Basic Ideas: Energy can be neither created nor destroyed, but it can be converted from one form to another and it can be transferred from one object to another.
During a collision, energy is usually transfered from one object to another.
Energy can be stored in an object by lifting the object to a certain height. This energy is called gravitational potential energy. The gravitational potential energy of an object depends on how heavy the object is and how high it is. The heavier an object is, the more gravitational potential energy it has, and the higher an object is, the more gravitational potential energy it has.