What is friction?
Answer
Friction is the force that opposes the relative motion (or tendency of motion) between two surfaces in contact with each other.
The working
Definition
Friction is a contact force that acts along the surface and always opposes the relative motion or attempted motion between two touching surfaces.
Why it arises
No surface is perfectly smooth; the tiny irregularities of the two surfaces interlock, and this interlocking resists sliding.
Types
Static friction acts on a body at rest, sliding (kinetic) friction acts on a moving body, and rolling friction acts when a body rolls. Static friction is the largest and rolling the smallest.
Direction
Friction always acts opposite to the direction in which the body moves or tends to move, so it slows objects down and produces heat.
Uses vs harm
Friction lets us walk, write and brake, but it also wears out machine parts and wastes energy as heat, so it is reduced using lubricants and ball bearings.
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