From: heathjohn2@gmail.com   
      
   On Wednesday, March 7, 2018 at 1:35:44 PM UTC-5, Edward Prochak wrote:   
   > 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   
      
   You are over thinking. There is a short cut. You did not stretch the   
   elastic band. Only the tendency of arms to spread out while spinning   
   stretch the elastic band. Only energy from angular momentum stretched   
   the elastic band not human power. With this in mind your short cut is   
   energy was gained to stretch an elastic band. It did not come from the   
   human energy so it had to come from angular momentum. As the the human   
   was on a turn table when these actions took place the angular momentum   
   of the box could not be effected. Therein is the rub. The equal angular   
   momentum of the box and human on the turn table are no longer   
   equal. Angular moment as not been conserved. The one on the turn table   
   gave part of his angular momentum to stretch an elastic band. In effect   
   nature was taken momentum in exchange for energy , stretched elastic   
   band. As long as the elastic band remains stretched ENERGY conservation   
   laws prevent restoration of angular momentum conservation between the   
   box and the human on the turn table.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)