What are the four types of motion, and how do mechanisms convert between them?
The four types of motion (linear, rotary, reciprocating, oscillating) and the role of mechanisms in changing the type, direction or magnitude of motion and force.
A CCEA A-Level Technology and Design answer on the four types of motion - linear, rotary, reciprocating and oscillating - and how mechanisms change the type, direction or magnitude of motion and force.
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What this dot point is asking
CCEA expects you to name and define the four types of motion (linear, rotary, reciprocating, oscillating) with examples, and to explain that a mechanism changes the type, direction or magnitude of motion or force. This is the foundation for levers, gears, pulleys and cams.
The answer
The four types of motion
What a mechanism does
Motion in the systems model
Worked example: tracing motion through a machine
Examples in context
Example 1. Car engine. The reciprocating motion of the pistons is converted to rotary motion at the crankshaft by the crank and connecting rod, a direct example of a mechanism changing the type of motion.
Example 2. Windscreen wiper. A motor's rotary motion is converted to the oscillating sweep of the wiper blade through a crank and linkage, showing rotary-to-oscillating conversion in an everyday product.
Try this
Q1. Name the four types of motion. [2 marks]
- Cue. Linear, rotary, reciprocating, oscillating.
Q2. What type of motion does an engine piston have? [1 mark]
- Cue. Reciprocating (back and forth in a straight line).
Q3. State three things a mechanism can change about motion or force. [3 marks]
- Cue. Its type, its direction and its magnitude.
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA 20196 marksName the four types of motion, giving an everyday example of each, and explain what a mechanism does.Show worked answer →
The four types of motion are:
- Linear: movement in a straight line in one direction. Example: a paternoster or a conveyor belt carrying an item along.
- Rotary: movement in a circle about a fixed axis. Example: a wheel, a fan or a drill chuck turning.
- Reciprocating: repeated backwards-and-forwards movement in a straight line. Example: a piston in an engine, or a sewing-machine needle.
- Oscillating: repeated swinging backwards and forwards along a curved path (about a pivot). Example: a pendulum or a swing.
A mechanism is a device that changes one type of motion into another, and/or changes the direction or magnitude of the motion or force. For example, a crank-and-slider converts rotary motion into reciprocating motion; gears change the speed and torque of rotary motion; a lever changes the size and direction of a force.
Markers reward all four motions correctly defined with sensible examples, and a clear statement that a mechanism changes the type, direction or magnitude of motion or force.
CCEA 20214 marksState the type of motion produced at the output of (a) a crank and slider driven by a rotating crank, and (b) the pendulum of a clock, and name the input motion in each case.Show worked answer →
(a) A crank and slider with a rotating crank: the input is rotary motion (the crank turning) and the output is reciprocating motion (the slider moving back and forth in a straight line), as in a piston engine or pump.
(b) A clock pendulum: it shows oscillating motion (swinging back and forth about a pivot along a curved path). It is driven/sustained by the escapement, but the pendulum's own motion is oscillating.
Markers want the correct input and output motions: rotary in, reciprocating out for the crank and slider; and oscillating for the pendulum.
Related dot points
- The three classes of lever, the principle of moments, mechanical advantage, and linkages (reverse-motion, bell-crank, parallel).
A CCEA A-Level Technology and Design answer on the three classes of lever, the principle of moments, calculating mechanical advantage and velocity ratio, and common linkages such as reverse-motion, bell-crank and parallel linkages.
- Spur, idler, compound, bevel and worm gears, the gear ratio, and the trade-off between speed and torque.
A CCEA A-Level Technology and Design answer on gear types - spur, idler, compound, bevel and worm - calculating the gear ratio from tooth numbers, and the trade-off between output speed and torque.
- Belt and pulley drives, the velocity ratio from pulley diameters, chain and sprocket drives, and pulley systems for lifting.
A CCEA A-Level Technology and Design answer on belt and pulley drives, calculating the velocity ratio from pulley diameters, chain and sprocket drives, and the mechanical advantage of pulley lifting systems.
- Cams and followers, cam profiles (pear, circular/eccentric, heart-shaped/snail), dwell, rise and fall, and crank-and-slider mechanisms.
A CCEA A-Level Technology and Design answer on cams and followers, common cam profiles (pear, circular/eccentric, heart-shaped), the meaning of dwell, rise and fall, follower types, and the crank-and-slider mechanism for rotary-to-reciprocating conversion.
- Pneumatic components: single- and double-acting cylinders, control valves (3/2 and 5/2), and calculating the thrust of a cylinder.
A CCEA A-Level Technology and Design answer on pneumatic systems, single- and double-acting cylinders, 3/2 and 5/2 control valves, and calculating the output force (thrust) of a cylinder from air pressure and piston area.
Sources & how we know this
- CCEA GCE Technology and Design specification — CCEA (2016)