One way to think of energy is the ability to do harm. Things that are very dangerous possess considerable energy. With that definition in mind, the concept of kinetic energy can be motivated by considering the danger posed by moving objects. When a baseball is thrown by a child, it is not very frightening, though it can break a lamp. When a baseball is thrown by a major league pitcher, they can cause considerable injury. This contrast indicates that the energy of motion will depend on speed. Similarly, although a baseball thrown at 60 mph is dangerous, a car driving 60 mph is deadly. This contrast indicates that the energy of motion will depend upon mass.