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 contact between them
• B. The frictional force can never exceed the reaction force on the body from the support surface
• C. Rolling friction is only slightly smaller than sliding friction
• D. The main source of friction is the irregularity of the surfaces in contact

Answer 1

Answer: (A)

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. Irregularity of the surfaces in contact is not a main contributor of friction.