This would be an investigation of Newtons second law of motion, which basically goes like this: "The acceleration of a body is parallel and directly proportional to the net force and inversely proportional to the bodys mass". The formula for this law is F = ma, where F is the force, m is the mass, and a is the acceleration. What this law means is the more force there is, the more accleleration there is. It also means the more mass there is in the body, the less acceleration there is. When things have more mass, there is more weight generated by the force of gravity, and some of the acceleration is lost to other energy forms, such as heat and friction. What you want here is a demonstration of the direct relationship between the force applied and the acceleration that develops. So we keep the mass of the trolley the same, that would be the control variable. Lets use an inclined plane, with textbooks to calibrate the amount of incline. The sharper the incline, the more force will be generated. Run three separate trials, one with one textbook of elevation, one with two textbooks, and one with three textbooks. We should see a progressively higher acceleration as we increase the number of textbooks, which would demonstrate the direct relationship between force and acceleration.

**Further Reading**