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From: sloan@uw-tanga.arpa
Newsgroups: net.physics
Subject: cancelling forces
Message-ID: <546@sri-arpa.ARPA>
Date: Mon, 16-Sep-85 15:50:00 EDT
Article-I.D.: sri-arpa.546
Posted: Mon Sep 16 15:50:00 1985
Date-Received: Thu, 19-Sep-85 07:27:55 EDT
Lines: 24

From:  Kenneth Sloan 


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
energy into it, and get most of that energy out as work performed on
the box (the rest being lost to maintain the robot's life support systems).

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.
Now the output of this system is a moving box with the same direction
and twice the speed.  I'm putting twice as much energy in and getting
twice as much energy out.

Here's the question...  If I place them on opposite sides of the box,
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
somewhere?

-Ken Sloan