well, G force is a measure of relative measure of an apparent force, but since your mass doesn't change (usually) it really is directly related to the experienced acceleratoin.<br /><br />For instance, if I was in free fall near the moons surface (with 1/6 the gravity) I would not say I was experiencing 1/6th G forces, even though I am at 1/6th the acceleration. I wouldn't be wrong, but I'd be using the term a little oddly. Since I experience no apparent force (I'm in free fall, so I'm mimicking zero gravity) I'd more likely say I was experiencing 0 G.<br /><br />But, it's a quick and easy way of giving a force meaning, as every whole unit of "G force" is multiple of my own weight when standing still on earth. So 2 g's, everything about me is 2x heavier, from effort I have to do to lift my arms, to the work my body has to do moving blood, breathing, and the weight of my organs. 4 "G's" is 4x my weight, 4x the effort, etc. <br /><br />Astronauts experience 4 G's during launch IIRC, fighter pilots can, with training and pressure suits (that help keep blood in the right spot by applying pressure) withstand up to 8 or so G's during tight, high speed turns before blacking out.<br /><br />Ocassionally you'll run into a term of "negative" G's...it's the same thing, but the force isn't directed towards your feet, but towards your head. This happens when you're on the "outside" of a turn. Imagine a roller coaster loop-the-loop, with your head pointed towards the inside of the loop (to the center). This will give you "positive" G's as the apparent force of the coaster will be towards your feet. If you were on a fancier more modern coaster, you will occassionally be on the "otuside" of the loop, with your feet pointed to the center. This has the apparent force (still away from the center) going towards your head.<br /><br />The physiological difference is positive G's give you black outs (blood drains from your head, towards your feet) and your vision greys and blacks out. <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>