Make sure your hands are dry. Rub them together briskly so that you create a lot friction. Observe the heat in your hands. Now add some hand lotion and rub them again. What happened this time? Note your finding on A4 size sheet and write down why friction is considered necessary evil.

Dear Student

When some hand lotion is added to hands and rubbed then not much heat is produced in hands as now hands are smooth surface due to lotion and hence less friction is there.
 

Friction is a necessity:

• It is because of the friction between the ground and our feet that we are able to walk
• The brakes of a vehicle cannot work without friction
• In the absence of friction, it will not be possible to write on a paper with a pencil

Friction is an evil:

• It causes wear and tear of machinery
• A large amount of power is wasted in overcoming friction and the efficiency of the machines decreases
• Excessive friction between rotating parts of a machine produce enough heat and causes damage to the machinery.

As friction has both advantages and disadvantages, we can say that friction is a necessary evil.

Regards