Dynamic friction, also called kinetic friction, is the frictional force that opposes the relative motion or sliding between two surfaces in contact. It comes into play once an object is already in motion and is moving across another surface. Dynamic friction is a fundamental concept in physics and engineering and is essential for understanding the behavior of objects in motion and the forces that affect their movement. Dynamic friction is generally slightly lower than static friction for the same surfaces. This means that once an object is set in motion, it usually requires less force to maintain that motion than to initiate it from rest.
Dynamic friction is encountered in everyday situations, such as the rolling of a ball, the movement of vehicles on a road, or the sliding of objects across a table. It's an important consideration in designing mechanisms, calculating the force needed to keep objects moving, and understanding the energy requirements for maintaining motion.