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From: kim@mips.UUCP (Kim DeVaughn)
Newsgroups: net.physics
Subject: Re: cancelling forces
Message-ID: <195@mips.UUCP>
Date: Sun, 22-Sep-85 23:49:41 EDT
Article-I.D.: mips.195
Posted: Sun Sep 22 23:49:41 1985
Date-Received: Wed, 25-Sep-85 11:43:37 EDT
References: <546@sri-arpa.ARPA>
Organization: mips ... where RISC is a way of life
Lines: 34

[ ... go ahead, eat my bits ... ]

> From:  Kenneth Sloan <sloan@uw-tanga.arpa>
> Here's a new subject to think about, start aguments, etc.
> 
> Let's say I have a robot that pushes a box.  I put a certain amount of
>
> Now I set up another one of these, and place it alongside the first
> robot.  I have them push in the same direction so that the forces add.
> 
> the pushes will cancel.  Now I appear to be getting no energy out of
> this system, at least not in the form of a moving box.  I am still
> putting as much energy into the system.  All I did was move one of the
> devices.  What is happening to the energy?  Is there an output in
> another form of energy?  Is it building up in one of the devices

Heat.  If your robot's motors have sufficient torque, their treads (or
wheels, or whatever) will "slip" against the surface they're "pushing
against" (i.e., friction).  Less torque, and the motors will heat up due
to "electrical friction" (i.e., hysteresis, I-square*R losses, etc.)
The surface is part of the system (and if it were "removed," you'd have
your robots in space, and there would be no motion irrespective of which
side the 'bots were on).

/kim

> -Ken Sloan

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