Re: [Phys-l] Trampoline G Forces

["John M Clement" <clement@hal-pc.org>]

The most objectionable part of the ad is the claim that gravity pulls 
you down at the bottom of the cycle.  The use of G force is common 
usage, namely that the G force is the apparent gravitational force 
which would be -normal force.  The implication that the gravitational 
force is only present at the bottom lines up with common 
misconceptions.  As to weight, I agree that it depends on the 
definition.  Some authors define weight as the quantity measured by a 
spring scale, so it goes up and down when you accelerate in an 
elevator.  The problem with G force is that it is not a physical force 
in an inertial system, so it is confusing to students, and should 
never be used in science classes.

John M. Clement
Houston, TX

> Bones are piezoelectric and need stress in order to maintain 
> strength.
> The lymphatic system has no central 'heart' to keep it flowing - so 
>
> it depends upon body motion for it's 'driving force'.
>
> Space Station residents and their medical handlers are constantly  
> looking for effective ways to provide repetitive accelerations of  
> various body parts. (Isometrics don't seem to be very effective.)
>
> If the complaint centers on the use of the term G-forces - then  
> please note that the article is aimed at the 'General Public' rather 
>
> than Intro Physics gurus.
>
> 'We' complained loud enough and long enough for nasa to stop  
> referring to the 'weightlessness' of orbiting stuff - that we are 
> now  
> stuck with 'micro-gravity' instead.
>
> I much preferred 'weightlessness' as opposed to 'greatly reduced  
> gravitational field'.
>
> (weight = one's contact force with the environment)
>
>
>
> > > "NASA scientists agree with what we have learned  . . . They
> > > discovered that since the cells of the body live in an essentially
> > > zero-gravity environment, it's beneficial to alter the G-force in
> > > order to stimulate the body's lymphatic system which removes toxins
> > > from the cells.  Rebounding, they discovered, is the only excercise
> > > proven to exert the maximum amount of "pull" on the human body  
> > > down to
> > > the cellular level, with the least amount of effort.
> > >
> > > . . . .
> > >
> > > Gravity pulls you downward during the low point of the rebound cycle
> > > just as our super-flexible pad pushes you upward into 
> > > weightlessness.
> > > During the rebound, you experience 2 to 4 "G-forces" meaning that
> > > gravity works for you instead of against you.  During this short
> > > interval of added G-forces, your body acts as if it's carrying a  
> > > heavy
> > > weight.  This period does not last long enough to produce strain, 
> > > but
> > > it's just long enough to start  . . . Cleansing your arteries  . . .
> > > Cleansing your lymphatic system . . . Cleansing every cell in your
> > > body . . . tone every muscle . . . strengthen your muscular-skeletal
> > > mass . . ."