Friction

Question 1

It is a force that opposes the motion of two surfaces that are in contact with each other.

Answer 1

Friction

Question 2

Two types of friction

Answer 2

Static and Kinetic Friction

Question 3

Is it the type of friction force where the force is exerted on one surface by another when there is no motion between the two surfaces.

Answer 3

Static friction

Question 4

It is a type of friction force where is exerted on one surface by another when two surfaces rub against each other because one or both of them are moving.

Answer 4

Kinetic friction

Question 5

• Matter is not as smooth on its surface as it appears to be; tiny irregularities get “stuck” on one another.
• On very smooth surfaces, the atoms can become so close that there are electrical forces acting between them.
• Sliding object’s often experience “jerky” motion as bonds or “Jags” are broken.

Answer 5

Causes of friction

Question 6

The coefficient of static friction is greater than kinetic friction.

Answer 6

True

Question 7

Suppose that the coefficients of static and kinetic friction have values such that for a crate in contact with a cement floor. Which one of the following statements is true?

A. The magnitude of the static frictional force is always 1.4 times the magnitude of the kinetic frictional force.
B. The magnitude of the kinetic frictional force is always 1.4 times the magnitude of the static frictional force.
C. The magnitude of the maximum static frictional force is 1.4 times the magnitude of the kinetic frictional force.

Answer 7

C. The magnitude of the maximum static frictional force is 1.4 times the magnitude of the kinetic frictional force.

Question 8

A box rests on the floor of an elevator. Because of static friction, a force is required to start the box sliding across the floor when the elevator is

(a)stationary,
(b)accelerating upward, and
(c)accelerating downward. Rank the forces required in these three situations in ascending order—that is, smallest first.

Answer 8

c, a, b