what is the only force that can act on an object in free fall? gravity friction air resistance speed; increasing which factor will cause the gravitational force between two objects to decrease?; what determines the strength of the gravitational force of an object in space; what are the units of mass and weight; which factors affect the gravitational force between two objects select all that apply; if siobhan hits a 0.25 kg volleyball with 0.5 n of force, what is the acceleration of the ball? m/s2; what is the weight, on earth, of a book with a mass of 1.5 kg? 1.5 n 6.5 n 11.3 n 14.7 n