Grade 8 · Science · Unit 7 of 13
Hydraulics & Pneumatics
Machines and bodies that move fluids
What your child practises
How hydraulic systems (liquids) and pneumatic systems (compressed air) work, where each is used, and how valves, pumps and tubes in machines compare with the heart, lungs and blood vessels.
Ontario Curriculum expectation: C2.8–C2.10 · factors that affect fluid flow, hydraulic and pneumatic systems, and how fluids are used and regulated in living things and in machines
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
Large trucks and buses often use air brakes. What is one advantage of air as the working fluid?
- Air is denser than oil.
- Air is more viscous than brake fluid.
- Air is free, plentiful and does not spill.
- Air cannot be compressed.
Show answer
Air is free, plentiful and does not spill.
Hint: A leak in an air system simply releases air.
Question 2
Which part of the heart has a job like a valve in a machine?
- the skin of the heart
- the blood itself
- the heart valves that keep blood flowing one way
- the ribs
Show answer
the heart valves that keep blood flowing one way
Hint: Valves stop fluid flowing backward.
Question 3
A pneumatic system leaks. Compared with a hydraulic leak, what is likely true?
- It always leaves a mess of oil.
- Air escapes without leaving oil on the ground.
- It can only lift the heaviest loads.
- It makes water.
Show answer
Air escapes without leaving oil on the ground.
Hint: Air leaks are noisy and waste energy, but they do not spill oil.
Question 4
A valve in a hydraulic or pneumatic system is used to…
- make the fluid colder
- change the fluid into a solid
- store the fluid forever
- regulate or direct the flow of the fluid
Show answer
regulate or direct the flow of the fluid
Hint: Valves open, close or redirect the flow.
Question 5
A hydraulic system uses a…
- magnet
- liquid, usually oil
- solid rod only
- compressed gas
Show answer
liquid, usually oil
Hint: Hydraulic systems transmit force through a liquid.
Question 6
Why do hydraulic systems use liquids instead of gases?
- Gases cannot be used in machines.
- Liquids are lighter than gases.
- Liquids can be squeezed easily.
- Liquids are almost incompressible, so force is passed on strongly and quickly.
Show answer
Liquids are almost incompressible, so force is passed on strongly and quickly.
Hint: Compressing a gas wastes some of the force.