Potential energy
Also called Stored energy
Energy stored in the arrangement of a system whose parts interact through conservative forces. It belongs to the configuration of the whole system rather than to any single object, and only changes in it are physically meaningful.
Potential energy belongs to an arrangement, not to an object. The AP Physics 1 CED is specific about this: a system composed of two or more objects has potential energy if the objects within that system only interact with each other through conservative forces. A system made of a single object can only have kinetic energy.
So the strict phrasing is that a ball held above the ground has no potential energy of its own. The ball and Earth system has it, by virtue of their separation. That sounds pedantic until a question asks which system's energy changed, at which point the answer depends entirely on where the boundary was drawn.
Three properties follow.
- It is a scalar quantity associated with the position of the objects within the system.
- The zero point is yours to pick. The CED calls the definition of zero potential energy a decision made by the observer to simplify or otherwise assist in the analysis, which is why only a change in ever survives into an answer.
- Potential energies are associated only with conservative forces. There is no friction potential energy, because the work friction does depends on the route taken.
For a system holding more than two objects, the total is the sum of the potential energy of each pair of objects within it.
The two forms AP Physics 1 works with are gravitational and elastic.