<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD> <META http-equiv=Content-Type content="text/html; = charset=iso-8859-1"> <META content="MSHTML 6.00.2800.1106" name=GENERATOR> <STYLE></STYLE> </HEAD> <BODY> <DIV><FONT color=#800080>Professor Fowler's comments make complete = sense to me. But I do not understand some things that your folks state.</FONT></DIV> <DIV> </DIV> <DIV>"If you then push down on one end and let go the see saw will rock = back and forth until slowly it refinds its state of equilibruim."</DIV> <DIV> </DIV> <DIV><FONT color=#800080>Why would it rock back and forth? I don't = think it would. If you push down on one end, it will continue with the rotational = movement you imparted until either friction stopped it, or until one end = hit the ground perhaps. If, as the professor says, the seesaw has the axle right = through the center of gravity of the plank, it would always be in equilibrium, = and have no need to "seek" some state of equilibrium.<BR></FONT></DIV> <DIV>"I understand that friction is the thing that brings it back into equilibruim, ..."</DIV> <DIV> </DIV> <DIV><FONT color=#800080>It will always be in equilibrium, friction = will only serve to slow the rotational movement.</FONT></DIV> <DIV><FONT color=#800080></FONT> </DIV> <DIV>"...but why the rotational movement to begin with exactly?"</DIV> <DIV> </DIV> <DIV><FONT color=#800080>Because a seesaw is constrained in that = manner, only allowing rotational movement. Or am I missing something = here?<BR></FONT></DIV> <DIV>"Science answer: Gravity applied to the see saw,  gravity = applied to the weight, force/counter force etc."</DIV> <DIV> </DIV> <DIV><FONT color=#800080>I don't think gravity really has much net = effect in this situation - other than to keep things from flying away from us.</FONT></DIV> <DIV> </DIV> <DIV>"Ya think ?? Funny how a phsyics professor seemed to miss = this..."</DIV> <DIV> </DIV> <DIV><FONT color=#800080>Don't understand your thinking here at all.</FONT></DIV> <DIV> </DIV> <DIV><FONT color=#800080>Terry Farrell<BR></FONT></DIV> <DIV> </DIV> <DIV>Brian Lawson wrote:</DIV> <DIV> </DIV> <DIV>> Science answer: Gravity applied to the see saw,  gravity = applied to the<BR>> weight, force/counter force etc.</DIV> <DIV> </DIV> <DIV>Ya think ?? Funny how a phsyics professor seemed to miss this... or = did he.<BR>Perhaps you could take a shot at being a bit more specific..... = ??</DIV> <DIV> </DIV> <DIV> <SPAN id=__#Ath#SignaturePos__></SPAN> </DIV> <DIV>----- Original Message ----- <DIV>From: "Richard Brekne" <<A href="mailto:Richard.Brekne@grieg.uib.no">Richard.Brekne@grieg.uib.no</= A>></DIV> <DIV>To: "PTG" <<A href="mailto:pianotech@ptg.org">pianotech@ptg.org</A>></DIV> <DIV>Sent: Friday, February 28, 2003 2:44 PM</DIV> <DIV>Subject: A "simple" see saw question</DIV></DIV> <DIV><BR></DIV>> List...<BR>> <BR>> In my pursuit of a better understanding of the concept of Balance Weight and in<BR>> general = of  grand action leverage ran into this seemingly simple question, = and<BR>> posed it to several folks around the world. Here is a response I found<BR>> = particularilly interesting.<BR>> <BR>> From<BR>> <BR>> = Michael Fowler wrote<BR>> Commonwealth Professor<BR>> Department of Physics<BR>> University of Virginia<BR>> <BR>> > Richard = Brekne asks:<BR>> <BR>> > >Given a see saw with say 10 kilos weight = 1 meter on each side of the<BR>> > >fulcrum. If you then push down on = one end and let go the see saw will<BR>> > >rock back and forth until = slowly it refinds its state of equilibruim.<BR>> > >Why exactly  = does this happen ?  I understand that friction is the thing<BR>> > = >that brings it back into equilibruim, but why the rotational movement = to<BR>> > >begin with exactly ?<BR>> ><BR>> > >Richard = Brekne<BR>> ><BR>> > Perhaps you think I know something about seesaws = because of my notes at<BR>> > <A href="http://www.phys.virginia.edu/classes/581/RotationalMotion.html">h= ttp://www.phys.virginia.edu/classes/581/RotationalMotion.html</A><BR>>= ><BR>> > I agree with you that IF a seesaw has the axle right = through the center of<BR>> > gravity of the plank, there's no reason why = it should go back to a<BR>> > horizontal position.  But I've seen = seesaws in playgrounds where it<BR>> > definitely does go back to horizontal = -- I believe these must be built with<BR>> > the center of gravity of = the plank slightly BELOW the axle, so the stable<BR>> > position is horizontal.  I also seem to remember some very fancy = seesaws<BR>> > with hydraulic dampers -- obviously, these could be adjusted to keep = the<BR>> > rest position horizontal.<BR>> <BR>> So... either he = misunderstood the question... or I've some more head scratching<BR>> to do. = :)  whatelse is new eh ?<BR>> <BR>> <BR>> --<BR>> Richard = Brekne<BR>> RPT, N.P.T.F.<BR>> UiB, Bergen, Norway<BR>> <A href="mailto:rbrekne@broadpark.no">mailto:rbrekne@broadpark.no</A><BR>&= gt; <A href="http://home.broadpark.no/~rbrekne/ricmain.html">http://home.broad= park.no/~rbrekne/ricmain.html</A><BR>> <BR>> <BR>> = _______________________________________________<BR>> pianotech list info: <A href="https://www.moypiano.com/resources/#archives">http://www.ptg.org= /mailman/listinfo/pianotech</A></BODY></HTML>