The discussion centers on the behavior of gravitational potential energy (U) and kinetic energy (K) when a mass is moved from Earth to space. It is established that as a mass is pulled up from Earth, its potential energy increases while its kinetic energy decreases. The participants clarify that gravitational potential energy is relative to a reference point, typically taken as zero at infinity, and that gravity remains a conservative field despite the changes in energy states. The conclusion emphasizes that potential energy does not become zero in space but approaches zero as the distance from Earth increases.
PREREQUISITESStudents of physics, educators teaching classical mechanics, and anyone interested in the principles of energy conservation and gravitational forces.
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?