Dewing.PA@XEROX.ARPA (09/21/84)
In Larry Nivens book 'The Integral Tree' I don't understand the 'gravity'. In
the tree tufts there is 'gravity' and in the mid-trunk area there is zero g. How is
this possible. The tree doesn't rotate end for end, one end is always toward Voy.
Can anyone out there explain it in a relatively simple manner?
Thanks Ahead,
John Dewing
P.S. I thought it odd that in the seamingly male oriented society on London Tree
that the Scientists Aprentice was female.katz%uci-750a@sri-unix.UUCP (09/25/84)
From: Martin D. Katz <katz@uci-750a>
In Larry Nivens book 'The Integral Tree' I don't understand the
'gravity'. In the tree tufts there is 'gravity' and in the mid-trunk
area there is zero g. How is this possible.
The 'gravity' you speak of is not gravitational attraction from the tree,
but rather a tidal effect caused by gravitational attraction from Voy (the
star the trees orbit). The tree is in an orbit which is approximately that
of its center of mass. The end of the tree closest to Voy is under a higher
gravitational pull, but the tree doesn't move toward Voy because the
opposite end has a balancing decrease in gravitational pull.
The people on the close end feel this higher pull relative to the average
pull on the tree, and thus have a net gravitational acceleration (which they
feel as weight) relative to the tree. If they let go, they fall toward Voy
(thus, Voy is under their feet). On the far end, the attraction of the
people is less than the average for the tree, so people tend to fall out
away from the tree, and Voy is in the sky for them.
The effect is also what keeps the ends of the tree pointing directly toward
(away from) Voy. The same effects are at work between the Earth and Moon.
The Moon always keeps the same face toward the Earth because of tidal
effects. In addition, the tendency of tidal effects to push objects away
from the center of gravity of the moving object (e.g. the Earth) is what
causes high tides when the Moon is above and directly below (mere direct
gravitational attraction on the water would cause high tides to be only
every 24 hours, not every 12 hours).
Hope this long winded note explained more than it bored.