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This lesson brings together everything you have learned about mechanical devices and movement for AQA GCSE Design and Technology (8552), Section 3.1.5. It provides exam-style questions, model answers and revision strategies.
| Topic | What You Must Know |
|---|---|
| Types of motion | Linear, rotary, reciprocating, oscillating — definitions and examples |
| Input → Process → Output | Identify each stage in a mechanical system |
| Levers | Three classes; fulcrum, effort, load positions; MA calculation |
| Linkages | Reverse motion, parallel motion, bell crank, crank and slider |
| Gears | Simple, compound, worm, rack and pinion, bevel — gear ratio calculations |
| Cams | Pear, eccentric, snail, heart — profiles and displacement diagrams |
| Pulleys | Single fixed, single movable, block and tackle — MA calculations |
| Belt drives | Speed ratios, flat/V/toothed/crossed belts |
| Calculations | MA, VR, efficiency, gear ratios, output speed, torque |
Q: Name the type of motion exhibited by each of the following: (a) A car piston moving up and down in a cylinder. (b) A playground swing.
Model Answer: (a) Reciprocating motion — the piston moves back and forth along a straight line. (1 mark) (b) Oscillating motion — the swing moves back and forth along a curved arc around the pivot point. (1 mark)
Q: A pair of tweezers is used to pick up a small component. (a) Identify the class of lever used in tweezers. (1 mark) (b) Identify the position of the fulcrum, effort and load. (1 mark) (c) Explain why tweezers have a mechanical advantage of less than 1. (1 mark)
Model Answer: (a) Third class lever. (1) (b) The fulcrum is at the joined end, the effort is applied by the fingers in the middle, and the load is at the tips. (1) (c) Because the effort is applied between the fulcrum and the load, the effort arm is shorter than the load arm. This means the mechanism multiplies distance and precision rather than force, giving an MA less than 1. (1)
Q: A simple gear train consists of a driver gear with 12 teeth meshing with a driven gear with 48 teeth. The driver gear is connected to a motor running at 2400 RPM.
(a) Calculate the gear ratio. (1 mark) (b) Calculate the output speed. (1 mark) (c) State the effect on the output torque compared to the input. (1 mark) (d) State the direction of the output gear relative to the input gear. (1 mark)
Model Answer:
(a) GR=1248=4 (or 4:1) (1)
(b) Output speed=42400=600 RPM (1)
(c) The output torque is 4 times greater than the input torque (because the gear ratio is 4:1 and speed has decreased). (1)
(d) The output gear rotates in the opposite direction to the input gear (meshing spur gears rotate in opposite directions). (1)
Q: A displacement diagram shows a follower that rises gradually at a constant rate over most of the cam rotation, then drops suddenly back to its starting position.
(a) Name the type of cam that would produce this motion. (1 mark) (b) Give one real-world application for this type of cam. (1 mark) (c) Explain why a return spring is needed in most cam mechanisms. (1 mark)
Model Answer: (a) Snail cam (spiral cam). (1) (b) A music box — the snail cam gradually lifts a hammer, which then drops suddenly to strike a tuned metal tooth, producing a musical note. (1) (c) The spring keeps the follower in contact with the cam surface at all times, especially during the sudden drop, preventing the follower from bouncing off the cam. (1)
Q: A block and tackle pulley system is used to lift a crate weighing 800 N. The system has 4 rope sections supporting the load.
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