Energy is the capacity of an object to transform the world which surrounds it. Its unit is the joule.

By moving, bodies have the capacity to transform their environment.  Think how by moving we are able to transport objects, bump into them, break them...  Carry out the following simulation:

LEARN::the velocity of a body gives it the capacity to transform its environment.  This capacity is its kinetic energy and it depends on the square of its velocity and its mass.