Answer:
a. the book is exerting force down on the shelf (due to gravity) while the shelf is exerting force back up at the book.
b. when the soccer player kicks the ball, this is applied force. As the ball soars through the air and lands on the ground, the friction ends the movement of the ball.
c. the compass detects the Earth's natural magnetic feild. This force is non contact, since there is no physical touch between magnetic feilds and the compass.
d. when the child is just sitting on the hill on the sled, this is a contact force. The child is pushing down on the sled and the sled pushes back at the child. When he or she slides off down the hill, this contact force is put to a stop due to friction.
Explanation:
Explanation above for each situation.
