3 ms·
Great :-) <pet_peeve> Can we say "free-fall" though? The ISS has at least 90% of the gravity we have down here... not very micro! </pet_peeve>
by vmilner 14y ago
Great :-)
<pet_peeve>
Can we say "free-fall" though? The ISS has at least 90%
of the gravity we have down here... not very micro!
</pet_peeve>
- ColinWright 14y agoWell, yes and no. When you are in free-fall, and everything around you is in free-fall, then in that frame of reference there is (to first order) no gravity. The slight variations caused by different altitudes and so forth lead to tidal effects, which are really small, and hence we (using the editorial "we") refer to them as "micro-gravity". Of course, in truth there is nowhere in the universe that has absolutely zero gravity, so the terms "X-gravity" for X chosen from { "zero", "micro" } become useless unless we agree to use them somewhere, and the free-fall environment seems pretty much as good a place as any to use these terms. But this actually amounts to an admission that you are right, but that I'll probably still use the term "micro-gravity".
- vmilner 14y agoFair enough. I guess I always think of "gravity" as "gravitational field strength caused by matter" (the gradient of "Einstein's rubber sheet", if you like), so a free-falling object near Earth will always have plenty.
- ColinWright 14y agoI think of it like that, but then relativize it to the motion of the reference frame. To see how, take the usual visualization of the gravity well and mark on it where you are. Then take a tangent plane at that point. The gravity well is below that plane, and hence falls away from you, along the line towards and away from the gravity source, but is above the plane in the fore/aft direction. This explains why tidal forces act inwards in a plane perpendicular to a line joining you with the gravity source, but outwards along that line. It's a useful visualization.