What does a coefficient of friction depend on? What does a coefficient of friction not depend on?

Question

BlackTom AI · Accepted Answer

To approach this question, I’ll evaluate what the coefficient of friction (mu) actually depends on and what it does not depend on.
Option a: 'It depends on the contact surfaces, it does not depend on the area of contact.' This is correct in physics: mu is determined by the materials and surface textures in contact, not by how large the contact patch is. The frictional force is F = mu * N, where N is the normal force, and N is essentially the weight for a horizontal surface; increasing the contact area does not change mu or the friction force in the ideal case. So, this option captures the standard dependency correctly.
Option b: 'It depends on the object’s weight, it does not depend on the object’s size.' This is misleading. While the friction force F = mu * N can change with the normal force N (which is related to weight on a horizontal plane), the coefficient mu itself does not depend on weight. The statement confuses the friction force with the coefficient and incorrectly ties mu to weight.
Option c: 'It depends on the object’s size, it does not depend on the object’s weight.' The size of the object (dimensions or volume) does not determine mu; mu is a property of the contacting materials. The claim about weight is also problematic for the same reason as in option b, making this option inaccurate.
Option d: 'It depends on the area of contact, it does not depend on the surfaces.' This is false because mu is not a function of contact area. In idealized dry friction, area cancels out in the friction equation F = mu * N, so larger contact areas do not change mu. Moreover, mu fundamentally depends on the surface materials, not the area.
Overall, the reasoning shows that the correct conceptual takeaway is that the coefficient of friction depends on the contact surfaces (materials and texture) and is independent of the contact area, aligning with option a.

What does a coefficient of friction depend on? What does a coefficient of friction not depend on?单项选择题

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