Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Why do we rotate along with the earth?

  1. Sep 14, 2012 #1
    Do we rotate along with it because of it's gravitational pull? Or is it friction?
     
  2. jcsd
  3. Sep 14, 2012 #2
    Why do you accelerate together with a moving bus while standing in it?
     
  4. Sep 14, 2012 #3

    Drakkith

    User Avatar

    Staff: Mentor

    Well, we are already moving with the Earth, friction allows us to accelerate in any direction without sliding and keeps us in place, and gravity keeps us pulled down to the surface.
     
  5. Sep 14, 2012 #4

    russ_watters

    User Avatar

    Staff: Mentor

    I prefer the second answer: we have always been moving with earth, so neither friction nor gravity are required to keep us moving with the earth.
     
  6. Sep 14, 2012 #5

    A.T.

    User Avatar
    Science Advisor
    Gold Member

    The OP asks about rotation along with the Earth. You can go to the North Pole, rotate slowly againts the Earth's spin, and you are not rotating along with the Earth anymore. So you cannot generally say that everyone has been always rotating with the Earth.
     
  7. Sep 14, 2012 #6

    vk6kro

    User Avatar
    Science Advisor

    We need both.

    If we had neither, we would be attracted towards the sun which, presumably, would still have gravity.

    If we only had gravity, we would watch the slippery earth moving underneath us, but we would remain stationary.

    If we only had friction, we would be projected tangentially away from the earth into space.
     
  8. Sep 14, 2012 #7

    russ_watters

    User Avatar

    Staff: Mentor

    Ok, almost everyone -- 99.99999% of the population (estimate).
     
  9. Sep 14, 2012 #8

    russ_watters

    User Avatar

    Staff: Mentor

    Stationary wrt what?
     
  10. Sep 14, 2012 #9

    vk6kro

    User Avatar
    Science Advisor

    With respect to the center of the earth.

    Instead of being rotated, we would just be dragged towards the earth by gravity, but we would be unable to penetrate the earth, so we would just cling to the outside, but not rotate with it.

    It would be a fairly terrifying existence as we would be unable to even drill holes in the earth to get a grip on it because it was moving so fast.
    I saw a calculation that gave the speed of the earth's rotation, at the equator, of 1070 miles per hour or 0.297 miles per second.

    Good question.
     
  11. Sep 14, 2012 #10

    russ_watters

    User Avatar

    Staff: Mentor

    Again, all that assumes we are placed on earth stationary wrt its rotation.

    The reason I consider this caveat important is that in our daily lives, friction does not play a role in keeping us rotating with the earth. Most people asking such questions seem to think that if friction suddenly disappeared, we would start being left behind earth's rotation.

    ....unless we move significantly north or south, as per A.T.'s point.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Why do we rotate along with the earth?
  1. Why do we assume this? (Replies: 11)

  2. Why do things rotate? (Replies: 26)

Loading...