The Radiometer Composite Force Test

L. Thompson


I call the radiometer force a composite force as it includes the deceleration of the rarefied gas molecules to give the net acceleration of the vanes.  The test took place in a partial vacuum of 100 to 300 microns. A 60w halogen light was focused on various weight aluminum strips with carbon black on one side. The strips were holed to move on a horizontal rod. The weightier strips would show a little movement and would then bind on the rod (a frustration on my part). Yet an approximately 0.002 gm strip, holed on one end to hang on the rod, moved first with agitation and then energetically around and along the rod. 

Though a small mass, I found the centrifugal motion could  also have a non centrifugal  movement as in William Crookes original observations.   

The radiometer vanes and harness weigh substantially more than the small carbon blacked strip, leading me to think that other ways to apply the force could  be possible.

With limited equipment I did not take the test further.  Further study/testing would confirm my  initial observations. Then the study  could include the energizing and the deceleration phase of the  gas molecules.  It could explore the implied high molecular velocities in the "creep effects" across the vane surfaces. It would ask: why is there  little apparent offsetting force in the vane acceleration. It would quantify as what appears to me as the high efficiency of the transfer of molecular energy momentum to macro vane momentum. 

 2016/17 Test Proposal

I am proposing, via fixed internal surfaces, to transfer the composite force to the rotation of the radiometer bulb itself. This demonstration could be in a vacuum chamber using a lightweight bulb vented to the same partial vacuum, well balanced, and with pivot points at each end. 

The radiometer is in effect a momentum pump until a new equilibrium would be reached. If necessary, "kick start" the bulb rotation to a measured RPM. Measure the time for rotation to cease.  Then starting with the same measured RPM, compare after the input of energy upon the rotating bulb/vanes with the time lapse for the rotation to again cease. I anticipate a contribution from the internal application of the net force would now increase the rotation time.

And/or proceed to this test. Using a heavier weight completely closed cylinder for increased vane surface, proceed as above, using the closed cylinder as it own partial vacuum chamber. This test is to take place outside of the vacuum chamber and under a full atmosphere.  

The objective of this composite force testing is to show the force could also be directed outward.

I would like this recent proposal to take place by those who can become familiar with the radiometer, with vacuum experience, and with glass blowing experience. May 2, 2016