Question

Which of the following statements is correct about friction?

• A. The coefficient of friction between a given pair of substances is largely independent of the area of contract between them.
• B. The frictional force can never exceed the reaction froce on the body from the support surface.
• C. Rolling friction is only slighting smaller than sliding friction.
• D. The main source of friction is the irregularity of the surface in contact.

Answer 1

Answer: (A)

The coefficient of friction between a given pair of substances is largely independent of the area of contract between them.

The coefficient of friction between a given pair of substances is independent of the area of contact between them. $\mu$ > 1 for copper on cast iron.
Rolling friction is much smaller than sliding friction.
Irregularly of the surfaces in contact is not a main contributor of friction.