Lawrence is conducting an experiment to see how much force it takes to push objects made of different materials along the ground. he uses a rubber object, a plastic object, a wooden object, and a glass object. he makes sure that each object is the same mass and that each object has the same amount of surface area in contact with the ground. he decides to test his objects on the same patch of cement under identical conditions for each trial. which of these are constants in lawrence's experiment? the amount of force he uses to push each object the amount of surface area contacting the ground for each object the type of surface he pushes each object along the material each object is made out of the mass of each object