Buoyancy & floating simulator
Lower an object into a fluid and compare its weight with the upward buoyant force. Archimedes’ principle says the buoyant force equals the weight of fluid displaced: Fᵦ = ρfluid × g × Vsubmerged. An object less dense than the fluid floats, with the fraction ρobject/ρfluid of its volume below the surface.
What if you changed…
Submerge a wooden block completely. Which way does the net force point?
See the calculation
- Volume = 2 L = 0.002 m³. Submerged volume = 0.001 m³.
- Buoyancy = ρfluid g Vsubmerged = 9.81 N. Weight = ρobject g V = 9.81 N.
- At equilibrium, submerged fraction = ρobject/ρfluid = 50%.
What this model assumes
Uniform fluid and object. Submerged fraction is set by the control. Only gravity and buoyancy are shown; drag and any external force holding the object are excluded. g = 9.81 m/s².
Keep an eye on this
Buoyancy depends on the submerged volume, not always the total object volume. The selected immersion is a snapshot, not necessarily equilibrium.
Understand the physics ↗Formulas used in this simulation
- Buoyant force (Archimedes’ principle)
- Fᵦ = ρfluid g Vsubmerged
- Weight of the displaced fluid
- Weight of the object
- W = ρobject g V
- Mass × g
- Floating fraction
- Vsubmerged / V = ρobject / ρfluid
- Only when ρobject < ρfluid
- Apparent weight underwater
- Wapparent = W − Fᵦ
- What a spring scale reads
Buoyancy & floating: common questions
Wondering about the why? Start here.
What is the formula for buoyant force?
Fᵦ = ρfluid × g × Vsubmerged. Use density in kg/m³, g in m/s² and volume in m³ to get newtons. A fully submerged 1 L object in water feels about 9.81 N of buoyancy.
Why do steel ships float?
A hull encloses a large volume of air, so the ship’s average density is less than that of water. It settles until it displaces water weighing as much as the whole ship.
Does buoyancy depend on depth?
For a rigid object fully submerged in an incompressible fluid, no. The pressure difference between its top and bottom is the same at any depth.
Why does a dense object sink?
If its density exceeds the fluid density, even full immersion cannot displace enough fluid for buoyancy to balance its weight. The net force is downward.
What happens if object and fluid densities are equal?
When fully submerged, weight and buoyancy balance. This is neutral buoyancy in the ideal uniform-fluid model.