Challenger Logo by Alan White   A Science Fiction Fanzine   Autumn/Winter 2003-2004

A discussion has been raging in the Southern Fandom Press Alliance about Cavorite, the anti-gravity substance created by H.G. Wells for his marvelous novel, The First Men in the Moon. Ned, a retired NASA wind-tunnel engineer, has chimed in as follows …

 

 

WEIGHTY COMMENTS ON
Cavorite

Cuyler W. "Ned" Brooks

Cavorite - a substance that could block the gravitational field (as metal, or any conductor, can block the electrostatic field).

         All objects create a gravitational field in proportion to their mass - it is the interaction of these fields that we perceive as gravitational attraction. If Cavorite were interposed between the Earth and a bowling ball, the bowling ball would no longer be attracted to the Earth. The Earth would no longer be attracted to the bowling ball either, but that would not be noticeable!

         What would happen to the bowling ball? Well, it would be faintly attracted to distant masses on the other side of the Cavorite from the Earth, but probably not enough to measure. The big effect would be the ball's own velocity - if it were at the Earth's equator, it would be going about 1000 m.p.h. on a curved path, and the centripetal force would act in the upward direction, causing the ball to rise.

         The ball would rise with an acceleration of

 

         Not exactly zooming, and of course if the ball drifted out of the area where the gravity was blocked it would immediately fall back with an acceleration of 32. Furthermore, it could be held in place by a piece of dental floss - if the ball weighs 5 lbs -= 80 oz, the force required to restrain it would be proportional to the acceleration, as the mass is constant. The force exerted on the ball by an acceleration of a = 0.1would only be about 0.25 oz.

         On the other hand, if the experiment were carried out at the North Pole, the bowling ball would merely become weightless, acted on by very small unaligned forces. After a while it would drift back into the Earth's gravitational field and fall to the ground (or the ice or the deck or whatever there might be to stand on at the North Pole).

         It has been objected that the very existence of Cavorite would violate Newton's laws, because at the edge of the "shadow" blocking the gravitational field a perpetual motion machine would become possible. That is, if a wheel were mounted vertically with the axis on the border and half the disk in the Earth's gravitational field and the other half above the Cavorite, the wheel would spin without energy input because half of it was pulled earthward while the other half was not. In fact, if energy were not removed from the wheel (as by a brake or an electric dynamo), the wheel would spin faster and faster until it either reached an equilibrium with air and bearing friction or exploded when the centripetal strain exceeded the strength of the material.

         This is an important objection, but I'm not sure what connection it has to do with the problem. There are, after all, other ways to cancel gravitational attraction on half of a vertically mounted wheel! Suppose we use our 5-lb bowling ball (since we have already done the math on that) as a wheel by sticking an axle through it - now half the ball will be accelerated toward the Earth (a = 0.1 feet/sec) , while the other half will not. How could this be accomplished without Cavorite? Well, half of the ball could be in a tank of liquid with the same density as the ball itself. There is nothing technically difficult about that! Any conceivable seal at the vertical interface between the dry side of the ball and the wet side of the ball would exert more force opposing the rotation of the all that could be overcome by the approximately 5-inch-lb torque available from the asymmetric force on the ball - but that is a mere technicality.

         Suppose the ball were suspended between two tanks, one containing the liquid whose density matches that of the ball (thus making half the ball weightless) and the other some much lighter fluid that is immiscible with the heavier liquid (like oil and water). Now only a light seal would be needed at the interface, because the small amount of the lighter fluid that got through into the heavier fluid would float to the top of the tank where, if the tanks were both exactly full, it would flow back into its own tank. Whatever heavy fluid got into the light-fluid tank would fall to the bottom, where it could be returned to its own tank by a small scavenger pump.

         So we don't need Cavorite to extract energy from the gravitational field with an asymmetrically loaded rotating wheel.


         And on another matter ...

         But wouldn't a single atom of Cavorite have little effect? It seems to me that it would block the gravitational field of the Earth (the only one around that can be measured easily) only in a tiny cone above that atom. Beyond that any mass acted on by the Earth's field would still feel the pull of most of the Earth's mass - think of the shadow of a flea sitting on a light bulb. To another flea just off the surface above him there would be some shade, but a couple of flea-lengths out the other flea would be pretty much illuminated.


         And yet again ...

         So how large a Cavorite shield would we need to get to low Earth orbit, say 150 miles up, where the main engines could be used to achieve orbital velocity without working against atmospheric drag? Alas, it's a good thing the Cavorite shield can be only one atom thick, because to achieve full nullification of gravity to 150 miles, it will have to be about 2000 miles in diameter. Well, most of the atmosphere is in the first 50 miles above the surface - how big a shield would that take? Still over 1000 miles across.

         This of course is based on the assumption that the Cavorite itself has weight! If it can (unimaginably) shield itself against the gravitational pull of the Earth, then we need only coat the ship itself with it and be off to conquer the universe! 

 

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