Peeter Joot's (OLD) Blog.

Math, physics, perl, and programming obscurity.

Proof that the conservation of energy is wrong. Not!

Posted by peeterjoot on January 25, 2012

My dad asked me about a website that claims to have a proof that the conservation of energy is wrong. The author, as part of his argument asks

“what exactly has the kinetic energy of the second rocket’s two burns been transformed into?”

My response to my dad was:

There’s lots of things that the burns have been turned into. He demonstrates an impressive lack of understanding of not only physics, but chemistry. In the chemical reactions that expel the exhaust particles, there’s lots of heat and light produced, both of which carry out energy from the ship. The other thing that is glaringly obvious is that he doesn’t even consider the exhaust itself.

Rockets are a very primitive devices and they actually propel themselves by tossing bits of themselves out the back. You could do this if you could put yourself on a very frictionless surface, along with a very heavy mass. If you toss the mass in one direction, you’ll end up moving in the other direction because momentum of you plus the mass have to be conserved. Perhaps you could actually do this experiment. Get a big rock and a dolly and put the dolly on ice with you and the rock, and then toss the rock. You should move in the opposite direction. Rockets expel most of their mass doing this, with chemical reactions making that expelled mass move much faster so that they gain they momentum (in the opposite direction) of the exhaust they expel. It’s the rocket, plus its exhaust, plus all the light and heat changes that occur in the chemical reactions that have to be considered if you are looking at conservation of energy.

Basically, the guy who authored this page appears to be talking out of his ass.  I’d like to try the experiment that I outlined for my dad.  Since it is winter time, perhaps I could just put on my ice skates and find something big to throw in front of me.  I should move backwards a bit in response.


One Response to “Proof that the conservation of energy is wrong. Not!”

  1. Eli Lansey said

    I’ve actually been thinking that instead of / in addition to the standard bank of undergraduate physics problem sets, a better (and more fun) sort of question would be:
    “Check out this thing I found on the Internet or Are they right or wrong? Why?”

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