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Q & A: What kinds of energy are associated with the earth-moon system?

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Most recent answer: 05/14/2014
What kinds of energy are occuring when the moon is orbiting the earth? I know there is heat energy because heat is the result of everything but where does it come from?
- Jake Wider (age 14)
Gig Harbor, Washington, America

Hello Jake,

There are two kinds of energy associated with the earth-moon orbital system:  kinetic and gravitational.   Kinetic energy is usually written, with slight corrections, as EK = 1/2 Mmoonv2 where v is the orbital velocity of the moon .The gravitational energy is  Eg = -G Mmoon Mearth/ r, where G is Newton's constant and r is the earth-moon distance.   The total energy Etot = Ek + Eg is a constant.  The lunar orbit is a bit eccentric and so the earth-moon distance changes.  The gravitational energy changes a bit but the orbital kinetic energy changes just enough to ensure total energy conservation.  

  If for some reason the moon should crash into the earth all of that energy would be transferred into heat and kinetic energy of the debris flying off with catastrophic consequences . 



p.s. You may also be interested in this old post about how energy gets traded between the Earth-Moon orbit and other modes, especially the Earth's rotation and simple heating of the Earth: .  Mike W.

(published on 05/14/2014)

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