Density, Pressure and Upthrust

Interactive Simulator · Density, pressure and upthrust

Float or Sink

A 1 litre block is lowered into a liquid. The liquid pushes up with an upthrust equal to the weight of the fluid it displaces, F = ρgV. If the block is less dense than the liquid it floats, sinking only far enough for the upthrust to match its weight; if it is denser, it sinks. Compare the weight and upthrust arrows, drawn to the same scale.

Mission Change the densities and find the rule for whether the block floats or sinks. Streak 0Best 0

Block density 600 kg/m³

Liquid density 1000 kg/m³

The block floats when its density is:

weight W = ρ_block g V5.9 N

maximum upthrust ρ_liq g V (fully under)9.8 N

fraction submerged when floating0.60

resultfloats

Upthrust = weight of displaced fluid = ρgV. Pressure rises with depth as Δp = ρgΔh, so the deeper face is pushed harder, giving a net upward force.