A large crate filled with physics laboratory equipment must be moved up an incline onto a truck. Required:
a. The crate is at rest on the incline. What can you say about the force of friction acting on the crate?
b. A physicist attempts to push the crate up the incline. The physicist senses that if he applies slightly more force the crate will move up the incline but cannot muster enough strength to get the motion started. What can you say now about the force of friction acting on the crate?
c. The first physicist gets a second physicist to help. They both push on the crate, parallel to the surface of the incline, and it moves at constant speed up the incline. How does the force exerted by the two physicists on the crate compare with the force of friction on the crate?