From: edprochak@gmail.com   
      
   On Tuesday, February 27, 2018 at 4:02:12 AM UTC-5, John Heath wrote:   
   []   
   >   
   > Fair enough. I will do my best to put you in check mate with regards to   
   > angular momentum by bribing nature with a little energy under the table.   
   >   
   > You are in a box in space and both yourself and the box are not rotating   
   > relative to the stars that can be seem out the window. You now step on a   
   > turn table spin yourself clock wise CW. This causes the box to turn   
   > counter clock wise , CCW . You are turning CW and the box CCW. Angular   
   > momentum has been conserved. I will ask you to put an elastic band   
   > between your thumbs then allow your hands to spread out caused by your   
   > CW spin. Lock the elastic band in the stretched position. Check mate as   
   > you just bribed nature with the currency of energy , stretched elastic   
   > band. As you were on a turn table when you did this the spinning of the   
   > box was not effected. As long as you have a locked stretched elastic   
   > band in your hand the total angular momentum of yourself and the box can   
   > not be restored to zero without violating energy conservation laws.   
   >   
   > I have an open mind to a counter argument.   
      
   The solution is simple as long as the rules are applied correctly.   
   Words fail to reach the correct answer in your example.   
      
   At start net angular momentum is zero L = I * w = 0   
   (Using w for omega, the angular speed)   
      
   For you to turn, the box also turns such that L = 0   
      
   so Ib * -wb + Ip * wp = 0  ==> Ip * wp = Ib * wb   
      
   with b for the enclosing Box and p for the person on the turntable.   
   Also, where the negative indicates the CCW rotation direction.   
   Important to note the rotational speed is unlikely to be the same   
     wp =/= wb   
      
   So looking at just the person the angular momentum is initially   
     Lp = Ip * wp   
      
   Now holding the elastic band, you stretch your arms.   
   The momentum is conserved Lp = Ip' * wp'   
   but the rotational speed changed because of the change in the   
   moment of inertia (Ip).   
      
   Now you lock the elastic band. You return your arms to their original   
   position, so we get to Lp = Ip" * wp"   
   Note this is double prime values, BECAUSE while the elastic band has   
   very little mass, it does contribute to the moment of inertia I.   
   So the final moment of inertia Ip" =/= Ip' and the rotational   
   speed is proportionally different also.   
      
   So you conclusion is wrong. The momentum of the box + person   
   started at zero and remained at zero the entire process.   
      
   With modern high speed video you can easily test this.   
   I would suggest instead of an elastic band, you use something   
   heavier, like a metal spring. You will see the final speed   
   is not the same as the starting speed.   
      
   Final note. yes my analysis assumed momentum is conserved, but   
   that is the purpose of real experiment versus the thought experiment   
   above.   
      
   HTH,   
   ed   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)