Friction · घर्षण
A free Physics lesson for Class 8 children.
Friction is the force that opposes motion between two surfaces in contact. It acts in the direction opposite to the motion.
Friction is caused by the tiny bumps on surfaces. Rough surfaces have more friction than smooth ones.
Static friction stops a body from starting to move. Sliding friction acts once it moves, and is a little smaller.
Rolling friction is smaller than sliding friction. That is why wheels and ball bearings make moving easier.
Friction is a friend: we can walk, write and stop a vehicle because of it. It is also a foe: it wears out shoes and machine parts and wastes energy as heat.
Lubricants like oil and grease reduce friction. Fluids like air and water exert fluid friction, or drag, so vehicles are given streamlined shapes.