Propulsive Effects of a Rotating Mass 



Tests on Dry Ice Moving on a ■■■■■' * ■' 

 Horizontal Smooth Slate 



As it is known according to the principles 

 of mechanics, a body not subjected to any force 

 either remains at rest or moves at a uniform 

 speed. In practice, it happens that a body put 

 into motion by an initial thrust, slows its own 

 motion gradually because of friction, and stops. 

 However, if the friction is very small, the 

 body is able to maintain a constant speed for 

 quite a long time. 



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Fig. 23 - Diagram of a 

 test with the device sus- 

 pended from a thread 



In order to create in the laboratory a motion with very low friction, we re- 

 sorted to small pieces of smooth dry ice on a horizontal slate that was likewise 

 accurately smoothed. The friction derived from it is, in effect, very low. In 

 fact, a piece of dry ice pushed by a light puff of air, can run the length of the 

 slate at a uniform speed. Glass is less suitable than slate, because the ice, 

 which melts little -by -little, sticks to the glass very easily. 



The friction coefficient for dry ice in motion on a smoothed slate, accord- 

 ing to experiments specifically carried out by us, is equal to about 0.001. As 

 may be recalled, the coefficient of friction for steel on ice, as given by the 

 manuals, is 0.01. 



A device with two masses, with an overall weight of 140 grams, was posed, 

 by means of a light wooden frame, on four small pieces of dry ice placed on an 

 accurately smooth slate 3.20 meters long and 0.50 meters wide. Numerous 

 tests of systematic type were carried out, with the device running over the 

 slate in all directions. The tests were repeated with another device weighing 

 120 grams. The final result of these tests was that the device-frame-ice com- 

 plex, according to the way in which the device is oriented on the slate, (a) ad- 

 vances on the slate with rectilinear and uniform motion, (b) turns to the right, 

 (c) turns to the left, and (d) launched at low speed from extremity A to the other 

 extremity b of the slate, at a certain point stops and returns backwards. As is 

 apparent, a friction resistance that is of the order of thousandths of grams 

 does not impede the functioning of the apparatus. 



It should be noted that in the last case, both the dynamic action of the ro- 

 tating masses that brings the frame back again and the friction resistance are 

 headed in the same direction: from B toward A. 



Graph of the Forward Motion of the Device 



A large sheet of paper was laid out on the floor, and on it the device (Fig. 9) 

 was made to advance, carrying a penpoint for writing on the paper. The pen- 

 point was more or less in correspondence to the vertical passing through the 



1389 



