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From: jpexg@mit-hermes.ARPA (John Purbrick)
Newsgroups: net.bio
Subject: Re: Up The Down Escalator
Message-ID: <2411@mit-hermes.ARPA>
Date: Thu, 6-Jun-85 12:55:48 EDT
Article-I.D.: mit-herm.2411
Posted: Thu Jun  6 12:55:48 1985
Date-Received: Wed, 12-Jun-85 00:12:19 EDT
References: <237@ihnet.UUCP>
Distribution: net
Organization: The MIT AI Lab, Cambridge, MA
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> Is it harder work climbing stairs or going up a down escalator?
> Karl Dahlke    ihnp4!ihnet!eklhad

This belongs in net.puzzles.
Imagine a sealed box put over the person on the escalator. It would be
impossible to tell if one was climbing or not, only that the stairs were always
moving under one's feet. Hence, it's intuitive that the amount of work done is
the same. But where does the energy go? It goes to backdrive the escalator's
motor--in other words, it will draw less power (or even, if it's designed by
a physicist, return power!) from the electric supply.

Or imagine the escalator replaced by a smooth, moving belt. To stop oneself
slipping down, one would have to exert a force up the belt, and one would
have to expend that force through a distance in order to hold one's position.
Mechanical work can be represented as (force * distance_through_which_force_is_
moved). QED.

John Purbrick					jpexg@mit-hermes.ARPA
{...decvax!genrad!  ...allegra!mit-vax!}  mit-eddie!mit-hermes!jpexg