The gravity is the sum of which two forces acting on a body?

• A. centrifugal force; buoyant force
• B. normal force; gravitational force
• C. gravitational force; buoyant force
• D. gravitational force; centrifugal force

Answer: (D)

In a rotating reference frame, the force that acts like gravity—the apparent gravity—is the vector sum of the true gravitational force and the centrifugal force. The centrifugal force is a fictitious force that arises because the frame is rotating, so when you combine it with gravity you get the effective weight a body experiences. This is why the pair describing apparent gravity is gravitational force plus centrifugal force. Normal force and buoyant force are real forces that come from contact and fluid pressure, respectively, and they don’t define the apparent gravitational pull in a rotating system.