GCSE Physics (AQA)

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Floating & Sinking

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Forces Pressure and pressure differences in fluids

Floating & Sinking

7:10 Depth and Atmospheric Pressure
Spec 4.5.5.1.2
Previous Upthrust Next Atmospheric Pressure
  • An object in a fluid will either float to the surface or sink down.
  • Floating and sinking can apply to both liquids and gases, but GCSE focuses on liquids.
  • Whether an object floats or sinks depends on the balance between its weight and the upthrust acting on it.
  • Weight is a downward force due to gravity, while upthrust is an upward force due to pressure differences.
  • Objects will sink if their density is greater than the fluid they are in.
  • Dense materials are used for objects designed to sink, like anchors.
  • Sea water is denser than pure water due to dissolved salt.
  • Pure water has a density of 1000 kg/m��.
  • Objects will float if their density is less than the fluid they are in.
  • Large objects like cruise ships can float due to having a density less than water, despite their large mass.
  • The density of an object is calculated by dividing its mass by its volume.
  • Ships are mostly empty space, which increases volume without significantly increasing mass, resulting in lower density.
  • Objects float partially submerged because the upthrust decreases with less submerged volume.
  • At the surface, objects stabilize when upthrust balances weight.
  • Greater density results in more of the object being submerged when floating.
  • More submerged volume means greater upthrust is needed, indicating greater weight and density.
  • Understanding the relationship between submerged volume, upthrust, weight, and density is important for exams.

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