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S3 Physics: Pressure and Buoyancy (Paper 1: basics)
S3 Physics: Pressure and Buoyancy (Paper 1: basics)
The three commonest errors are treating pressure as a force, using the area of one foot when a person stands on two, and thinking buoyancy exists only for floating objects. Write the formula first, then substitute.
Direct answers Most marks on the basics paper are lost on units and on using the total contact area rather than a single face.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 20 |
| Difficulty mix | Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1 |
| Chapter | Chapter: S3 Physics: Pressure and Buoyancy |
| Level | S3 Physics |
02 Questions (10 items)
- FoundationWhat is the formula for pressure?
- FoundationWhat is the unit of pressure and how does it relate to the newton?
- FoundationA force of 200 N acts on an area of 0.5 m2. What is the pressure?
- IntermediateA student weighing 600 N stands on both feet with a total sole area of 0.03 m2. What pressure does he exert on the floor?
- IntermediateIf the same force acts on half the area, what happens to the pressure?
- ChallengeWhat is the formula for pressure in a liquid?
- ChallengeWater has a density of 1 000 kg/m3 and g is 10 N/kg. What is the pressure at a depth of 2 m?
- IntermediateIn which direction does buoyancy act?
- ChallengeA block floats at rest on water. How does the buoyant force compare with its weight?
- Error redoWhat is wrong with the statement that the unit of pressure is the newton?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | p = F / A, pressure equals force divided by the contact area. | Pressure describes how much force acts on each unit of area, so area is in the denominator. |
| 2 | The pascal (Pa), where 1 Pa = 1 N/m2. | A force of one newton spread over one square metre is one pascal. |
| 3 | 400 Pa | p = F / A = 200 / 0.5 = 400 Pa. |
| 4 | 20 000 Pa | Use both feet together: 600 / 0.03 = 20 000 Pa. |
| 5 | It doubles | Area is in the denominator, so halving it doubles the pressure, which is why knife edges are sharpened thin. |
| 6 | p = rho g h, density times gravitational field strength times depth. | Liquid pressure depends only on density and depth, not on the shape of the container. |
| 7 | 20 000 Pa | p = rho g h = 1 000 x 10 x 2 = 20 000 Pa. |
| 8 | Vertically upward | Pressure from below is greater than from above, so the net effect is an upward buoyant force. |
| 9 | They are equal in size | At rest the net force is zero, so buoyancy exactly balances the weight. |
| 10 | Pressure is measured in pascals, while the newton measures force. | Mixing up units loses easy marks: force is in N and pressure in Pa or N/m2. |
04 What to do after marking
- After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
- Repeat the same item two days later; move to the next paper only when both attempts are correct.
- Parents only need the answer and note columns; there is no need to explain every item.
Three basics: pressure is force over area (p = F / A), solids depend on contact area while liquids depend on depth, and buoyancy always acts upward. Write the known values on one line before substituting.Tutor Registration →
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