1. The direction of a frictional force is always in a direction _______.

(a) opposite to the motion.

(b) in the same direction as the motion.

Explain your answer.

2. State what two kinds of coefficients of friction exist. Describe the conditions under which each kind is appropriate.

3. Suppose a block of mass 2.5.0 kg rests on a horizontal plane. and the coefficient of static friction wren the surfaces is 0.220.

a) What is the maximum static frictional force that could act on the block? Show your work.

b) What is the actual static frictional force that acts on the block if an external force of 25.0 N acts horizontally on the block?

In the experiment to measure the coefficient of kinetic friction by sliding a block down an inclined plane, it is required that the block move at constant velocity. Why is this requirement necessary?

5. Frictional forces on a block on an inclined plane are directed down the plane (TRUE/FALSE).

6. A 5.00 kg block rests on a horizontal plane. A force of 10.0 N applied horizontally causes the, block to move horizontally at a constant velocity. What is the coffiecient of kinetic between the block and the plane? Assume g = 9.81 m/ s2. Show your work.

7. What are the units of the coefficients of friction?

8. How does the force of friction depend on the apparent area of the two surfaces in contact?

(ie. the bigger the area, the the friction).

9. How does the coefficient of kinetic friction depend on the constant speed of a moving object?