Friction


1. A classroom desk supported by long legs is stationary in the room. A teacher comes around and pushes upon the desk in an effort to start it into a state of motion. The desk does not budge. The desk remains at rest because ______.
a. there is a force of static friction opposing its motion
b. there is a force of kinetic or sliding friction opposing its motion
 c. there is a force of rolling friction opposing its motion
d. there are small dust mites at the desk's feet that push back on the desk to keep it at rest

2. A classroom desk supported by long legs is stationary in the room. A teacher comes around and pushes upon the desk in an effort to start it into a state of motion. The desk is finally accelerated from rest and then moves at a constant speed of 0.5 m/s. The desk maintains this constant speed because ______.
a. there is a force of static friction balancing the teacher's forward push
b. there is a force of kinetic or sliding friction balancing the teacher's forward push
c. there is a force of rolling friction balancing the teacher's forward push
d. the teacher must have stopped pushing

3. The symbol µ stands for the _____
a. coefficient of friction b. force of friction c. normal force

4. The units on µ are _____
a. Newton b. kg c. m/s/s d. ... nonsense! There are no units on µ.

5. Use the friction equation and Fnet = m•a to fill in the blanks in the following situations.