Buoyancy & floating
Compare weight and buoyancy as an object displaces fluid, then find its floating level.
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 ↗Buoyancy & floating: common questions
Wondering about the why? Start here.
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.