Equilibrium on a Rough Horizontal Plane

Applied Mathematics — Second Secondary

The force of friction

Friction is a force that arises between two surfaces in contact, and acts in the direction opposite to the motion or to the tendency to move.
If we try to drag a box on a rough floor, friction opposes this attempt, and the box does not move unless the applied force exceeds the maximum friction.
When the body is at rest, the friction is called static friction.
It is a variable force: its value equals the applied force exactly, as long as that value is less than the maximum.
When the body is about to move, friction reaches its greatest value, called the limiting static friction.

Comparison aspect	Main idea	Keywords
In equilibrium	F ≤ μs R
At the limit (the body is about to move)	F = μs R
•	Here R is the normal reaction and μ_s is the coefficient of static friction, a number without units that depends on the nature of the two surfaces.	Herenormalreactioncoefficient

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