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Archimedes' principle
Beginner
Buoyant force equals the weight of fluid displaced.
F_b = ρVgThe buoyant force equals the weight of the displaced fluid: F_b = ρ_fluid V_displaced g.
A 0.002 m³ ball fully immersed in water: 19.6 N.
The fluid's density counts, not the object's.
In more detail
Archimedes' principle states that an immersed object experiences an upward force equal to the weight of the fluid it displaces. This explains buoyancy for floating and submerged bodies.
Real-world uses
- Hydrometers use Archimedes' principle to measure liquid density.
- Submarines control buoyancy by changing their ballast.
- A submarine controls its depth by changing the water in its ballast tanks, which alters its average density and its buoyant force.
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Frequently asked questions
Who was Archimedes?
An ancient Greek mathematician and scientist who discovered this principle.
Does the object's weight matter?
Only in deciding whether it floats; the buoyant force depends on the fluid displaced.
Does a heavy object sink more than a light one?
Not by itself. Whether it sinks depends on its density compared with the fluid, not just its weight.
Related topics in Fluids & Elasticity
Manometer · Gauge and absolute pressure · Buoyancy · Floating and sinking · Apparent weight in fluid · Stability of floating bodies