Investigate the attractive forces of gravity and show that these attractive forces depend on the mass of the interacting objects.  In the first part of the experiment, students depict gravity using the concept of gravity wells, which visually show the pull or depth of gravity that an object exerts in space.  In the second part of the experiment, students will investigate how the mass and size of objects falling to the earth due to gravity can affect the depth and size of a crater.  Using the equation for force, F=MA, students will demonstrate using calculations that force is proportional to the mass of the objects.