Question

When the cutting edge of a knife is put against a fast rotating stone to sharpen it, sparks are seen to fly. Explain the reason.

Answer 1

When we sharpen a knife by putting it against a fast rotating stone, a huge amount of heat is generated in form of sparks due to friction between the cutting edge of the knife and the rotating stone.
Explanation:

1. When two bodies having irregular surfaces slides on each other there will be a force that opposes the relative motion known as friction.
2. Now more the irregular or rough the surfaces are, the more will be the friction.
3. Now when the cutting edge of the knife and the rotating stone come into contact (i.e.When we try to sharpen the knife), due to the friction the temperature of the knife and the rotating stone increase, and a huge amount of heat is produced and we can see it in form of sparks.
4. Now if the speed of the rotating stone increases, the heat produced also increases resulting formation of more sparks.