Physics · Simulator 020
Drop a block into a tank of liquid. Change the block's density and size and the liquid's density, predict whether it floats and how deep it sits, then let it settle and compare the buoyant force with its weight.
A submerged object pushes aside (displaces) fluid. Archimedes' principle says the upward buoyant force equals the weight of the displaced fluid:
F_b = ρ_fluid · V_submerged · g
The object's weight is ρ_object · V · g. If the object is less dense than the fluid it floats, sinking until the buoyant force matches its weight. The fraction below the surface is then
V_submerged / V = ρ_object / ρ_fluid
If it is denser, even full submersion can't provide enough lift, and it sinks to the bottom. There the floor supplies the rest of the support, and the readout shows its apparent weight.
The animation adds water drag so the block settles smoothly, bobbing a little before it comes to rest.
Uniform cube, rigid, upright, no surface tension, fluid level change in the tank neglected. Densities are typical values.
A wooden cube floats in water with 60% submerged. What is its density? In which liquid would it float exactly half-submerged?
ρ_wood = 0.60 × 1000 = 600 kg/m³. For 50% submerged you need ρ_fluid = 600/0.5 = 1200 kg/m³, roughly glycerine (≈1260) or a strong salt solution. Try a custom liquid of 1200 kg/m³.