Which statement best defines buoyant force?

• A. The downward force due to gravity
• B. The upward force exerted by a fluid on an immersed object
• C. The frictional force opposing motion through a fluid
• D. The force that holds a floating object down at the bottom

Answer: (B)

Buoyant force is the upward push a fluid gives to anything immersed in it. This happens because fluid pressure increases with depth, so the pressure on the bottom of the object is greater than the pressure on the top. The difference in pressure creates a net upward force. In fact, the magnitude of this upward force equals the weight of the fluid the object would displace if it were removed, which explains why objects float or rise to the surface when the displaced fluid’s weight matches the object’s weight. The other ideas describe gravity, frictional resistance, or a downward force, none of which capture the upward push from the fluid on the object.