Buoyancy is the upward push a fluid gives an object — equal to the weight of fluid it displaces (Archimedes' principle). Drag the sliders below to change the object density, object volume and fluid density, and watch it float or sink while the buoyant force and apparent weight respond in real time.
The identical metal that keeps a loaded hull riding high sends a dropped bolt straight to the seabed, and this simulator settles that paradox with one dial. Raise Object density above Fluid density and the status flips to Submerged; drop it below and the object FLOATS. The Buoyant force readout equals the weight of the fluid pushed aside, F_b = ρ_fluid · V_displaced · g — the object's whole volume once it is fully under — while Weight tracks W = ρ_object · V · g. Only the comparison of the two densities decides the outcome.
Reach for the Object volume slider expecting a bigger block to sink, and watch the trap spring: weight and the full-submersion buoyant force both scale with litres in lockstep, so a large slab and a small one made of the same material share the same verdict. A floating object settles when it has displaced its own weight of fluid, so Buoyant force equals Weight and Apparent weight reads zero, sitting a fraction ρ_object / ρ_fluid deep. Push density past the fluid and apparent weight climbs to (ρ_object − ρ_fluid) · V · g.
The steel ship earns its float on average density — hull plus trapped air — not the 7800 kg/m³ of solid plate, a nuance you can rebuild by nudging Object density down toward water. Put a hull number to the pull with the buoyancy calculator, then wander into another force waiting on the shelf of interactive physics sims.
Archimedes' principle states that the upward buoyant force on an object equals the weight of the fluid it displaces: F_b = ρ_fluid·V_displaced·g. It is why objects feel lighter in water and why some float.
The comparison of densities. An object floats when its density is less than the fluid's, and sinks when it is greater. Its volume and total weight alone do not decide it — a large and a small block of the same material behave the same way.
A floating object sinks until it has displaced exactly its own weight of fluid. At that point the buoyant force equals its weight, the two cancel, and its apparent weight reads zero. It rides with a fraction ρ_object/ρ_fluid of its volume submerged.
A ship is mostly hollow, so its average density — steel hull plus the air inside — is well below that of water. That low average density lets it displace enough water to match its weight, even though solid steel (about 7800 kg/m³) sinks.