For the following situations, describe the contact and non-contact forces that are involved. A book sitting on a shelf
A soccer player kicking a ball; the ball soaring through the air and landing on the ground
A hiker in the woods reading her compass to determine which direction to go
A child on a sled; first, the child is sitting at the top of the hill, waiting his turn; then, the child pushes off and slides down the hill, eventually coming to a stop.

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.

b) phosphorus pentoxide

positive reinforcement? ?