Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: [Phys-l] authoritative gravitational potential energy



> .... define gravitational potential energy as the work done to
move an object from a very large distance away to a
> point in a gravitational field

The usual definition is the *negative* of the work done *by the gravitational force*. Using this corrected definition, it doesn't matter whether the object is at rest before and after.

Furthermore, there should be some mention of the idea that PE is only defined for a system that includes both interacting objects (and implicitly the field) and that in general, we need to sum up the negative gravitational work that each object does on the other. By summing up both, we get a result that is frame invariant, whereas the work done on just one object is not. (One therefore needs to be careful when computing escape speeds in moving frames, as for example when you simultaneously want to escape from both the sun *and* the earth. I have a recent article on this topic if anyone's interested: <http://usna.edu/Users/physics/mungan/Publications/WAS2.pdf>.)
--
Carl E Mungan, Assoc Prof of Physics 410-293-6680 (O) -3729 (F)
Naval Academy Stop 9c, 572C Holloway Rd, Annapolis MD 21402-5002
mailto:mungan@usna.edu http://usna.edu/Users/physics/mungan/