Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site shell.UUCP Path: utzoo!watmath!clyde!burl!ulysses!gamma!epsilon!zeta!sabre!bellcore!decvax!genrad!grkermi!panda!talcott!harvard!seismo!ut-sally!utmbvax!shell!buck From: buck@shell.UUCP Newsgroups: net.bio Subject: Re: Up The Down Escalator Message-ID: <119@shell.UUCP> Date: Tue, 11-Jun-85 10:22:11 EDT Article-I.D.: shell.119 Posted: Tue Jun 11 10:22:11 1985 Date-Received: Thu, 13-Jun-85 23:57:21 EDT References: <237@ihnet.UUCP> Distribution: net Organization: CS Dept., Shell Development Co., Houston Lines: 29 I have never read so many consistently incorrect replys on this network! If all you armchair physicists would go out and actually test out your theories, you would *very* quickly discover that it takes much, much more effort to go up the down escalator than to go up stairs. I say this as someone who has run up down escalators on numerous occasions, and as a professional physicist. Now, why is the escalator so much more work? Power expended is ForceVelocity. Integrate to get kinetic energy , .5mv**2 . So, for example, in accelerating something from rest to v=2, only one quarter of the energy is expending from v=0 to v=1, and three quarters is spent from v=1 to v=2. Well, then it ought to get easier to accelerate things as they speed up because the velocity is going up in ForceVelocity, right? Wrong - it just practically becomes *much* more difficult to keep the same force on something that is moving away from you. Exactly the same thing is occuring with the foot trying to apply a force to the escalator. Just do a simple thought experiment - speed up the escalator enough and the man can make no net progress, he just can't move his leg (impulsively) down fast enough to get any reaction force from the escalator, so he can't make any net progress. It is left as an excercise for the student to fill in the gaps in the above and make a rigorous proof, or just step over to your nearest stair/escalator combination... A. Lester Buck @ Shell Development Co. {ihnp4, pur-ee, ut-sally}!shell!buck