Friction
Physics · घर्षण · 13 facts
Friction: force opposing relative motion between two surfaces in contact
Caused by irregularities (roughness) of surfaces at microscopic level
Static friction > Kinetic friction > Rolling friction (in magnitude)
Static friction acts when object is stationary; prevents motion from starting
Kinetic/Sliding friction acts when object is already moving on surface
Rolling friction is least, hence wheels and ball bearings reduce friction
Friction depends on: nature of surfaces and normal force; NOT on area of contact
f = uN where u = coefficient of friction, N = normal force
Advantages of friction: walking, writing, braking, holding objects all need friction
Disadvantages: wear and tear of machines, heat production, energy loss
Lubricants (oil, grease) reduce friction; polishing surfaces also reduces it
Streamlined shapes reduce air/fluid friction (drag) in aircraft, cars, fish
Tyres have grooves/treads to increase friction for better grip on roads