Question

when a fire stone is rubbed on a hard and ruff surface we get fire. this is

Answer 1

When a fire stone is rubbed on a hard and rough surface we get fire. This is due to friction.

The act of rubbing produces friction. The intensity of the friction is directly proportional to the roughness of the surfaces which are being rubbed against each other. So if the roughness of the surfaces increases, friction increases and more heat is generated.

Answer 2

When a stone is rubbed on a hard or rough surface, a force called friction is produced between the stone and the surface due to which we get fire. Friction is produced when we overcome the resistance of one object rubbed against another. This frictional force opposes the direction of motion of an object. If we simply place the stone on the rough surface, no friction is produced because there would be no resistance. It is produced only if we rub the stone on the rough surface.
Friction largely depends on the roughness of the surface. The more rough the surface, the more will be the force of friction and eventually more fire is produced.