[D-fendr]

Consider the example of picking up a rock from Earth, taking it in a spacecraft to a planet much more massive than Earth, outside the Solar System, and then dropping it near where this particular planet can begin to attract this rock towards itself.

I think I'm going to show my ignorance here. Does this mean potential energy is completely quantified by gravitation and mass?

What if you transport a massive rock to a weightless environment? Have you decreased its potential energy? Wouldn't this violate conservation of energy?

[James C. Bennett]

I used that example of taking a rock from one planet to another to show that the contained potential energy cannot be determined.

[TXnMA]

I believe your problem is that you are trying to perceive potential energy as a stand-alone property. It is not; potential energy is a delta.

Potential energy must always be calculated or stated with respect to some "ground" reference. In the water column I mentioned, the measured pressure was between the "head" (height) of the column and its "bottom" -- with such variables as the height of the column, G, density, etc. left unstated.

And, of course, potential is not confined to gravitational effects. In order to operate, even good old Ohm's Law ("E = IR") requires an (often unstated) "ground potential" to provide a reference for the electromotive (potential) force, "E".

I have to chuckle when I think of the Potential -to- Kinetic conversions on my Fuji-san" trek. I just realized that I had been unconsciously using as my "ground", Station 7(?) -- which we had climbed past early the night before on our climb to be at the summit for sunrise [spectacular!]. Why? It was at that station where we reached the bottom of our exhilarating "flying" descent down the (~45 degree) cinder slope -- and dumped the cinders from our (by then well-worn) boots -- before returning to the trail for the rest of the plod down to the bus station.

(My potential energy at the summit was obviously less WRT Station 7 than it was WRT the bus station -- but the former "delta " was certainly the most fun!

"Proper" "ash-slide" descent technique entails leaning back onto your "Fuji-stick" (climbing stick) and using it as stabilizer, tiller, and brake as you "skate" long "seven-league boot" steps under the (dramatically obvious) influence of gravity. As a measure of some of the expended energy, my Fuji-stick" was nearly six inches shorter when we reached Station 7 (as measured against a new one)! '-)

I "leave as an exercise for the student" the calculation of my potential energy between the summit of Fuji-san and our home on the Kanto Plain -- slightly above sea level... '-)

~~~~~~~~~~~

All this discussion of transfers and expenditures of energy brings to mind the old Japanese saying,

"He who fails to climb Fuji-san in his lifetime is a fool."

"He who climbs it twice is twice a fool..."

~~~~~~~~~~~

'-)