Question

Co-efficient of friction is a constant, isn't it? So how come it can change when the surfaces in contact don't change?

I'm asking this cz in a math question I found the following statement- "The co-efficient of friction when there is no motion is 0.5, but it drops to 0.4 when the table starts to move"

Answer 1

there are two type of friction static friction whose coefficiant is given 0.5 and another one is dynamic friction which is 0.4