Pressure: Revision Notes (Form 5 SPM Physics)

What this chapter covers

• 2.1 Pressure in Liquids
• 2.2 Atmospheric Pressure
• 2.3 Gas Pressure
• 2.4 Pascal's Principle
• 2.5 Archimedes' Principle
• 2.6 Bernoulli's Principle

Key ideas explained

• 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.
• 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.
• 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.
• 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.

Formulas to memorise (none are given in the exam)

• P = F / A, Pressure, P = pressure (Pa); F = force (N); A = area (m²)
• P = hρg, Pressure in a liquid column, P = liquid pressure (Pa); h = depth (m); ρ = density (kg m⁻³); g = gravitational acceleration (m s⁻²)
• F₁ / A₁ = F₂ / A₂, Pascal's principle, F₁ = force on small piston (N); A₁ = area of small piston (m²); F₂ = force on large piston (N); A₂ = area of large piston (m²)
• Fb = ρVg, Buoyant force (Archimedes' principle), Fb = buoyant force (N); ρ = density of fluid (kg m⁻³); V = volume of fluid displaced (m³); g = gravitational acceleration (m s⁻²)

Experiments the DSKP names

• 2.1.2 · Investigate the factors affecting pressure in liquids
• 2.3.1 · Determine gas pressure using a manometer

Terms you must define precisely

• 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.
• Manometer, A U-shaped tube containing liquid used to measure the pressure of a gas by comparing liquid levels in its two arms.
• Pressure, The force acting normally (perpendicularly) on unit area of a surface (pressure = force ÷ area); measured in pascals (Pa).
• 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.
• 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.
• Gas pressure, The pressure produced by the collisions of gas particles with the walls of their container.
• Pascal's principle, Pressure applied to an enclosed fluid is transmitted equally and undiminished throughout the fluid in all directions.
• Hydraulic system, A system that uses Pascal's principle to multiply force by transmitting pressure through an enclosed liquid, as in a hydraulic jack.

A revision order that works

1. Finish with a timed set of calculations with units on every line.
2. Read the 6 standards above and tick the ones you can already explain aloud without notes.
3. Rewrite every definition in one sentence with the correct unit; definitions are the cheapest marks in Paper 2.
4. Derive each formula once from its meaning, then practise rearranging it before substituting numbers.
5. For each experiment, write the manipulated, responding and constant variables from memory, then the graph you would plot.

More Pressure resources

• Chapter overview: Pressure
• Common Mistakes
• Practice Questions
• 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)