Re: Classical physics problem - for fun


"Edward Green" <spamspamspam3@xxxxxxxxxxx> wrote in message
news:1155698864.202561.318910@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Ron Baker, Pluralitas! wrote:

Assuming the voids are filled with a gas of less density
than the fluid but approximately the same pressure
and the gas and fluid do not disolve in each other:
Imagine slicing a plane containing
the centers of the two bubbles and imagine the graviational
potential energy represented as a surface above that plane.
The bubbles would lift the potential energy. Between the
bubble the potential energy would be higher (than at some
infinite distance). The fluid between the bubbles at that
higher energy is going to want to flow away to lower energy
regions. So the bubbles should move toward each other.

We finally reach the same conclusion, but I don't see how you
offhandedly knew that the bubbles lift the potential energy. What were
your intermediate thoughts?


Well, the bubbles don't actually lift the potential.
They just don't depress it like the massive fluid does.
Consider a discrete mass. It engenders a potential
well (with inverse quadratic sloped sides). You've probably
heard the analogy of the rubber *** as a model of
a potential energy surface. Distribute mass over the ***
according to the problem statement. In the voids there
is nothing to pull down the ***. Between the voids
there is less nearby mass pulling the *** down than far far away.

--
rb




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