Properties of the Radiometer Force

L. Thompson

Extensive literature is on the rarefied gas reactions of the radiometer. Yet, little attention seems given to the actual properties of the radiometer force. The purpose of the following testing is to show some of these properties.

The equipment used is a 1/2 hp vacuum pump. The vacuum chamber is 10 inches in diameter with 1/4" thick polycarbonate walls. A 60w halogen spot light projects light and radiant energy.  I am using a digital scale accurate to 0.01 gram. 1 radiometer vane weighs about 0.06g and the 4 vanes and harness weigh 0.6g. The smallest surface area used in the testing weighed about .002 gram (extrapolated from the weight of a larger surface area).  The units of vacuum measure are:  1/760 atmosphere = 1 torr.  1 torr = 1000 microns.

In the radiometer the application of a net force overcomes the inertia of the vanes and harness. I observe a small force is inputted, as in a "momentum pump", to increasing the momentum of a larger vane mass in which well balanced vanes can reach 2000 to 3000 RPM.

In atmospheres above 1000 +/- microns the crowding effects of the gas molecules prevent movement. In high vacuums in the micron range of 10+/- microns, pressure differentials are not present as the individual gas molecular spacing is too great for pressure differentials to work.

With the input of energy the vanes begin to show movement around 1000 microns. The testing is in the partial vacuum range of  100 to 300 microns. In this range the radiometer vanes and harness, when placed in the vacuum chamber as a control check, show a similar response as in the radiometer.

Many variables can be changed to increase or decrease the force exerted. These variables could be the interplay of heating, atomic weight of the rarefied gas, mass inertia, spacing and shape of the surfaces, type of materials, and degree of vacuum. 

Yet out of  the complexities presented in the radiometer is also simplicity. This simplicity is: the radiometer vanes spin in response to the input of energy or to the taking out of energy (the "refrigeration effect").  In the testing  I am using this simplicity to demonstrate the characteristics of the resulting force. I call this force a composite force because the transfer of molecular momentum also results in the deceleration of the individual rarefied gas molecules to then give the net macro acceleration of the vanes and harness.

Observations and Notes

A. In the radiometer the force results in centrifugal acceleration - as if the force needs to "push itself" into a lower pressure area. 

B. When the rarefied gas molecules transfer momentum/energy, the gas molecules are cooled, are decelerated. This cooling, simultaneously taking place with the transfer of molecular energy/momentum into macro momentum, would represent the "exhaust side" of the generated power.

C. The radiometer was broken at the base to let in air/oxygen. I applied a strong heat source (a 60w halogen)  to the vanes.  A cloud of smoke erupted.

Before breaking the sealing tube, the same energy source was applied. The vanes spun rapidly.  The spinning radiometer vanes, with the input of energy into momentum, were running cooler. There was also more time in the rotation itself to dissipate any excess heat as re-radiated energy. Then when the vacuum was released to a full atmosphere and the vanes could no longer rotate to run cooler, oxygen combustion took place.

D. In the testing the gas molecules are recharged and reused. There is no external exhaust. In effect with the input of energy, the gas molecules are trapped to do work and to be reused with the input of energy.

E. I would like to give some thought to radiant energy in dispelling excess energy. A testing surprise  was that with the strong input of energy, the vanes first spin clockwise then upon cooling the vanes spin in the opposite, counter clockwise direction. This could be due to radiant energy radiating at a faster rate from the carbon black surface- thus creating an opposite pressure differential.  (This is likely the the refrigeration effect when the radiometer is first taken out of a refrigerator.) 

F. I feel the initial energizing of the gas molecules could involve Newtonian physics as the molecules would be striking the irregular carbon black surface from various angles and over short molecular time intervals. The individual molecules could not overcome the larger mass inertia of the radiometer vanes. Then the rarefied gas molecules acting in mass, via the  pressure differential  between the reflective and non reflective sides, could then over come the macro inertia of the vanes and harness.

G. The end result could be a force with no initial equal and opposite offsetting reaction and seemingly counter to Newtonian Physics. Yet this net force could have its base in Newton's physics - that a small force, as in a bouncing ball, would not over come the inertia of a  larger mass. In an analogy, a ball bouncing off a wall does not impart momentum to the wall. Only the direction of momentum is changed.  If the ball instead sticks to the wall the momentum of the ball is then expressed as heat transferred to individual molecular momentum. (I use this example as a misconception is that the bouncing ball would "somehow" transfer macro momentum to the wall when the wall itself would be immoveable.)

(Note: if other explanations would be forth coming I feel such explanations would need to account that little or no force would b exerted on the vanes in this initial energizing of the gas molecules.)

H. My understanding of radiant energy is little or no force would be exerted on the radiating mass. Hence in addition to the ball example, it could also be possible to create an imbalance when excess energy is re-radiated back out of the system (as the refrigeration effect above).

I. I confirmed applying carbon soot on aluminum works also works. It may be the carbon surface is able to provide the necessary insulation for the pressure differential.  I compared both stiff paper and aluminum. I first observed the same limited motion in both.  As the soot is easier to apply I am using aluminum as the base.  (Note as both carbon and aluminum are radiating surfaces I would anticipate the "refrigeration effect"  would not work with aluminum.)  However further testing could compare the net force being  generated  with insulating and non insulating surfaces of various thickness. 

I confirmed with a light weight carbon aluminum strip hanging with an off center hole on a carbon fiber rod that it was possible to move the strip down the rod.  The strip moved first with agitation a little down the rod then rapidly with a full circular motion around and down the rod. Extrapolating the weight from a larger aluminum strip the weight is about 0.002 grams. 


I am now almost certain that oscillations are necessary (from high to low pressure areas) to commence movement. This helps explain why I was not able to have heavier strips move along a rod - though a little back and forth movement took place. It helps explain why the control mounted radiometer vanes spin whereas the aluminum/carbon strips mounted on a rod showed little motion due to the friction and excessive weight preventing oscillations. 

Yet, if needing further confirmation of the necessity for oscillations, the small, light aluminum strip with its off center hole spun wildly around the rod as it moved down the rod.  The degree of energizing looked to me to match the radiometer vanes upon the application of a strong energy source.

In the radiometer the net force is directed into a centrifugal acceleration. Yet after observing the small spinning  aluminum strip rotating along its guide rod, the movement into a lower pressure area also could be "channeled" into a directional component which would not be fully rotational in nature. I feel the fact that the net force could be made to have a directional component has not been appreciated in the study of the radiometer net force.

Although the small strip was of small mass, a larger mass can be accelerated when the radiometer vanes and harness are well balanced.

What is also intriguing is the almost simultaneous deceleration of the gas molecules, now a dead weight, to give the net macro acceleration. This deceleration is being "masked" by the net acceleration of the vanes and harness. 

Newton's physics is focused on the taking apart and quantifying force. The radiometer force, in contrast, is a composite force. This is why, I feel, a more full explanation of the radiometer would yet be outstanding. A fuller explanation could require  looking at the radiometer as a total accelerative process, including the deceleration phase of the rarefied gas molecules.

For Further Consideration

1. The testing is to be under the supervision of those with experience in vacuum safety. 

2. At a low micron range where pressure differentials are not present, the actions of the individual atoms predominate. I would like testing  in say the 10 - 20 micron  range. 

3. A future test of these special properties could be as follows. Fix a set of elongated vanes inside an elongated light weight glass "bulb" using the high strength glass now available. The surface area could be say 5 times that of the typical hobby radiometer. Leave sufficient space around the vanes for the rarefied gas reactions. A small opening is left in the "bulb" to equalize the rarefied gas pressure with the vacuum chamber. Instead of the vanes pivoting on an interior needle, glue a thread on top of the "bulb" to suspend the "bulb" from the top of the vacuum chamber. The object of this test would be to show that it could be possible for the net force to be directed outward to the external rotation of the "bulb". 

I feel the radiometer force is a composite force which includes deceleration. The radiometer force also takes place over a sequence in time which is not included in Newtonian physics. Yet, I feel the radiometer mechanics also requires a focus on Newtonian physics.

It is intriguing to me, with the input of energy, the rarefied gas molecules are trapped to be reused with no external exhaust released.

Ref. MIT news 10/4/2013

In regards to this reference it is now demonstrable what I was attempting to demonstrate with the radiometer - that a force can be created from within a mass to cause the acceleration of the total mass. This article is focused on robotic applications. Yet that a mass can be internally accelerated is possible.

The M-Block robotic demonstration is with an internally generated force many times greater then in a radiometer.

The M-Block demonstration has as its "base" for the acceleration a connectedness to an earth surface. Yet , as a speculation, it might be possible to use the inertia of the body itself as a "base" for an internally accelerative force - without connectedness to an external surface.  Updated October 18, 2013  and 2/12/2014 (minor editing).