion vocabulary. Name each type and a converter for each conversion.
Drill the calculations. Practise gear ratio, velocity ratio, moments and mechanical advantage until they are automatic.
Remember driven over driver. Both gear ratio and velocity ratio are driven divided by driver.
Master the speed-torque trade-off. A reduction is slower with more torque; an increase is faster with less.
Match converters to motion. For each mechanism state the input and output motion and a real use.

Sources & how we know this

CCEA GCSE Technology and Design specification — CCEA (2017)