From: banerjeeadda1234@gmail.com   
      
   On Sunday, February 18, 2018 at 10:40:59 AM UTC+11, John Heath wrote:   
   > I am going to fire a cannon ball west. In doing so the cannon ball   
   > will move fast west and the cannon slowly east. Was momentum   
   > conserved? Yes as the mass of the cannon ball is small compared to   
   > the cannon plus the earth it is anchored to. The earth is now turning   
   > slightly slow and the cannon ball fast so momentum is conserved.   
      
   The Earth's will regain speed to its former level when the cannon ball   
   loses its momentum to the Earth.   
   >   
   > So it would seem however there are energy conservation laws as well   
   > that can not be violated. There can not be a violation to momentum   
   > or energy conservation laws.   
      
   Energy conservation laws are very dicey. Very tricky. Consider   
   permanent magnets for instance - pm motors have been around now for   
   ages with pms replacing electromagnets. Then there is the Perendev   
   simulation realised by Pakistani scientists, where pm motors generate   
   energy out of no known input energy source.   
      
   Again, when you consider the law of conservation of angular momentum   
   for say a dancer rotating fast with arms pulled in, and slower with   
   arms pulled out, then with the variation of I you will get different   
   values of rotational kinetic energy.   
      
   [[Mod. note --   
      
   1. Permanent magnets don't violate conservation of energy.   
      
   2. The "Perendev motor" is Yet Another Claimed Perpetual-Motion Machine   
      that somehow never works when independent observers are around, so   
      Ockham's razor strongly suggests that it's a fraud.  For anyone who   
      hasn't seen it, Arthur W. J. G. Ord-Hume's book "Perpetual Motion:   
      The History of an Obsession" is a fascinating history of the subject.   
      
   3. The "different values of rotational kinetic energy" the author refers   
      to in his final paragraph are just what we'd expect from conservation   
      of energy, given the mechanical work the dancer is required to exert   
      to pull her arms in.   
   -- jt]]   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)