When an object is submerged in a fluid, it experiences an upward force called buoyancy force. Buoyancy force is equal to the weight of the fluid displaced by the object. In other words, the more fluid an object displaces, the greater the buoyancy force it experiences.

The density of a fluid is defined as its mass per unit volume. The denser the fluid, the more mass it has for a given volume. Buoyancy force is directly proportional to the density of the fluid. This means that objects experience greater buoyancy force in denser fluids.

Water is denser than air. This means that objects experience greater buoyancy force in water than they do in air. This is why objects feel lighter underwater than when they are in air.

The amount of buoyancy force an object experiences is also affected by its shape. Objects with a large surface area experience greater buoyancy force than objects with a small surface area. This is because objects with a large surface area displace more fluid.

The combination of density and shape determines how much buoyancy force an object experiences. Objects that are less dense than the fluid they are submerged in will experience a greater buoyancy force than objects that are more dense than the fluid. Objects with a large surface area will also experience a greater buoyancy force than objects with a small surface area.

Buoyancy force is an important concept in many areas of physics, including fluid mechanics, naval architecture, and aeronautics.