four rugby players are fighting to gain possession of the ball. The horizontal forces they apply to the ball are 167N north, 152N east, 135N south, and 149N west. The force of gravity and the normal force exerted on the ball are equal in magnitude

Ithink the answer is c. make unnecessarily  wide gestures 

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