Floating | Physics for GCSE/IGCSE - Year 11 PDF Download

Floating Objects

Upthrust

• Upthrust Definition: Upthrust is a force that pushes objects upward when they are submerged in fluids like liquids and gases
• Opposes Weight: It always acts in the opposite direction to the object's weight, which clarifies why objects less dense than the fluid, like boats, float.
• Determining Factors: The intensity of upthrust is influenced by the density of the fluid and the volume of fluid displaced, equivalent to the object's volume.
• Fluid Density Impact: Objects experience a greater upthrust in denser fluids due to the increased push exerted by the fluid.

Factors Affecting Floating & Sinking

• Whether an object sinks or floats is determined by the relationship between upthrust and the object's weight.
  • If the upthrust is equal to or greater than the object's weight, the object will float.
  • Conversely, if the upthrust is less than the weight of the object, it will sink.
• Outcome Dependence on Object's Density
  • The outcome of whether an object floats or sinks in a fluid depends on the object's density in relation to the density of the fluid it is immersed in.

• Density and Floating/Sinking

  • If the object's density is less than the density of the fluid, it will float. However, if the object's density is greater than the density of the fluid, it will sink.

• A polystyrene block will float in water due to its low density of 0.05 g/cm³, significantly less than water's density of 1.0 g/cm³.
• A wooden block will float partially submerged because its density (0.9 g/cm³) is slightly lower than that of water.
• An iron block will sink since its density (7.9 g/cm³) is much higher than water's.

Floating Liquids

If two liquids with different densities that don't mix are involved, the one with lower density will float on top of the one with higher density.