Question

The force of friction always opposes motion or tendency of motion.
A) True
B) False

Answer 1

Hint: Friction is a force which is known as an opposing force to the motion as its direction is opposite to the direction of motion .It is not mandatory that it always results as an opposing force to motion as it helps to walk.

Complete Step by Step answer:
We can understand this by some example as:

Let us put a heavy box on the ground. When we push the box with a small force the box will not move. Since, frictional force is a self-adjusting force it will adjust the frictional force equal to the force we apply to the box. So, when we increase the force on the box, the frictional force on the box will also increase. When we apply more force than the threshold limit then only the box will move in the direction of the force. Even when the box is moving a friction force will act on the body which will oppose the applying force. So, in this case we can say that the friction opposes the motion.

But consider the case of walking on the surface of earth. When we walk, we push the ground with our foot in the backward direction. We know from Newton’s third law that every force has an equal and opposite reaction. Due to this backward push, the ground pushes us forward and we can walk on the ground. Or we can say that the forward friction helps us walk in the ground. Here, we get that the friction is not opposing the motion but, it helps with the motion.

By understanding above example and analyzing many other such phenomenon
In our surrounding we understand that the above given statement is false. Hence, option (B) is right.

Note:
Static friction plays its role when a body is at rest on the surface of another body means one of them is static with respect to another. This friction exists when an external force is applied on the body at rest.
Limiting Friction satisfies the condition of initiation of motion which means our body becomes ready to move due to external force at that point it has an upper limit of static frictional force working on it.
Kinetic or Dynamic Friction plays its role when the body is in actual motion under an external force where the applied force has capacity more than limiting frictional force.