Linkages, Rotary Systems and Gear Ratios
How mechanisms pass on and change motion: linkages that change direction, cams that make an up-and-down movement, gears and pulleys that transfer turning motion, and how to work out a gear ratio.
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Passing on motion
Mechanical devices pass on and change movement. Linkages change the direction of a motion, cams change a spinning motion into a rise-and-fall movement, and gears and pulleys carry turning motion from one shaft to another and can change its speed. This module looks at linkages, rotary systems and how to work out a gear ratio.
Gear words
Learn these four terms before you study gears and gear ratios.
Cam or gear train?
Two common rotary systems do very different jobs.
The gear ratio
The gear ratio tells you how the speed changes. Gear ratio equals the number of teeth on the driven gear divided by the number of teeth on the driver gear. A larger driven gear turns more slowly but gives more turning force. Always show the division and give the ratio.
Match the mechanism
- a bell crank
- a cam and follower
- a pulley and belt
- a push and pull linkage
- changes the direction of a motion
- moves a part up and down
- carries turning motion between two shafts
- reverses the direction of a motion
Match the gear effect
- a larger driven gear
- a smaller driven gear
- a high gear ratio
- two equal sized gears
- the output turns more slowly
- the output turns more quickly
- more force but less speed
- the speed stays the same
What does a cam do?
What does a cam and follower do?
- It turns a spinning motion into an up-and-down movement.
- It changes the colour of a product.
- It stores electrical energy.
- It measures temperature.
Spot the rotary systems
Select the TWO mechanisms that are rotary systems.
- A gear train.
- A pulley and belt.
- A bell crank.
- A first order lever.
Work out a gear ratio
Put the steps of working out a gear ratio in order, earliest first.
- Count the teeth on the driver gear
- Count the teeth on the driven gear
- Divide the driven teeth by the driver teeth
- Write the answer as a ratio
Complete the mechanisms
The gear that is turned first is the _____ gear. The gear it drives is the _____ gear. A shaped wheel that lifts a follower up and down is a _____. A bar system that changes the direction of a movement is a _____. A larger driven gear makes the output turn more _____.
Calculate the gear ratio
A driver gear has 20 teeth and the driven gear has 60 teeth. Gear ratio = driven teeth divided by driver teeth. What is the first number of the gear ratio, when written against 1?
Find the linkages
Tap the TWO mechanisms that are linkages.
- a bell crank
- a gear train
- a push and pull linkage
- a pulley and belt
Which mechanism is it?
Read each description and choose which mechanism it is.
- A shaped wheel spins and pushes a follower up and down
- Two toothed wheels mesh to change the speed of a shaft
- A bar pivots to change the direction of a pushing movement
Explain a mechanism
Choose one mechanism from this module. Explain what it does and how it changes the motion, and give an example of where it could be used.
- Name the mechanism you have chosen
- Explain how it changes the motion
- Give an example of a product that could use it