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: pinwheel (was Re: electrostatic motor)



At 10:36 AM 5/22/00 -0400, Richard Berg wrote:

1. Apparently everyone agrees that this is not a Hero's engine using
electrons, the first myth.

Certainly not electrons alone.

2. Now the second one, electrostatic repulsion, I still have a problem
with. According to my order-of-magnitude calculations, there is more than
enough force to propel the rotator if you assume that the charges on the
propeller tip and the charge cloud are about equal, that the charging
occurs in about one millisecond,

One millisecond? Where does that come from? Why should it be relevant?

and the range is limited to about one millimeter.

One millimeter? Where does that come from? Why should it be relevant?

I would further assume that the charge dissipates about as
fast as it develops, spreading the charge out to where it is beyond the
range at which the force is significant, but nevertheless creating a
Coulomb force in the process.

I don't think I would assume that.

What does "dissipate" mean? I imagine a steady stream of + ions moving one
way and - ions moving the other way. Once the + guys are separated from
the - guys there is nothing for anybody to recombine with, so the amount of
negative charge is thereafter conserved by itself, and the amount of
positive charge is conserved by itself, until the ions terminate their
travels on the pinwheel or on the vdG terminal respectively.

In this case, the electrons from the tip attach themselves to atoms in the
air adjacent to the tip, forming a relatively heavy charge cloud that
assumes the reaction force and quickly scatters.

I don't know what that means.

I assume "electrons" is shorthand for "negative ions". There won't be very
many free electrons.

a. This clearly is an atomic effect (not molecular) because it works in
helium, according to Wolfgang.

Right.

b. No doubt there is a non-linear electric field involved - in fact, the
inverse square field is non-linear. There is a very large field at the
point. However, I do not understand how the breakup of atoms with one
being pulled toward the point can transfer momentum to the rotator. The
rotator must be the large object that ultimately assumes the reaction
force for that part or atom (or ion) that is attracted to the tip,
hits the tip, and thus presumably causes the whirlygig to rotate.

Actually, in the limit of a low-density gas, the ions that hit the tip
don't count. To a first approximation, those ions only transfer to the tip
momentum that they got by interacting with the tip's electric field, so
it's a break-even proposition. It's like the proverbial sailor who blows
on his own sail with an on-board fan.

It's the momentum carried off in the _other_ ions (the ones that are
created and sent off to land on the vdG terminal) that do the work.

To a second approximation the foregoing is complicated by the fluid
dynamics of ions moving through the air, but the basic idea is unchanged.

There is an experiment where you throw balls off the rotating chair at
an arms length, causing the chair to rotate.

Right; good analogy.

This whirlygig explanation
seems to me to be more akin to using one of these paddle balls with a long
rubber band: you are causing the attraction, which is opposite to the
force that occurs when the ball comes back to hit the paddle, yielding a
net effect of zero.

No, the fact that a current flows means that the balls are not returning to
the paddle.