Question

How does friction affect an object’s motion?

Answer 1

Hint: Recall that friction is essentially a force that is always directed opposite to the motion of an object. Use this intuitive understanding to deduce the role played by friction in different types of motions and states of motion. Remember that the friction acting on an object is directly proportional to the area of contact between the object and the surface over which it executes motion and arises as a result of relative motion between the two surfaces.

Complete Solution:
Let us begin by first establishing an understanding of what friction means following which we shall classify and explore the different types of friction.

A resistive force that opposes relative motion between surfaces, friction converts kinetic energy arising from the motion of one object in contact with the other into thermal energy or heat. Though friction is a resistive force, it is not necessarily an undesirable consequence. Friction is essential in providing traction and grip to automobiles in motion, we are able to start a fire by rubbing two pieces of wood together, we can ignite matchsticks due to friction between the head of the match and the rubbing surface on the matchbox, we are able to stand on the ground, or hold things in our hands, all due to friction.

Based on the type of relative motion, friction can be classified into:
1. Static friction: It is the force of friction acting between two surfaces that have no relative motion with respect to each other, i.e., they are at rest with respect to each other. Thus, static friction is in essence, the amount of force that must be applied to just set up the two surfaces in relative motion.

2. Sliding friction: It is the resistive force acting between two objects that are sliding against each other. It opposes the relative motion between the two surfaces.

3. Rolling friction: It is the resistive force that opposes the objects that are in relative rolling motion, and at all times, the friction acts only at the point of contact between the two surfaces.

In addition to this, there are other types of friction, such as fluid friction (which is the friction that exists between layers of fluid when there are in relative motion with respect to each other), internal friction (resistive force acting under deformation, between elements that make up a solid), and so on.

Thus, we can conclude that friction always opposes the relative motion between two surfaces in contact with each other and is a resistive force acting in a direction opposite to any applied force.

Note:
Note that sliding friction and rolling friction are basically classifications under kinetic friction (friction arising during motion), and sometimes, static and kinetic friction are grouped together as dry friction. Also, the weakest of all friction that we discussed above is rolling friction since at any given time, the point of contact between the two surfaces is minimum in comparison to the other forms of friction.