Richard S. Norman
rnorman at umich.edu
Mon Dec 9 20:26:47 EST 2002
On Mon, 09 Dec 2002 20:01:57 -0500, Jerry Avins <jya at ieee.org> wrote:
>Gary Bergstrom wrote:
>> > > jmdrake wrote:
>> > http://www.americanantigravity.com/
>> > While on the surface it may seem "cranky" the fact is that their
>> > flyer actually works. Now if it works by true "antigravity" or
>> > by some other force is a big question. But the plans are pretty
>> > simple and the results have been reproduced many times over.
>> > However someone might mislabel them "cranks" just because they
>> > have the word "antigravity" in their URL.
>> > Regards,
>> > John M. Drake
>> The first time I saw this was on the cover of a Popular Science (I
>> think) in the '60s. Not antigravity, just propulsion by moving air.
>> The models are so light, because it's hard to move much air without
>> arcing. (That old model on the cover was square rather than
>> triangular, but otherwise looked the same!)
>> And yes, I would label (NOT mislabel) them cranks because of the word
>Waddya mean, "cranks"? Antigravity devices are all around us. I'm typing
>right now on a keyboard a little higher than my lap. You can bet that
>gravity would pull it down pretty quick it there weren't something
>preventing that. The same goes for what's holding me up. Those things
>must expend energy continuously to do what they do. If you think that
>there can be no work without motion, just hold a full gallon jug still
>with an extended arm and tell me that it's only hard to do if it moves.
Yes, I will tell you: there is no work without motion (or the
equivalent for non-mechanical forms of work). Your muscles can get
very tired without doing external work. You can push against a stone
wall all day, even a metaphorical stone wall, and exhaust yourself
without doing one erg of external work.
"Hard to do" does not require work in the technical physics sense!
Technical terms have technical meanings, whether you like them or not.
Antigravity has a specific meaning. It means it eliminates or reduces
gravity, not simply supports an object or elevates it against an
unchanged gravitational force. And anyone who claims to work with
antigravity is deserving the label "crank".
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