FUNDAMENTALS ...............................................
Energy in a Collision

Imagine throwing a ball against a wall as hard as you can. What will happen when it hits the wall?

 Everyone knows that it will bounce back! Right? Anything in motion has kinetic energy---energy of motion. The kinetic energy of the moving ball is converted to potential energy as the ball is squashed into the wall. This potential energy becomes kinetic energy again as the ball springs back into shape and propels itself away from the wall.

The change in the direction of the ball is caused by the elastic nature of the ball itself. Much like a spring, the ball "squashed" itself against the wall then rebounds as it becomes round again.

Now imagine that the wall is moving and has its own kinetic energy. At the moment of collision, the wall transfers some of that energy to the ball.

 Now think about hitting a baseball from a tee. All of the energy in this system starts with the batter and is transferred to the bat. Some of the energy in the bat is then transferred to the ball causing it to fly off the tee. Hitting a baseball that is pitched involves more total energy. The ball has energy and the bat has energy.
Remember the energy that the ball has when you throw it against a wall? It has the same energy when it hits a bat. But a swinging bat adds energy too. The combined energies make hitting a home run easier when a baseball is pitched.

Why are most home runs hit off of fastballs?