Cam & Crank Mechanisms
Convert rotary to reciprocating motion
Converting Motion
Mechanisms convert one type of motion to another. A cam converts rotary motion to reciprocating (up-and-down) motion — like the engine valves in a car. A crank converts rotary to reciprocating (or vice versa) — like bicycle pedals converting your leg push into wheel rotation.
Example
Cam and Crank Systems
Cam mechanism:
A shaped disc (cam) rotates on a shaft
A follower rests on the cam surface
As the cam rotates, the follower moves up and down
Cam shape determines the motion pattern
Crank mechanism:
Rotating disc + connecting rod + slider
Rotation → back-and-forth motion
Examples: car engine (both!), sewing machine, windscreen wipers
Note
Remember
Cams can create complex motion patterns — the shape of the cam determines how the follower moves. A round cam = smooth motion. An egg-shaped cam = pause at top. Cranks are simpler but only create sinusoidal (smooth wave) motion. Both are everywhere in machines around us.
Key Vocabulary
CamA shaped disc that converts rotary to up-and-down motion
CrankA mechanism converting rotary to reciprocating motion
ReciprocatingMotion that goes back and forth in a straight line
Rotary motionMotion that goes round and round (circular)
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