Final answer:
The coefficient of static friction is greater than the coefficient of kinetic friction because the friction force is higher when two surfaces are not moving relative to each other.
Step-by-step explanation:
The coefficient of static friction is generally greater than the coefficient of kinetic friction. This occurs because when two surfaces are stationary relative to each other, the frictional force between them is higher. Once motion begins, the opposing frictional force decreases, leading to a lower kinetic friction coefficient. This is illustrated by the fact that pushing an object initially requires more force to overcome static friction than to maintain movement against kinetic friction. For example, if a crate with a mass of 100 kg has a static friction coefficient of 0.45, you would need to apply more than 440 N to initiate movement. However, once the crate is moving, the kinetic friction coefficient might be 0.30, requiring only 290 N to maintain a constant speed.