A person stands on a horizontal surface with gravity and normal forces only. If the person is not accelerating vertically, what is the net vertical force?

A person stands on a horizontal surface with gravity and normal forces only. If the person is not accelerating vertically, what is the net vertical force?

• A. The net vertical force is zero.
• B. mg
• C. N
• D. N − mg

Answer: (A)

When vertical acceleration is zero, the vertical forces must balance, so their sum is zero. On a person standing on a horizontal surface, gravity pulls downward with magnitude mg, and the ground pushes upward with the normal force N. The net vertical force is N - mg. Since there is no vertical acceleration, N must equal mg, making the net vertical force zero.

When vertical acceleration is zero, the vertical forces must balance, so their sum is zero. On a person standing on a horizontal surface, gravity pulls downward with magnitude mg, and the ground pushes upward with the normal force N. The net vertical force is N - mg. Since there is no vertical acceleration, N must equal mg, making the net vertical force zero.