Sir Isaac Newton's second law of motion states that the force exerted by a moving object is equal to its mass times its acceleration in the direction from which it is pushed, stated as the formula F=ma. Because force is proportionate to mass and acceleration, doubling either the mass or acceleration while leaving the other constant will achieve half the force of impact, and the force of an impact increases when an object of a constant weight is accelerated to higher speeds. Several different experiments can be constructed that demonstrate this principle.
Collect a rock and a wadded up piece of paper. Because gravity's acceleration is a constant, all objects fall at the same rate regardless of their mass. Test this law by dropping both items simultaneously and watching them fall at the same speed. Now place a bowl filled with powdered sugar or flour underneath the rock, and drop it from a fixed height into the powder. Set the bowl to the side, being careful not to disturb the powder in it. Drop the ball of paper from the same height into a bowl with the same amount of the same powder. Compare the craters in the powder created by each impact. Because acceleration was constant, the difference in size between the crater made by the rock and the one made by the paper illustrates that an increase in mass directly increases the force of the impact into the flour.
Screw an eyelet into a softball and another into the lintel of a door frame. Hang the softball from the door frame by a piece of string tied through the eyelets so that it hangs a few centimeters above the floor. Mark the spot directly underneath the softball's resting position. Move the hanging softball and place another softball on the marked spot. Pull the hanging softball back so it is three feet from the ground and release it so it swings and hits the softball on the floor. Measure the distance the softball on the floor travels. Repeat the experiment, substituting a plastic Wiffle ball for the softball on the floor, and measure the length it travels after impact. This experiment illustrates that that when force is held constant, the acceleration is greater in objects with less mass.
Hot Wheels Experiment
Construct a simple ramp that's 18 inches high and about 24 inches long using a piece of thin plywood and bricks. Place a toy car at the top of the ramp. Release it and measure how far it rolls. Tape two metal washers to the car, release it from the ramp and measure how far it rolls. Repeat the experiment with five washers taped to the top of the car. This experiment shows that as mass increases with gravity's constant acceleration, the force pushing the car along the floor increases, making heavier cars travel farther.