Questions
1. Calculate: A force F = 200 N acts over an area A = 0.5 m². Find the unknown using P = F / A.
P = F / A = 200 / 0.5 = 400 Pa.
2. Calculate: Find the pressure at depth h = 2.0 m in water (ρ = 1000 kg m⁻³, g = 9.81 m s⁻²). Find the unknown using P = hρg.
P = hρg = 2.0 × 1000 × 9.81 = 19620 Pa ≈ 1.96 × 10⁴ Pa.
3. Calculate: A hydraulic system: F₁ = 20 N on A₁ = 0.01 m² acts on a piston of A₂ = 0.05 m². Find the unknown using F₁ / A₁ = F₂ / A₂.
F₂ = F₁ × A₂ / A₁ = 20 × (0.05 / 0.01) = 100 N.
4. Calculate: An object displaces V = 2.0 × 10⁻³ m³ of water (ρ = 1000 kg m⁻³, g = 9.81 m s⁻²). Find the unknown using Fb = ρVg.
Fb = ρVg = 1000 × 2.0 × 10⁻³ × 9.81 = 19.62 N ≈ 19.6 N.
5. State the manipulated, responding and constant variables for: To investigate the relationship between the depth below the surface of a liquid and the pressure at that depth.
Manipulated: Depth below the liquid surface, h. Responding: Pressure, shown by the height difference in the manometer, H. Constant: The same liquid (same density).
6. State the manipulated, responding and constant variables for: To determine the pressure of a gas supply using a liquid column manometer.
Manipulated: Setting of the gas supply (flow rate). Responding: Height difference of the liquid columns, h. Constant: Atmospheric pressure and the density of the manometer liquid.
7. Explain: why pressure increases with depth.
The deeper you go, the more water lies above you, and its weight presses down. So water pressure grows steadily with depth, not with the shape or width of the container.
8. Explain: how a hydraulic jack lifts a car.
Pressure applied to a trapped liquid is passed on equally throughout it. A small force on a small piston creates a pressure that pushes a large piston with a much bigger force.
9. Explain: why ships float even though they are heavy.
A floating object pushes aside water whose weight equals its own. A steel ship is hollow, so it displaces enough water to support its weight and floats, even though steel itself sinks.
10. Explain: how an aeroplane wing generates lift.
Air moves faster over the curved top of a wing than underneath. Faster-moving air has lower pressure, so the higher pressure below pushes the wing up, giving lift.
11. Define principle of flotation.
A floating object displaces a weight of fluid equal to its own weight.
12. Define bernoulli's principle.
For a flowing fluid, where the speed is higher the pressure is lower, and where the speed is lower the pressure is higher.
13. Define manometer.
A U-shaped tube containing liquid used to measure the pressure of a gas by comparing liquid levels in its two arms.
14. Define pressure.
The force acting normally (perpendicularly) on unit area of a surface (pressure = force ÷ area); measured in pascals (Pa).
15. Define pressure in liquids.
The pressure at a point in a liquid, which increases with depth and density (pressure = height × density × gravitational field strength) and acts equally in all directions.
16. Define atmospheric pressure.
The pressure exerted by the weight of the column of air in the atmosphere on the Earth's surface and on objects in it.
Marking yourself
- Calculation: formula written, values substituted with units, final answer with unit and sensible significant figures.
- Variables: manipulated = what you change; responding = what you measure; constant = what you keep the same.
- Definition: one sentence, correct physical quantity, correct unit.
Exam tip
More Pressure resources
- Chapter overview: Pressure
- Revision Notes
- Common Mistakes
- Paper 2 Answering Guide
- Paper 3 Guide
- Key Terms
- Calculation practice sets
Source: DSKP KSSM Physics Form 4 and 5 (Versi English), Sijil Pelajaran Malaysia: Format Pentaksiran mulai 2021, Fizik (4531) (Bahagian Pembangunan Kurikulum (BPK), KPM)