Which type of friction is usually highest when two surfaces are at rest?

Static friction is the type of friction that occurs between surfaces that are not in motion relative to each other. It acts to prevent the initiation of relative motion when a force is applied. This type of friction is typically the highest compared to other forms of friction because it must overcome the attractive forces between the surfaces at rest.

When two surfaces are still, static friction can increase up to a maximum threshold, known as the maximum static friction, which is determined by the nature of the surfaces and the forces pressing them together. Once the applied force exceeds this maximum static friction, the surfaces will begin to move relative to each other, at which point kinetic friction takes over.

Kinetic friction, dynamic friction, and rolling friction are all lower than static friction because they act on surfaces that are already in motion. This key characteristic of static friction helps in understanding various applications in manufacturing and engineering, where starting motion is often more challenging than maintaining it.