This higher tier covers Higher Tier: Pressure in Fluids and Upthrust within Density for GCSE Physics. Revise Density in Particle Model for GCSE Physics with 13 exam-style questions and 30 flashcards. This topic shows up very often in GCSE exams, so students should be able to explain it clearly, not just recognise the term. It is section 10 of 13 in this topic. This section is most useful once the core foundation idea is secure, because it adds the detail that pushes answers higher.
🎓 Higher Tier: Pressure in Fluids and Upthrust
Pressure in a fluid increases with depth according to: P = ρ × g × h
- P = pressure (Pa)
- ρ = density of the fluid (kg/m³)
- g = gravitational field strength (10 N/kg)
- h = depth below surface (m)
Upthrust arises because pressure is greater at the bottom of a submerged object than at the top. This pressure difference creates a net upward force.
Archimedes' Principle: The upthrust on an object equals the weight of fluid it displaces. If upthrust ≥ weight of object, the object floats.
This explains why a steel ship floats — its hollow shape displaces a large volume of water, so upthrust equals its weight even though steel itself is much denser than water.
Practice questions for Density
What is the correct equation for density?
Explain why gases have a much lower density than solids, using ideas about particles.