Element to set the principle of the energy and work for two objects or systems. In case of problems involving an element Center, it is assumed that events occur in a horizontal plane, so the gravitational potential energy is not taken into account. Nor does it take into account for the case of the explosion of a projectile. Since it is considered the state an instant before the explosion and the state an instant after it.
|System i:||A System or Object that represent the initial state.|
|System f:||A System or Object that represent the final state.|
|W:||The work involved in changing state.|