Today in physics class we talked of Gravitational Potential Energy. We talked about how K1 + U1 = K2 + U2 etc etc. But the idea of potential energy makes no sense to me. They say if you lift something off of the ground I.E. a phone. If i lift the phone up and put it on a table, the energy I used to lift it up is turned into potential energy after it is at rest. And the potential energy of that will be released into Kinetic energy. But what IS potential energy. What exactly is it? What about my phone is changed when I sit it on the table except now it has 'potential energy'.