In a laboratory experiment on friction, a 135-N block resting on a rough horizontal table is pulled by a horizontal wire. The pull gradually increases until the block begins to move and continues to increase thereafter. Figure E5.26 shows a graph of the friction force on this block as a function of the pull. (a) Identify the regions of the graph where static friction and kinetic friction occur.

Video transcript

Hey everyone today, we're dealing with the problem. That applies our knowledge of static and kinetic friction. So we're being told that in an experiment where we're applying a horizontal force an object until it moves, and for some time after it starts moving. We're being we're pushing a 86 newton box that is placed on a rough horizontal bench and pushed by said horizontal force. The graph given shows the friction force on the box as a function of the push in what reasons of the graph the static and kinetic friction occur. So let's break this down. We know that static friction, static friction acts on objects at rest at rest. So what does this mean? Well, it means the static friction increases from zero to the maximum Force applied and is also equal to the applied force from zero Newtons all the way up until the force is equal to the maximum force. Using these two aspects of static friction, we can say that static friction and let's write this in blue acts on the box from F is equal to zero. The force applied to zero all the way until The force equal to 45. Excuse ME, Newtons. So, from this stretch right here, all the way from point A to point B to F. Max. Now, kinetic friction on the other hand, let's write that here, kinetic friction acts on moving objects. As the name implies kinetic friction acts on moving objects moving it is a constant and it is less than F max. Its point of action is marked by a sharp decrease in friction force, which means that using these aspects of kinetic friction, we can say that kinetic friction acts and F Is created then 45 newtons. So this aligns with answer choice. C static friction occurs when the forces from zero all the way until F max 45 newtons, And kinetic friction occurs when it is greater than 45 newtons. I hope this helps, and I look forward to seeing you all in the next one.