ForcesTopic Summary
Knowledge Organiser: Pressure (P = F/A)
Part of Pressure · GCSE GCSE Physics revision
This topic summary covers Knowledge Organiser: Pressure (P = F/A) within Pressure for GCSE Physics. Revise Pressure in Forces for GCSE Physics with 15 exam-style questions and 12 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 16 of 16 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 16 of 16
Practice
15 questions
Recall
12 flashcards
Knowledge Organiser: Pressure (P = F/A)
Key Equations
- P = F / A — all tiers
- F = P × A — rearrangement
- A = F / P — rearrangement
- P = hρg — Higher Tier only
Key Units
- Pressure — Pascal (Pa) = N/m²
- Force — Newton (N)
- Area — square metres (m²)
- Depth — metres (m)
- Density — kg/m³
Key Concepts
- Smaller area → greater pressure (same force)
- Fluid pressure acts in all directions
- Fluid pressure increases with depth
- Atmospheric pressure decreases with altitude
- Upthrust = net upward force from pressure difference in fluid
Examples
- Sharp knife: tiny area → high pressure
- Snowshoes: large area → low pressure
- Deep sea diver: great depth → high fluid pressure
- Aircraft altitude: higher → lower atmospheric pressure
- Ship floating: upthrust = weight of ship
Common Mistakes
- Confusing force and pressure: A large force does not always mean large pressure — pressure depends on the area too; a small force over a tiny area creates high pressure
- Using wrong area units: Area must be in m² for pressure in Pascals — convert cm² by dividing by 10,000 (1 m² = 10,000 cm²)
- Forgetting fluid pressure depends on depth not volume: Pressure in a fluid increases with depth (p = h × ρ × g) — the total volume of fluid is irrelevant
- Confusing upthrust with weight: An object floats when upthrust equals weight — upthrust is the upward force from the fluid, not the weight of the object itself
- Applying surface pressure formula to fluid pressure: p = F ÷ A applies to solid surfaces; p = h × ρ × g applies to pressure at depth in a fluid — don't mix these up