How is the frictional force produced? please answer my question in simple language..

Animals respond in various ways to stimuli detected through their senses. some of these responses are stimulated by the presence of danger. which of these animal responses is the best example of a response to an immediate threat? a) a rooster crows every morning at the first sign of light. b) as something approaches an octopus, it shoots a cloud of ink. c) from late fall until spring, bears hibernate to preserve energy. reactivate d) a dog is getting hot in the sunlight, so he moves to a shaded area.

The long handle on a rake is a(n) a. lever b. screw c. wedge d. inclined plane

Why is the energy that results from a roller coaster's position at the top of a hill referred to as potential energy?