Question

Explain why sliding friction is less than static friction?

Answer 1

Hint: We will understand what both of these terms mean and then we will move on to explanation of the question part. For the idea of the reader as the name implies, sliding friction is something related to sliding between an object and the surface and so is the static friction but in terms of state of rest prior to movement. We will explain that further.
Complete step by step answer: Let’s start with friction and then we will classify whether a friction is sliding or static. Whenever a body moves or tends to move over the surface of another body, an opposing force comes in to play tangentially between the two surfaces in contact and opposes any relative motion between them. This opposing force is known as friction. The causes of friction include, the phenomenon of inter-blocking between the two surfaces in contact and the adhesive force among the molecules of two surfaces in contact. Now, friction can be sliding friction, rolling friction, fluid friction etc. We will discuss sliding friction only. The opposing force that comes into play between two surfaces in contact when a body slides or tends to slide over the surface of another, is known as sliding friction. On the other hand static friction is the opposing force when a body is at rest over a surface, or the friction which exists between the two surfaces just before it shows any tendency to move. In simple terms we might say that the friction when the object is already in motion over a surface is called sliding friction and the friction that exists between these surfaces when the body is at rest, is called static friction. In sliding, the time for interlocking between the body and the surface is very small, so interlocking is not that strong. That is less force is required to overcome this interlocking. On the other hand if we need to overcome the interlocking when the body is at rest, we will be required to apply more force. Because of this reason, sliding friction is always less than static friction.

Note: Friction is a consequence of Newton’s third law of motion, which says every applied force has the same amount of force opposing it in the opposite direction of the mother force. Sometimes you might get questions like, units for friction or dimensional formula for friction, well it is the same as that of force.