Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site petsd.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxj!houxm!vax135!petsd!cjh From: cjh@petsd.UUCP (Chris Henrich) Newsgroups: net.sf-lovers Subject: Re: Gravity on an Integral Tree Message-ID: <355@petsd.UUCP> Date: Mon, 24-Sep-84 18:58:43 EDT Article-I.D.: petsd.355 Posted: Mon Sep 24 18:58:43 1984 Date-Received: Wed, 26-Sep-84 07:23:39 EDT Organization: Perkin-Elmer DSG, Tinton Falls, N.J. Lines: 35 [This space intentionally left blank] > 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? In a word, "tide". An integral tree, or any other reasonably small object in orbit, moves as if its mass were concentrated at the "center of mass." (Halfway up the trunk.) If it is in a circular orbit, then the gravitational force at that distance from Voy is equal to the centripetal force needed to keep the object in that circular path. At the inner tuft, which is closer to Voy, the gravitational attraction of the star is greater, and the centripetal acceleration needed to keep in that orbit is less. So a person in the tuft feels a pull towards Voy. Likewise, in the outer tuft, the gravitational attraction is less, and the centripetal acceleration needed to keep up with the integral tree is greater, so a person there feels a pull outwards. The integral tree itself is under tremendous tension, which explains why it can come apart if it is weakened at the middle. This force is called "tidal stress" because the same mechanism explains the tides of Earth's oceans: the major gravitational attractor being the Moon. Regards, Chris -- Full-Name: Christopher J. Henrich UUCP: ..!{decvax,ucbvax,ihnp4}!vax135!petsd!cjh US Mail: MS 313; Perkin-Elmer; 106 Apple St; Tinton Falls, NJ 07724 Phone: (201) 870-5853