Sliding friction is less than static friction because static friction involves the microscopic interlocking of the irregularities between two surfaces when they are at rest. These irregularities have time to settle and interlock tightly, creating a stronger resistance to the start of motion. In contrast, once the object is sliding, the surfaces do not remain in close contact long enough for these irregularities to interlock as effectively. The relative motion breaks the interlocks, reducing the frictional force. Therefore, sliding friction is smaller since fewer points resist the motion compared to static friction.
