How can both fission (in nuclear power plants and nuclear weapons) and fusion (in the sun) release energy? Surely they

Question: How can both fission (in nuclear power plants and nuclear weapons) and fusion (in the sun) release energy? Surely they are the opposite of each other, so one would have to lose energy to avoid perpeual motion, where you decay an atom and then repair it endlessly, gaining energy each time?
- Keywords:
  decay,
  fission,
  fusion,
  perpeual
Asked by bridget to Amy, Drew, Sara on 23 Jun 2011.
- Drew Rae answered on 23 Jun 2011:
  
  Hi Bridget. Your question makes sense – if we fissioned (is that a word) and fusioned the same elements we wouldn’t gain anything. So what we do is pick the reactions from each which are easiest and give the most energy.
  
  Fusion we would fuse hydrogen to get helium. Fission we use Uranium 235 or Plutonium. So they are quite separate reactions. We couldn’t put the helium we get from Fusion into a Fission reactor – it takes energy to break up helium, it doesn’t give us energy.
- Amy MacQueen answered on 23 Jun 2011:
  
  you have really well thought out questions Bridget!
  
  I must confess that I am not an expert in the fission/fusion field but that as far as I understand it Drew is right – it depends on the atom type whether fusion or fission will give you the most energy. As for perpetual motion is that not when a reaction produces more energy than it consumes (whether or not it is indefinite?)…these are believed to be impossible right? (cause they would break thermodynamics laws).
  
  I know this is horrifically simplistic (and probably grossly unscientific!!) but if you snap a carrot in half you get sound released and if you bang two peppers together hard enough so that they stick together you also get sound released. They are both vegetables that you are causing to make sound by different ways – one by smashing together and one by breaking apart but you wouldn’t try and force the carrots together because it really wouldn’t work, or snap the pepper in half because it would be harder to do – you choose the vegetable appropriately to make the sound!
  
  Okay so now I am waffling…maybe I should go check that its really possible to smash two peppers together so that they fuse…
  
  🙂

Question: How can both fission (in nuclear power plants and nuclear weapons) and fusion (in the sun) release energy? Surely they are the opposite of each other, so one would have to lose energy to avoid perpeual motion, where you decay an atom and then repair it endlessly, gaining energy each time?

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