Grade 8 · Science · Unit 6 of 13
Pressure & Pascal's Law
Squeezing, heating and passing on force
What your child practises
Why gases compress easily and liquids do not, how heating or compressing a fluid changes its pressure and volume, and how a hydraulic press uses Pascal's law to multiply a force.
Ontario Curriculum expectation: C2.4, C2.6, C2.7 · compressibility of liquids and gases, how pressure, volume and temperature are related, and Pascal's law
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 hydraulic press has a small piston with an area of 4 cm² and a large piston with an area of 24 cm². A force of 10 N pushes on the small piston. What force does the large piston exert, in N? Ignore friction.
answer boxN
Show answer
60 N
Hint: The pressure is the same on both pistons, so the force grows by the same ratio as the area.
Question 2
A force of 1000 N pushes on an area of 5 m². What is the pressure in Pa (N/m²)?
answer boxPa
Show answer
200 Pa
Hint: Pressure = force ÷ area.
Question 3
You push the plunger of a sealed syringe full of water. The water's volume…
- hardly changes
- doubles
- becomes zero
- is cut in half
Show answer
hardly changes
Hint: Liquids are nearly incompressible.
Question 4
Is each fluid easy to compress, or very hard to compress?
Sort into: 🎈 Easy to compress · 🧱 Very hard to compress
- 🫒cooking oil
- ♨️steam
- 🚲air in a bicycle pump
- 🤿gas in a scuba tank
- 🛢️hydraulic oil
- 🎈helium in a balloon
- 🛞brake fluid
- 💧water in a sealed bottle
Show answer
🎈 Easy to compress: steam, air in a bicycle pump, gas in a scuba tank, helium in a balloon · 🧱 Very hard to compress: cooking oil, hydraulic oil, brake fluid, water in a sealed bottle
Hint: Gases are easy to compress because their particles are far apart. Liquids are very hard to compress.
Question 5
A hydraulic jack lifts a car. Which property of liquids makes this possible?
- They are easy to compress.
- They are almost incompressible and transmit pressure.
- They expand when pushed.
- They have no mass.
Show answer
They are almost incompressible and transmit pressure.
Hint: Pressure goes through the liquid to the larger piston.
Question 6
Why are liquids hard to compress?
- Their particles are already close together.
- Their particles are all frozen in place.
- Their particles do not exist.
- Their particles are very far apart.
Show answer
Their particles are already close together.
Hint: There is very little empty space to squeeze out.