Short Answer

Buoyant force is the upward force that a fluid (liquid or gas) exerts on an object when the object is placed in it. This force acts opposite to the weight of the object and makes the object feel lighter in the fluid.

Buoyant force is responsible for floating and sinking. If the buoyant force is greater than or equal to the weight of the object, the object floats. If the buoyant force is smaller, the object sinks. This upward force arises because fluid pressure increases with depth.

Detailed Explanation :

Buoyant force

Buoyant force is a key concept in fluid mechanics that explains why objects float or sink when placed in a fluid. A fluid can be a liquid like water or a gas like air. Whenever an object is fully or partly immersed in a fluid, it experiences an upward push. This upward push is called the buoyant force. It always acts opposite to gravity.

Buoyant force is created because of the pressure difference in the fluid at different depths. Since pressure at the bottom of an object is greater than at the top, the object experiences an upward force. This force helps many objects float, makes people feel lighter in water, and allows balloons to rise in the air.

Meaning of buoyant force

The buoyant force can be defined as:

“The upward force exerted by a fluid on an object placed in it.”

It is also called upthrust. The magnitude of the buoyant force depends on the amount of fluid displaced by the object. The more fluid an object displaces, the greater the buoyant force acting on it.

Buoyant force is closely related to Archimedes’ principle, which describes how the strength of this upward force is determined.

Why buoyant force acts on objects

Buoyant force exists because of fluid pressure.

• Pressure in a fluid increases with depth.
• The bottom of an immersed object is deeper, so it experiences more pressure.
• The top of the object experiences less pressure.
• This difference in pressure produces an upward force.

This upward force tries to lift the object, creating the buoyant force.

Without this pressure difference, objects would not float or feel lighter in water.

Behaviour of objects under buoyant force

Depending on the relationship between the buoyant force and the weight of the object, three things can happen:

1. Object floats

An object floats when:

Buoyant force > Weight of the object

The upward force is strong enough to balance or exceed the object’s weight.

Example:
Wood, plastic, and cork float because they are less dense than water.

2. Object sinks

An object sinks when:

Buoyant force < Weight of the object

Here, the upward push is too weak to support the object.

Example:
A stone sinks because it is denser than water.

3. Object remains suspended

An object stays suspended when:

Buoyant force = Weight of the object

The object neither rises nor sinks, but stays at a fixed level.

Example:
A fish adjusts its swim bladder to stay at a certain depth.

Factors affecting buoyant force

Buoyant force depends on several factors:

1. Volume of fluid displaced
   More volume displaced → greater buoyant force.
2. Density of the fluid
   Denser fluid → stronger buoyant force.
   Example: Objects float more easily in seawater than freshwater.
3. Depth
   Pressure increases with depth, contributing to buoyant force.
4. Shape of the object
   Wide objects displace more fluid and experience greater upward force.

The buoyant force does not depend on the depth of the object itself but on how much fluid is displaced.

Examples of buoyant force in daily life

1. Floating boats and ships
   Ships float because their shape displaces a large volume of water, creating strong buoyant force.
2. Swimming
   Swimmers feel lighter because the water provides upthrust.
3. Ice floating on water
   Ice has lower density than water, so the buoyant force makes it float.
4. Helium balloons rising
   The buoyant force from air pushes the balloon upward.
5. Object rising to the surface
   A ball pushed underwater comes up quickly due to buoyant force.
6. Submarines
   Submarines control buoyant force by adjusting water in their tanks to sink, rise, or stay at a level.

Importance of buoyant force in science and technology

Buoyant force is essential in designing:

• Ships and boats
• Submarines
• Life jackets
• Hydrometers
• Hot air balloons
• Water-based amusement rides

It is also important in understanding:

• Atmospheric science
• Ocean currents
• Behaviour of gases in air
• Living organisms in water
• Fluid displacement measurements

Buoyant force influences many natural processes, such as the floating of icebergs and the movement of fish in oceans.

Conclusion

Buoyant force is the upward force exerted by a fluid on an immersed object. It arises due to the pressure difference at different depths in the fluid. Whether an object floats, sinks, or stays suspended depends on the comparison between buoyant force and its weight. Buoyant force plays an important role in everyday life and is the basis of many technologies, including ships, submarines, and balloons. Understanding buoyant force helps explain many natural and practical phenomena.