In which condition does the buoyancy force come into play for an immersed body?

Buoyancy force is a key concept in fluid mechanics, acting on an object submerged in a fluid. This force arises from pressure differences in the fluid: the pressure exerted on the lower part of the immersed body is greater than the pressure on the upper part due to the weight of the fluid above. As a result, this pressure difference generates an upward buoyant force.

The principle of buoyancy is most clearly defined when the body is at rest. In this condition, any movement of fluid around the body will not affect the forces acting on it significantly; hence, the buoyant force can be calculated based solely on the volume of fluid displaced by the body. When the body is in equilibrium, the buoyant force balances the weight of the body, determining whether it sinks, floats, or remains suspended in the fluid.

In conditions where the body is moving or when the fluid is still, the buoyant effects and the resultant forces can be more complex or influenced by additional factors such as fluid dynamics or drag forces. However, the fundamental principle of buoyancy is most straightforward and applicable when the body is at rest in the fluid.