Final answer:
The coefficients of friction depend on the two surfaces in contact and can vary greatly. In general, the coefficients of kinetic friction are less than the static counterparts. Friction opposes motion and acts opposite to the direction of motion, parallel to the surface, and perpendicular to the normal force.
Step-by-step explanation:
The coefficients of friction can vary greatly depending on the two surfaces that are in contact. The values of friction coefficients are represented by symbols such as Mk (kinetic friction) and Ms (static friction). In Table 5.1, it is observed that the coefficients of kinetic friction are generally less than their static counterparts.
Friction is a force that opposes the motion between two objects in contact. It always acts opposite to the direction of motion, parallel to the surface between the objects, and perpendicular to the normal force. The magnitude of friction depends on factors such as the normal force, the type of materials in contact, and whether the object is at rest or in motion.
For example, in the case of a crate with a mass of 100 kg and a coefficient of static friction of 0.45, a force parallel to the floor greater than 440 N would be required to overcome static friction and move the crate. Once the crate is in motion, the force needed to maintain constant speed is less, typically represented by the coefficient of kinetic friction (0.30 in this example) multiplied by the normal force.