Grade 8 · Science · Unit 17 of 22
Gears, Pulleys & Efficiency
Speed ratios, force ratios and why friction matters
What your child practises
How gears trade speed for force, how pulleys and screws are used, how to calculate efficiency, and how designers weigh efficiency against effects on people and the environment.
Alberta Curriculum learning outcome: Unit D: Mechanical Systems · gears, belts and pulleys that transmit force and motion, speed and force ratios, efficiency, and how mechanical devices have changed over time
Sample questions
A taste of this unit. In the app, questions change every time and get easier or harder to match your child.
Question 1
A bicycle chain connects two gears. Which system is this?
- a chain drive, which transmits motion between shafts
- an electric circuit
- a hydraulic lift
- a pneumatic drill
Show answer
a chain drive, which transmits motion between shafts
Hint: Belts and chains carry motion from one wheel or gear to another.
Question 2
A small gear drives a large gear. What happens to the force?
- The force increases and the speed decreases.
- Both stay exactly the same.
- Both increase.
- The force decreases and the speed increases.
Show answer
The force increases and the speed decreases.
Hint: A driver with fewer teeth turning a driven gear with more teeth trades speed for force.
Question 3
What does a grain auger use to move grain up a tube?
- a mirror
- a magnet
- a rotating screw
- a lens
Show answer
a rotating screw
Hint: The same idea as Archimedes' screw: turning a screw moves material along a tube.
Question 4
A fixed single pulley mainly…
- halves the distance
- removes friction
- doubles the force
- changes the direction of the force
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changes the direction of the force
Hint: A fixed pulley lets you pull down to lift up, but the force stays about the same.
Question 5
Why should a mechanical device be evaluated for its impact on the environment as well as its efficiency?
- A very efficient device might still cause pollution or use up resources.
- The environment is not affected by machines.
- Impact cannot be measured.
- Efficiency is the only thing that matters.
Show answer
A very efficient device might still cause pollution or use up resources.
Hint: Good design considers cost, safety, efficiency and effects on people and nature.
Question 6
A driver gear with 10 teeth turns a driven gear with 40 teeth. The driver makes 24 full turns. How many full turns does the driven gear make?
answer box
Show answer
6
Hint: The driven gear has 4 times as many teeth, so it turns 4 times as slowly: 24 ÷ 4 = 6.