[extropy-chat] unidirectional thrust

[Keith Henson]

At 02:28 PM 11/03/05 -0800, Hal Finney wrote:

>Personally I'm a big fan of conservation of momentum.

snip

Me too.  Also conservation of energy.

And unidirectional thrust, if it is not velocity dependent (and reference 
frames are supposed to all be the same) can be shown to violate the 
conservation of energy by a simple thought experiment.

Just suspend the gadget at the end of a long arm in a vacuum, let it 
accelerate to some arbitrary velocity such that you can lower a wheel with 
a generator (or tap the hub of the suspension system) and make more power 
than it takes to generate the thrust.

I am not opposed to unidirectional thrust devices, would love to see one 
(bought the Dean Drive patent from the PO when I was in high school) but 
folks really should be aware that it isn't just conservation of momentum 
that gets lost if you can make one.

Keith Henson