In the story I'm writing, magic mostly works by mages moving energy from one place to another, or converting it from one type to another. One particular mage is naturally telekinetic—she doesn't have to do all the calculations (mass of the object, how much energy do we need to move it, etc.) in her head to move stuff around like other mages do. She also doesn't need to think about where she gets the energy for her telekinesis; she instinctively uses the pressure from the ground beneath her.
If this mage draws kinetic energy from a semisphere of ground beneath her that's three meters in radius, about how much energy does she have at her command at any given time? Since I don't actually know any physics, I don't know how to do this math, but I would guess it would involve taking the average mass of a piece of ground that size, and plugging it into Newton's law of gravity, correct?
Also, what happens to the ground after this mage takes energy from it? Does the temporary removal of its downward acceleration make it rise up, or is there no perceptible change?