Below is a picture of a hand holding a ball against a wall. The
student is asked to describe all of the forces acting on the
ball.
The hand is pushing the ball both up and to
the right. Gravity is pulling down on the ball. Since the ball is not
moving, it is certainly not accelerating, so the net force must be
zero. The wall must be exerting a force to the left (normal force) to
cancel the rightward component of the force exerted by the hand. The
wall may (or may not) be exerting a frictional force on the ball,
depending on the relative magnitudes of the weight and the upward
comonent of the force of the hand. If the weight is larger (smaller)
than the upward component, the wall must exert an upward (downward)
frictional force on the ball.
This website was written by Tom
Brown and Jeff
Crowder. Please let us know if you encounter any
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