Floatation

What is Floatation?

Floatation is the phenomenon where an object remains suspended at the surface or inside a fluid due to the upward force exerted by the fluid.

This upward force is known as buoyant force or upthrust.

Archimedes' Principle

It states that:

“When an object is partially or fully immersed in a fluid, it experiences an upward force equal to the weight of the fluid displaced by the object.”

Discovered by the Greek scientist Archimedes.

Conditions for Floatation

• If Weight = Buoyant Force → Object floats (neutral buoyancy)
• If Weight < Buoyant Force → Object rises (positive buoyancy)
• If Weight > Buoyant Force → Object sinks (negative buoyancy)

Buoyant Force

The upward force exerted by a fluid on a submerged object is called buoyant force.

• Buoyant Force ∝ Volume of fluid displaced

Density and Floatation

The ability of an object to float depends on its density compared to the density of the fluid.

• If object density < fluid density → floats
• If object density > fluid density → sinks

Previous Year Questions

• SSC CGL 2020: Which principle explains floatation?
• Archimedes' Principle
• RRB JE 2019: Why does a ship float on water?
• Because its average density is less than that of water
• HSSC JE 2017: What happens when an object’s density is greater than water?
• It sinks

Applications of Floatation

• Ships and boats float due to design that lowers average density.
• Hydrometers float higher or lower based on liquid density.
• Submarines change depth by adjusting their density using ballast tanks.

Conclusion

Floatation is governed by buoyant force and fluid displacement. Archimedes’ Principle explains this phenomenon and is widely applied in daily life, from shipping to scientific instruments.