Why does time change
single 14 almost 15 and im a mom to a newborn

The objects are acted upon by only one force. gravity. mass times the acceleration of gravity (-9.81meters/second squared).

Answer(a)   the matererials that are in contact, the two materials and the nature of their surfaces/// (b)/// the force pushing the two surfaces together, pushing the surfaces together causes the more of the asperities to come together and increases the surface area in contact with each other