The statement that "the coefficient of static friction always equals the coefficient of kinetic friction" is not correct. In general, the coefficient of static friction (μs) and the coefficient of kinetic friction (μk) are different values.
The coefficient of static friction refers to the frictional force acting between two surfaces when they are at rest relative to each other. It represents the maximum amount of friction that can be generated to prevent the objects from moving. The coefficient of static friction is typically denoted as μs and can vary depending on the nature of the materials in contact.
On the other hand, the coefficient of kinetic friction refers to the frictional force acting between two surfaces when they are in relative motion. It represents the amount of friction experienced while the objects are sliding or moving against each other. The coefficient of kinetic friction is typically denoted as μk and can also vary depending on the materials involved.
In many cases, the coefficient of static friction is larger than the coefficient of kinetic friction for a given pair of surfaces. This difference is due to factors like surface roughness, adhesion, and interlocking between the surfaces when they are at rest. Once the objects overcome the static friction and start moving, the frictional forces reduce, and the kinetic friction comes into play.
It's important to note that the specific values of μs and μk can be determined through experimental measurements for different material combinations. The coefficients of friction are not always equal and can vary significantly depending on the nature of the surfaces in contact.