How does something become charged using friction?

"Where friction or rubbing results in the transfer of electrons between particles, objects can become negatively or positively charged."

Explanation:

The motion resistance of one moving object with respect to another is called as "Friction". It isn't a basic force, like gravity or electromagnetism. Alternatively, scientists believe it is the product of the electromagnetic attraction in two touching surfaces between charged particles.

The friction have formula:  

Friction force (f )  = coefficient of friction  × normal force (N)

For an instances when one ride a bicycle, an example of rolling friction is the contact between the wheel and the way.

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the answer is c. the lower legs are levers, and the knees are fulcrums. the ankles hold the loads.