Universal Solvent (Spoilers!)

Wilmer Rivers rivers at seismo.CSS.GOV
Tue Apr 4 16:00:37 CEST 1995


Jon Cato Lorentzen <jonlo at ifi.uio.no> warns:
> Non-Scandinavian readers beware... SPOILERS AHEAD!
and I herein reinforce this warning!!!




Jon argues that once the Ducks have reached the hollowed-out room
at the center of the earth, Scrooge would not fall out and then yo-yo
back and forth past the exact center, since in a hollow sphere the
gravitational potential is constant and its gradient (the gravita-
tional field) is therefore zero.  That would of course be true, but
the room is not empty!  The Universal Solvent itself rests at the
exact center of the spherical room, and (as you will recall from the
explanation of how it "dissolves" things) it has a mass equal to that
of some of the rock which it has swallowed up inside the hollow room.
Although the Solvent normally extrudes what it swallows, the very last
extruded material now keeps falling back into the blob of Solvent that
lies at the center of the room, and it gets re-absorbed.  So this blob
of liquid has a mass equal to that of a significant chunk of rock,
and this is why Scrooge falls towards it (and back towards it again,
after passing it).  We must assume that the mass of rock within the
Solvent is not **too** big, however, since ...

Mild Spoiler for Part 3 follows!

Scrooge is able to return it to the surface still inside the jar.
This is OK, since the Solvent needs to contain only a small amount
of mass in order to pull Scrooge back and forth; after all, as you
point out, all the other gravitational forces cancel, so the little
bit of rock held within the Solvent will suffice to make Scrooge
fall towards it.

Anyway, thanks for taking the physics so seriously!  I wish someone
would take up the torch passed by Tony Strobl and come up with a
new comic to start kids thinking about science: "Donald Duck in
Physics-Magic Land", or something.  Former engineer Don Rosa, are
you listening?

Regards,
Wilmer Rivers




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