Question

Give examples to show that friction is both a friend and a foe.

Answer 1

We know that friction is the force which acts between molecules at the surface of two bodies which are in contact with each other. It is a non-conservative force. We can use these to give the examples.

Complete step by step answer
As we know, friction always opposes a body’s motion. So, this can be both a necessity and a curse. Examples where friction acts as a friend can be seen in our daily life like vehicles moving on the road, humans walking on the road, writing on paper, lighting of matchsticks, assembling of machine parts and stopping of vehicles would be impossible without brakes. These things are possible because friction acts on the surface of contact.
Frictional force dissipates energy in the form of heat or noise which are non-recoverable. So, sometimes it acts as a foe. For example, heat dissipated because of friction can cause damage to machines. Friction also results in wear and tear of machines in the area of contact. A significant amount of fuel is required in machines, vehicles and engines to overcome friction.

Additional information
There are several methods to reduce friction like polishing, this reduces the interlocking and hence reduces friction due to irregular surfaces, lubrication, materials selection.

Note
Friction is a non-conservative force which means that it is dissipative in nature and once the energy is lost, it cannot be recovered. The work done against non-conservative forces are path dependent, that is it depends upon the starting and stopping point of the motion. Conservative forces are independent of path. For example, the electrical or gravitational forces are conservative in nature.