Re: Engineering Newsletter

[Kevin C Houston <hous0042@maroon.tc.umn.edu>]

On Sat, 25 Nov 1995, Steve VanDevender wrote:

> Kevin C. Houston writes:
>  > To: all nitpickers
>  > From: A nit(wit) who is tired of getting picked on.  ;)
> 
> Sorry, but conservation of energy and momentum are too
> fundamental to ignore.  If you can't follow those rules then you
> may as well give up and design a warp drive, since you're
> throwing out the laws of physics anyway.

Would if I could, but I can't, so I won't.

> 
>  > see my web page
>  > http://www.umn.edu/nlhome/m056/hous0042/asimov.html
>  > for an idea that is consistant with Steve and Timothy's objections.
>  > 
>  > i.e. reflection transferrs momentum to the normal, and absorbtion 
>  > transfers momentum in the direction of the photons original vector.
>  > 
>  > Advance billing: it is _still_ possible to cancel the momentum within the 
>  > structure of the antenna/sail .
>  > 
>  > HA!
> 
> We'll see.  You must either absorb the photon and thereby absorb
> its momentum, or reflect the photon and get momentum to balance
> the change in direction of the photon.  The only way to not get
> any momentum change is to either not interact with the photon or
> reflect it so as to leave it travelling in the same direction it
> came with the same energy.
> 

no,  first the photon is reflected at an angle,  this dumps some of the 
momentum into the perpendicular directionthe photon leaves the first sail 
element (reflection) and is absorbed in the second, inner element.  as 
far as that element is concerned, the photon came from the _front_ of the 
ship.

> If the system consisting of the photon beam and the spaceship
> plus sail assembly doesn't have the same momentum after the
> interaction as before, then you'll have to go back to the drawing
> board.  Perhaps after a brief refresher course in physics.
> 

it does have the same momentum, just that some of that momentum has been 
made to cancel out.  equal but opposite momentums cancel out