How do mechanisms change the type, size or direction of movement?
The four types of motion, levers and linkages, rotary systems of gears, pulleys and belts, and cams and followers, with mechanical advantage and gear ratio.
A focused answer to the WJEC GCSE Design and Technology core technical principle on mechanical devices, covering the four types of motion, levers and linkages, gears, pulleys and belts, cams and followers, and how to calculate mechanical advantage and gear ratio.
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What this topic is asking
WJEC's core content includes mechanical devices that change movement. You need to know the four types of motion, the main mechanisms (levers, linkages, gears, pulleys, cams), and how to calculate mechanical advantage and gear ratio. This is core knowledge for Unit 1 across all three routes, and it is one of the few areas with calculations, so the maths is worth securing.
The four types of motion
Levers and linkages
A lever gives mechanical advantage when the effort is further from the pivot than the load:
A mechanical advantage greater than 1 means a small effort moves a large load.
Rotary systems: gears, pulleys and belts
The gear ratio tells you the change in speed and torque:
A ratio of 3:1 means the output turns three times slower with three times the torque.
Cams and followers
Try this
Q1. Name the four types of motion. [4 marks]
- Cue. Rotary, linear, reciprocating, oscillating.
Q2. A driver gear has 10 teeth and a driven gear has 40 teeth. State the gear ratio. [1 mark]
- Cue. , so 4:1.
Exam-style practice questions
Practice questions written in the style of WJEC exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
WJEC-style3 marksA driver gear has 20 teeth and the driven gear has 60 teeth. Calculate the gear ratio and describe its effect on speed and torque.Show worked answer →
A three mark calculation-and-explain question. Gear ratio is driven teeth over driver teeth: , so the ratio is 3:1 (1 mark). This means the driven gear turns three times slower than the driver (1 mark) but with more torque (turning force) (1 mark). Markers reward the correct ratio, the slower speed, and the gain in torque. A common error is to divide the wrong way (driver over driven) and conclude the gear speeds up.
WJEC-style4 marksDescribe two types of motion and give a product example of each.Show worked answer →
A four mark Describe question needing two motions, each with an example. For example: rotary motion is movement in a circle, as in a fan or a wheel (2 marks for the description plus example). Reciprocating motion is repeated backward and forward movement in a straight line, as in a sewing machine needle or a saw (2 marks). Other acceptable pairs use linear (straight line one way, as a conveyor belt) and oscillating (swinging back and forth about a pivot, as a pendulum or a swing). Markers reward a clear description and a correct example for each named motion.
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