1. Drop a boulder in a deep well. As it descends beneath the surface, pressure on it increases. Does this imply that buoyant force likewise increases?
2. Since buoyant force is the upward force that a fluid exerts on a body, and we learned that forces produce accelerations, why doesn’t a submerged body accelerate?
1. No! Once the boulder is beneath the water surface, it has displaced all the water it can. The water level in the well stays the same as the boulder further descends, showing that water displacement, and therefore buoyant force on the boulder, remains the same—even though water pressure on the boulder increases with depth. Buoyancy and pressure are different
concepts.
2. It does accelerate if the buoyant force is not balanced by other forces that act on it—the force of gravity and fluid resistance. The net force on a submerged body is the result of the force the fluid exerts (buoyant force), the weight of the body, and, if the body is moving, the force of fluid friction. When the net force is zero, the body is in equilibrium.