The discussion revolves around the behavior of gravitational potential energy (U) and kinetic energy (K) as a mass is moved away from Earth. Participants explore the implications of gravitational energy in large-scale contexts and whether gravity can be considered a conservative field.
Participants express differing views on whether gravity is a conservative field and how potential energy behaves at large distances. There is no consensus on these points, and the discussion remains unresolved.
Participants highlight the dependence of potential energy on the chosen reference point and the implications of external forces on energy conservation, but these aspects remain complex and not fully resolved.
Realize, since we take U = 0 at infinity as the reference point, that the U of the system starts out negative and increases to zero.Ignition said:If a mass became pulled up from Earth, its U increases and its K decreases, but if it became pulled into space, its U becames 0.
Not sure why you'd conclude that gravity is not conservative at large scale. Realize that the sign of potential energy depends on your reference point.So, could we say that Gravity is not a conservative field in large scale, but a negative Energy?
Well, no. If it is pulled into space, then there is a force acting on it which would increase its total energy. It might well keep the same K (Kinetic energy) while increasing its potential energy. If it already has a large kinetic energy on Earth and uses only that energy to move away from the earth, with no external force, then the kinetic energy decreases while the potential energy increases so the total energy remains the same.Ignition said:If a mass became pulled up from Earth, its U increases and its K decreases
Again, no. Its potential energy does NOT become 0 "in space". For gravitational problems, potential energy (which, as Doc Al said, is always relative to some reference point) is taken to be 0 at infinity, not just in space. If you take an object to have a very large negative potential energy on Earth (and considering only the Earth's gravity) the at several light years from the Earth it would have a very small, but still non-zero negative, potential energy., but if it became pulled into space, its U becames 0.So, could we say that Gravity is not a conservative field in large scale, but a negative Energy?