Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site utcs.uucp Path: utzoo!utcs!webber From: webber@utcs.uucp (R. D. Webber) Newsgroups: net.physics Subject: Re: cancelling forces Message-ID: <877@utcs.uucp> Date: Mon, 23-Sep-85 20:19:20 EDT Article-I.D.: utcs.877 Posted: Mon Sep 23 20:19:20 1985 Date-Received: Tue, 24-Sep-85 02:50:21 EDT References: <546@sri-arpa.ARPA> Reply-To: webber@utcs.usenet (R. D. Webber) Organization: University of Toronto - General Purpose UNIX Lines: 33 Summary: Small differences are important In article <546@sri-arpa.ARPA> sloan@uw-tanga.arpa writes: >From: Kenneth Sloan> > >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). > >Here's the question... If I place [two robots] 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 Well, for one thing, unless you're assuming no slip at the robots' 'feet' and 'hands', there's some friction. There's also likely to be energy loss due to slip and chatter in internal actuators. You may, however, wish to consider these negligible. In that case, my thought is that, since work is force through displacement, there is no work done and therefore no energy loss apart from 'life' support. Oh, yeah, also some work done in deforming the structures of the box, the robots, and whatever the robots react against, but that's negligible unless you've got some REAL MOTHERF***ING big robots with a lot of power. Bob