"DAVID WILLIAMS" bravely wrote to "MIKE ROSS" (06 Jun
05  21:49:36)
 --- on the heady topic of "Pnu 732"

 -> it isn't very great but it's still something.
 ->

 DW> Yes. If the device is radiating energy asymetrically, then there will
 DW> be some (tiny) reaction force.
 DW>
 DW> However, in most vacuum tubes, the basic design is cylindrical, with
 DW> the heated cathode running down the axis, then the various "grids"
 DW> suspended cylindrically around it, and the anode "plate" around the
 DW> outside. Such a device would radiate energy pretty well symetrically,
 DW> so it wouldn't produce a significant reaction force.

Assumption aside, a plate can just as easily be made in a semi-circle.


 DW> Just for the sake of argument, suppose the device radiates 10 watts,
 DW> all in one direction. So the force will be about 10/3e8, or 3e-8
 DW> newtons. If the mass is, say, 0.01 kg, this will produce an
 DW> acceleration of 3 micrometres per second-squared. After a day (about
 DW> 1e5 seconds), it will have picked up a speed of about 0.3 m/s, or
 DW> about  one foot per second. Hmmmm.... That's more than I would have
 DW> guessed.

Ion rockets can achieve escape velocities approaching 100Km/s at low
power. Deep Space 1's ion thruster could produce 90 milli-Newtons from
2.5KW of electric power or about 36 micro-Newton per watt. This
hypothetical vacuum tube by comparison would be only 3 nano-Newtons
per watt.

 M*i*k*e

... A cynic is what an idealist calls a realist - Humphry in Yes Minister
--- Blue Wave/DOS v2.30