Q14DQ - University Physics with Modern Physics

Question

It is often said that “friction always opposes motion.” Give at least one example in which (a) static friction causes motion, and (b) kinetic friction causes motion.

 

Step-by-Step Solution

Answer

(a) Walking in the sidewalk in a horizontal direction.

(b) Driving in a curve of highway.

 

Step 1: Significance of the friction

The friction is described as the force that mainly resists the motion of an object. The frictional force is equal to the product of the frictional coefficient and the normal force.

Step 2: Determination of the examples of the cases

(a) Walking in the sidewalk in a horizontal direction. Here, without the static friction, the feet would have slide in the backward direction that is relative to the ground. Hence, the static friction causes motion in this example.

 

(b) Driving in a curve of highway. Here, without the kinetic friction, the car cannot change its direction and also move forward. Hence, the kinetic friction causes motion in this example.

 

Thus, 

(a) Walking in the sidewalk in a horizontal direction.

(b) Driving in a curve of highway.