1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

If the moon suddenly vanished, what would people on earth experience?

  1. Apr 16, 2008 #1
    Would there be earthquakes and tsunamis, or would nothing odd happen at all apart from smaller tides?
    Last edited: Apr 16, 2008
  2. jcsd
  3. Apr 16, 2008 #2
    The earth would wobble like crazy. The seasons would be all out of whack. Life wouldnt survive for long.

    No tides either.
  4. Apr 16, 2008 #3
    I agree with your last point, no tides at all.

    but no life ? surely the moonlight brings the ladies into a romantic mood and makes it easier to seduce them (not that I would claim too much expertise here...), so:

    no moonlight -> no seduction -> no sex -> end of mankind

    but surely the animal kingdom as a whole should not be affected ?

    seriously, as for the wobble: OK, moon and earth are kind of synchronized, but I always thought this would mostly affect the moon (rotation about its own axis in sync with rotation around earth, therefore always pointing same side to us), but would earth really be affected that much ? no stable rotation around our own axis any longer ?
    Last edited: Apr 16, 2008
  5. Apr 16, 2008 #4
    We would only know about it a few seconds after it happened! :smile:
  6. Apr 16, 2008 #5


    User Avatar

    Staff: Mentor

    Why would the earth wobble?
  7. Apr 16, 2008 #6


    User Avatar
    Science Advisor

    There would still be tides, I think, only due to the sun's gravity, therefore much weaker and slower, than the lunar tides we experience. I don't remember what I read, but I seem to recall something detailing how our moon is actually extremely important to the development of life on Earth.
  8. Apr 16, 2008 #7


    User Avatar
    Gold Member

    I've never heard of that, but it might make sense if low tides made it easier for our ancestors to transition from the ocean to land.
  9. Apr 16, 2008 #8
    I'm thinking that if the earth has a force pulling on it constantly and then that force is suddenly removed, you'd get vibration as the earth relaxed into a non-stretched state, like a rubber band vibrates after it's shot. Maybe that means huge earthquakes and tsunamis. I don't think the earth would wobble, just vibrate.

    The tides allowed sea animals living near the shore to be exposed to air for periods of time as they were left in the sand as the tide went out. That would acclimatize them over time to land life.
    Last edited: Apr 16, 2008
  10. Apr 16, 2008 #9
    So it wouldnt wobble? more than it already does, anyway.
  11. Apr 16, 2008 #10


    User Avatar
    Science Advisor

    Erm, I see no reason why the earth should suddenly feel a "spring force". Simply, the earth has two forces on it right now: due to the sun and moon. If the moon disappears we will simply accelerate due solely to the sun. There is no "resting position" for the earth that the moon took us out of...
  12. Apr 16, 2008 #11
    The gravitational force the moon exerts on the sun is approximately half that of the sun. The axis is tilted and so they both torque the Earth causing it to precess. With the moon gone there is no partial cancellation of the torques and so the net torque will be greater, and thus the precession will be greater.

    That's just speculation from me, I don't really know what I'm talking about.
  13. Apr 16, 2008 #12
    There would be no Earthquakes! The moon is 80 times lighter than the Earth and it's distance from the Earth is about 50 times Earth's radious. This gives only 1/200000 g of acceleration. In addition the Earth is deformed only by gradient of that gravity, since it is in free fall motion against the Moon: each atom on Earth is atracted with almost the same force as needed to maintain radial acceleration. If you remove both force and acceleration, then nothing happens (except the very small effect, because the near end of the Earth used to experience more attraction than the far end).
  14. Apr 18, 2008 #13
    we would have less light pollution at night for observing with telescopes. We would have no more Lunar or Solar Eclipses.
  15. Apr 18, 2008 #14
    We will no longer have 24 hour per day. It will be much faster. I could not recall the exact number. Anyone can help?
  16. Apr 18, 2008 #15
    If the Moon would vanish, we would still have 24 hours per day, since Earth's rotation frequency is determined by it's angular momentum. As far as the length of the day is concerned, Moon's dissapearance would be an advantage, since the torque of Moons gravity would cease and the rotation would not slow down anymore.
    But if there was no Moon in the history of the Earth, then the Earth would still rotate very fast and the life on Earth would probably be very different.
  17. Apr 18, 2008 #16
    If the moon vanished, NASA would get blamed, and it would turn out that there was never any moon at all, just a government conspiracy so NASA could fake the moon landings.
  18. Apr 18, 2008 #17
    ooops.... seems that my statement "no tides at all" was quite wrong. after some calculation I think that they would not even decrease that much:

    if we have a mass M, then a test mass in the distance r would experience an acceleration of

    a(r) = -GM / r^2

    to get the gradient, which is the cause of the tidal forces, we have to differentiate this and get

    a'(r) = 2GM / r^3

    now we are not interested in absolute values, but in the relative strength of the tidal forces from moon and sun. so 2G cancels and we get as the relation

    (Ms / Mm) * (rm / rs) ^ 3

    where Ms and Mm are the masses of sun and moon and rm and rs are the the distances earth-moon and earth-sun.

    putting in the numbers I get the result that the tidal forces of the moon are only stronger than those of the sun by a factor of 2.18

    so the tides would decrease significantly, but they would not at all vanish !

    these are the numbers I used:
    Ms = 1.9891 E 30 kg
    Mm = 7.3477 E 22 kg
    rs = 1.496 E 11 m
    rm = 3.84399 E 8 m
    Last edited: Apr 18, 2008
  19. Apr 18, 2008 #18


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    LOL...a government conspiracy somehow passed along amongst all world governments that have ever existed anywhere throughout recorded history. I'm impressed! I wonder how they pulled off the mass hallucinations...
  20. Apr 18, 2008 #19
    So that bright ball I used to observe on the sky was actually a product of my brain implant?
  21. Dec 15, 2010 #20
    No doubt about that! Haha
  22. Dec 15, 2010 #21
    Should the moon vanish there would be less of a gravitational force being applied to the Earth as well as its inhabitants. As for the tides, they would still exist (due to the sun's gravity) however to a much less of a degree.
  23. Dec 16, 2010 #22


    User Avatar
    Gold Member

    It would also mean the extinction of werewolves, and then where would I be?
  24. Dec 16, 2010 #23
    The Gravitational pull would be from the sun only. therefor we would only have 1 high tide and only at or about noon everyday. the lowest low tide would be on or about midnight.
    there would be effects on the animal kingdom as it would disrupt them to veritable degrees
  25. Aug 3, 2011 #24
    if moon suddenly disappears ,then as we know weak and slower tides will be there,we will have faster rotation due to absence of gravitational force on earth, which consecuently increase and resizes earths radius resulting in slower angular velocities.also the trajectory of earth might change if this act of disappearing takes place when earth is not on the earth moon,solar oribit.as we know the orbit that we speak of around the sun is not earth's orbit,but orbit of earth-moon system.as earth and moon both revolve around each other,hence many a time earth is not on it's actualy trajectory.but it is the moon that brings it back to it's path.so in such case ,earth will not be influenced by any such force and hence it's trajectory will change.this will create havoc in all our seasons.also depending on the time of disappearance of moon,avg temp on earth may reduce or increase...
  26. Aug 3, 2011 #25
    I have to admit, I made a error in this statement.

    With only the sun to create tides. Noon and midnight would be the high tides. 3 and 9 would be the low tides.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook