Differentiate between static and dynamic friction.

Static friction is the force that prevents an object from starting to move, while dynamic friction is the force that resists its motion.

Static friction, also known as starting or limiting friction, is the frictional force that must be overcome to set an object at rest into motion. It acts when an object is stationary and opposes the force that attempts to make it move. The magnitude of static friction varies depending on the applied force, but it has a maximum limit. This maximum limit is determined by the nature of the surfaces in contact and the normal force acting on them. When the applied force exceeds this limit, the object starts to move, and static friction ceases to act.

On the other hand, dynamic friction, also known as kinetic or sliding friction, is the frictional force that acts on an object that is already in motion. It opposes the direction of motion and tries to slow down or stop the moving object. Unlike static friction, dynamic friction does not change with the applied force. It remains constant as long as the object is in motion and the nature of the surfaces and the normal force remain the same.

The key difference between static and dynamic friction lies in their roles and behaviours. Static friction prevents motion and changes according to the applied force until a maximum limit, while dynamic friction resists motion and remains constant during the motion.

In practical applications, understanding the difference between static and dynamic friction is crucial. For instance, in vehicle design, engineers need to consider static friction for tyre grip when a vehicle starts moving, and dynamic friction for braking and controlling the vehicle when it is in motion. Similarly, in sports like football or cricket, players need to understand these frictional forces to control the ball effectively.

In summary, both static and dynamic friction are fundamental concepts in physics that describe the forces that oppose motion. However, they act under different conditions and exhibit different characteristics.