When an object is not moving in a fluid, the force exerted on it by the fluid is called buoyant force.

Here's a breakdown:

* Buoyant force is an upward force that opposes the weight of an object submerged in a fluid.

* It's caused by the difference in pressure between the top and bottom surfaces of the object. The pressure at the bottom is higher due to the weight of the fluid above it.

* This pressure difference creates an upward force that pushes the object upwards.

Important Note: Even though the object isn't moving, the fluid is still exerting a force on it. This force is in equilibrium with the object's weight, meaning they cancel each other out, resulting in no net movement.