Sliding friction and static friction are two types of friction that occur between two surfaces in contact. The main difference between them lies in the relative motion of the surfaces.

Static friction is the frictional force that acts between two surfaces when they are at rest relative to each other. It prevents the surfaces from sliding past each other. Sliding friction, on the other hand, occurs when the surfaces are in motion relative to each other.

The reason why sliding friction is generally less than static friction can be explained by the microscopic interactions between the surfaces. When two surfaces are in contact, there are irregularities and microscopic bumps and valleys on their surfaces. These irregularities create contact points between the surfaces.

In the case of static friction, the surfaces are not moving relative to each other, and the contact points between them have a chance to settle into a state of maximum interlocking. This interlocking occurs due to the attractive forces between the molecules at the contact points. As a result, static friction can be stronger because the interlocking of the contact points requires additional force to overcome.

When an external force is applied to overcome static friction and set the surfaces in motion, the interlocking between the contact points is broken, and sliding friction comes into play. In the sliding state, the contact points are constantly being broken and re-established as the surfaces move relative to each other. The interlocking is not as strong or stable as in the static case, resulting in a lower resistance to motion. Therefore, sliding friction is generally lower than static friction.

It’s worth noting that the magnitude of both static friction and sliding friction depends on several factors, including the nature of the surfaces, the applied force, and the presence of any lubricants or contaminants. These factors can influence the roughness of the surfaces, the adhesion between them, and the overall frictional behavior.