Later , applied force , Fa = F , then fs also increases but only up to a certain limit . As soon as Fa becomes greater than fs , the ball starts to move .
fs acts when a body is at rest . Hence called Static friction o
fs max ∝ N
Limiting value of fs depends on Normal reaction , and is independent of the area of contact
fs max = constant * N
fs max = μs N where μs is the coefficient of static friction This coefficient depends on the nature of surfaces in contact . o
According to the Law of Static friction , Static friction is always less than or equal to the limiting value of fs
fs =< fs max
fs max = μs N
fs =< μs N