[Phys-L] Re: World Jump Day

[John Denker <jsd@AV8N.COM>]

Anthony Lapinski wrote:
> > The idea is for people on Earth to simultaneously jump

It's much more impressive if the jump NON-simultaneously.
   a) Imagine rows of people, with successive rows jumping at successive
    times, phase-matched to the surface-acoustic-wave velocity.  This
    launches a plane wave.  Given N jumpers, the amplitude grows like N,
    and the energy grows like N^2.
   b) Ditto for rings of people centered on some point "A", jumping
    at successive times, phase-matched to the inbound SAW.  This launches
    a circular wave, focussed on point "A".  Not only does the energy grow
    like N^2, more-or-less all of the energy is delivered to a single point.
    If you arrange the phases just right, this can _concentrate_ the energy
    by a considerable factor ... it's the D=2 analog of the sonoluminescence
    geometry.

Rick Tarara wrote:
> I've used this kind of idea for a test question in the past.  If all the
> Chinese started jogging to the East, what would happen to the length of a
> day?  Throw in some numbers--average mass and number of Chinese plus earth
> parameters, you can do it as a problem.

OK...

> Of course they have to keep jogging
> and not fall into the ocean!

It is more realistic to have them jog around in a big circle.
This is less effective than rectilinear jogging by a factor
that depends on the size of the circle ... but that's not zero.

It can be nicely treated as an addition-of-angular-momenta problem.
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