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Buoyancy
Beginner
Upward force on an immersed body.
A fluid pushes up on immersed bodies because the pressure at the bottom is greater than at the top. The net upward force is the buoyant force.
You feel lighter in water.
Buoyancy acts on the part immersed only.
In more detail
Buoyancy is the upward force a fluid exerts on an object immersed in it, equal to the weight of the fluid displaced. It arises because pressure is greater at greater depth.
Real-world uses
- Ships float because their hulls displace enough water to balance their weight.
- Hot air balloons float because hot air is less dense than the surrounding air.
- Hot air balloons rise because the buoyant force from the cooler, denser air outside is larger than the weight of the balloon.
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Frequently asked questions
Why do objects float?
Because the buoyant force equals their weight when they displace their own weight in fluid.
Does buoyancy depend on depth?
No, in a uniform fluid, it depends only on the displaced volume.
Does buoyancy depend on the mass of the object?
No. It depends on the volume submerged and the density of the fluid, not on the object's own mass.
Related topics in Fluids & Elasticity
Barometer · Manometer · Gauge and absolute pressure · Archimedes' principle · Floating and sinking · Apparent weight in fluid