get it? 3. describe the source of friction.

Brief Explanations:

Friction is caused by the irregularities on the surfaces of two objects in contact. At a microscopic level, these surfaces have bumps and valleys that interlock when the objects move relative to each other. Also, attractive forces between the molecules of the two surfaces contribute to friction.

Answer:

Friction is due to surface - irregularities and intermolecular forces between two contacting surfaces.