5 · IGCSE Physics
Density and floating
Drop cubes of different materials into water, oil or glycerol. Read the mass, volume and density, see whether each one floats, and measure volume from the rise in liquid level.
ρ = m ÷ V
V(cube) = reading after − reading before
floats if ρ(cube) < ρ(liquid)
floating: fraction under = ρ(cube) ÷ ρ(liquid)
V(cube) = reading after − reading before
floats if ρ(cube) < ρ(liquid)
floating: fraction under = ρ(cube) ÷ ρ(liquid)
Try this
- Drop ice into water, then into paraffin oil. Use the two densities to explain the different results.
- Drop a pine cube and note the volume reading change. Tick the pin box: which reading gives the true volume of the cube?
- Choose aluminium and change V from 10 cm³ to 100 cm³. Check that m ÷ V stays the same, then do the same with nylon in water and in glycerol.
Common error: a floating object is only partly under the surface, so the rise in level gives its full volume only if it is pushed completely under the liquid.