Re: how do you know when you experience negitive g's

Under normal conditions, we experience the force of one gravity (1g).  This 
is the force that creates weight.  The downward pull of gravity has been 
deemed to be positive g's.

Zero-o gravity, which is also known as Microgravity or weightlessness, can 
be created by placing an object into free-fall.  Gravity is still acting 
upon the object, but since the object is falling, it is in a different 
inertial reference frame.

Weightless conditions are experienced by astronauts in the Space Shuttle.  
This condition can also be created on Earth by being in free-fall.  Many 
amusment park rides place the riders in free fall for 1 or2 seconds.

Another way to experience weightless is in an airplane that is flying a 
parablic flight trajectory.  This is how the NASA reduced-gravity aircraft 
laboratory (a.k.a. the Vomit Comet) creates 20 seconds periods of 
weightlessness.

Negative g's is a condition that can occur while flying in an airplane.  
During negative g's, objects (and people) are 'pulled' upwards.  

For more information on microgravity:

http://zeta.lerc.nasa.gov/new/school.htm#explain