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!

Ineresting thought on earth's speed and rotation.

  1. Aug 29, 2010 #1
    Let me give an example to make it short and clear - suppose we want to travel from China to US i.e east to west . We know that earth rotates from west to east. Now if we could only manage to hang in the space(like hovering helicopter) just few hundred meters above the ground without actually moving , then the surface below would move due to earth's motion from west to east and we could be in US or let's say US will come below us just in about 8 hours without actually moving on our own. This might make it virtually possible to travel from any one place to another in earth in not more than 24 hours by just hanging on air.

    Well there may be some objection on it that even if it is possible , due to certain degree
    inclination of earth's axis, we might travel in an spiral motion and we might not exactly end
    up in US or desired location. This could be solved by making a short vertical displacement relative to earth's latitude. But that is not my main matter of concern. I am actually wondering if earth would move relative to us if we were hovering is air. Let's reduce the example to origin place just below equatorial plane and destination just above it so the scenario might get closer to possible.

    Well we might have some obvious answer like
    1)Since we are in earth and it is very large compared to us so we cannot feel the movement of earth and of course we cannot travel relative to earth.

    2)It doesn't matter if we are in ground or air , in ground we will be moving along with ground and in the space above the ground , we will move along with the space which is turn is in the earth's atmosphere and atmosphere of earth is moving along with earth.

    3)Everything in earth is moving in same speed including atmosphere and like such....

    But still there are some points that keep me insisting that this phenomena is actually possible.

    1)There was an TV program where it was shown that a long pendulum that started to swing in one direction in morning and kept on swinging throughout the day , finally ended up swinging in different trajectory at the end of the day inclined at a certain angle to the original path. This may make it clear that the movement of earth has some relative impact on objects.

    2)Why can't we feel inertial effects on us due to earth's movement or are we actually having it but we are so adapted to it that we can't feel it?

    3)I simply believe that this is possible.

    I am just wondering if this phenomena is actually possible and it is being used in flight routes scheduling , in hovercrafts or it isn't possible or it is possible but has not been implemented yet.

    I would like to leave you with another short question at last. If a basketball was dropped from a height of 10 km exactly above the center of a basketball court on earth's surface, would it fall in the center or somewhere else . Lets assume that it takes 10 minutes for ball to hit the ground and lets neglect the effect of air resistance or air flow for this case.

    I am anxiously waiting for your thoughts/replies/solution over this matter. I would love to share much more interesting thoughts that I've got related to this matter in future when I get your opinions.​
  2. jcsd
  3. Aug 29, 2010 #2
    Good questions! However, they have all been answered long before you or I were born.
    I will leave it to the experts to expound further.

    To tease you somewhat, consider this scenario:
    Your an astronaut in the International Space Station(ISS). You and the ISS are moving at more that 17,000 mph. You decide to jump-up.

    Will that cause a problem? That is, will the inside back of the ISS slam into you at 17,000 mph?
    If the inside of the ISS were a total vacuum and you did the same jump, would it be any different?
  4. Aug 29, 2010 #3
    Yeah nice point there. Now, that we know that an astronaut can't feel or experience the movement of ISS in vacuum as well, we can say that it wasn't the atmosphere of earth doing the trick.

    So this brings us down to two possible reasons for we not being possible to experience the movement.

    1)Inertia. Like we don't feel movement traveling in a plane or train moving at constant velocity. Also, an object projected from a moving body moves at the same velocity as that of moving body like a satellite launched in space from rocket.

    2)Surrounding- atmosphere in case of earth and ether in case of space/vacuum. that moves the object within along with it.

    Now considering the fact that it also happens in vacuum and it isn't the atmosphere of earth dragging us along a few more question arises.

    1)Is the atmosphere of earth steady/static or moving along with the earth?

    2)If it is steady then why don't we feel resistance due to the air around us cause we are moving along with the ground at almost 1000mph along the equator and about 100 mph in places near the poles. We must be facing a hurricane that has barely 80 mph speed anytime considering we are moving at a high speed into a static atmosphere.

    3)If the atmosphere is moving then why don't we fell different resistance while moving in different direction in ground or in air like that we feel different forces while moving into the wind and away from wind. We know that earth is rotating at more than around 1000mph along the equator and we can easily feel the wind having speed 20mph. So that means that we must feel a lot more resistance due to air while moving from east to west (ie opposite to direction of earths rotation) than from west to east (ie along the direction of earth's rotation.)

    I would like to have some replies from experts regarding this matter but I would still highly appreciate different kind of thoughts or opinions from all the viewers.Just express whatever you think about it.

    Again, thank you for your point 'pallidin'.
  5. Aug 29, 2010 #4
    It's called Foucault's Pendulum and its based on precession and gyroscopic effects, which I lack of knowledge in that, but if I remember right the pendulum will maintain a constant direction if it is held in the equator.

    Relative velocities. Suppose Earth rotates at your 1000mph, and you move westward at 20mph, then your actual velocity (as seen from the outside) is 980mph, and if there is no wind then you would only feel 20mph wind. But if there is 20mph wind eastward then you would feel 40mph wind, because the wind is actually traveling at 1020mph and you at 980mph.

    I'm not any kind of expert but hope this helps.
  6. Aug 29, 2010 #5
    What about using a long cable from the moon to anchor a holding station? Yes, you would have to get people on board it using some kind of high speed vehicle, but maybe some kind of pendulum motion could slow down the interface between the station and loading vehicles. Once passengers were on board, they could travel halfway around the world in 12 hours, right? But how much cable would be needed and how strong would the cable have to be to withstand the forces? It might be more efficient to just mine a tunnel through the core and use the metal for something else.
  7. Aug 29, 2010 #6
    Doubt that mining through the core, if it is even possible, would be more efficient than anything. Comfy sauna down there :tongue2:
  8. Aug 30, 2010 #7


    User Avatar
    Homework Helper

    There are a couple of reasons you can't just jump up and "hover" while the Earth moves under you. Basically inertia and gravity. That is, when you lose contact with the Earth's surface, you'll keep moving sideways (in the direction your piece of the Earth was moving) at the same speed, say 1000mph at the equator. If it weren't for gravity, you'd fly off in a straight line, but gravity pulls you back down to Earth.

    The atmosphere does rotate along with the Earth, by the way.
  9. Aug 30, 2010 #8

    Thank you for letting me know that it was actually some kind of experiment. Are you sure that the pendulum will move in a constant direction if in equator. I just feel that this may not happen as equator is not perpendicular to earth rotation axis or may be there's some other reason and you are true. I also don't know too much about it. Let me know if you are sure of the reason.

    For relative velocities , I was a bit unclear about how you calculated the speed of us being 980mph moving east to west at 20mph. I think if looked from outside then our velocity would be -980mph, as if we are moving along the earth west to east though trying to move 20mph forward.

    But anyways thank you for your concern and interest in the topic. Hope you will help solve out the quest.
  10. Aug 30, 2010 #9

    Oh that was among the brilliant idea I have ever heard. Though it my not be practically possible but still we can not neglect the possibility. Sure enough if we could create such long cable and holding station in the end then it would really be interesting to view the space in a swinging swing in space.Feels great to think about it , let's hope we get it made some day.

    And by the way if we could mine a tunnel through the core then we might have really good experiments to perform on the tunnel rather then using the molten metal mass for making a cable. Don't you think so?
  11. Aug 30, 2010 #10

    Well that might be the real reason but still it is the same that I don't understand how it works?
    Ok lets assume that we are actually going against the earth direction of motion ie at 1000mph in a plane just after the take off. So does that makes us stationary and if were to travel in the same direction as that of earth's then we might be travelling at twice the speed with same power. Please make me clear if you can. Thank you.
  12. Aug 30, 2010 #11
    This thread raises an interesting parallel question:

    If objects on Earth's surface have a certain rotational momentum that pushes them against gravity like a centrifuge, do they experience more gravity when traveling in the opposite direction as the spin and less when traveling in the same direction.

    E.g. If the Earth is rotating at 1000mph and a jet is flying 1000mph against the spin, would it be pulled down with greater force and, likewise if it was flying fast enough in the other direction would it's momentum overcome gravity? Put another way, why is orbital speed the same in all directions instead of be faster in the anti-spin direction if there is a centrifuge effect due to rotation?
  13. Aug 30, 2010 #12


    User Avatar
    Gold Member

    Yes it is, by definition.
  14. Aug 30, 2010 #13


    User Avatar
    Gold Member

    Objects moving 1000mph clockwise wrt to an inertial frame of reference will experience a "centrifugal" effect exactly as much as objects moving 1000mph counterclockwise. Objects not moving will experience no centrifugal effect at all, and will weigh more.

    The above is true completely independent of Earth's rotation. It is only complicated once you start using the (moving) Earth's surface as a reference point.

    Yes. That's why, when rockets blast off from Cape Canaveral, they always head East. Heading East gives them at ~1000mph free boost to orbital velocity.
    If rockets launched Westward, they would have to gain 2x ~1000mph under their own power.

    (There are no launch facilities on the West coast. It's a bad idea to launch them out over inhabited land, and since all rockets head eastward, East Coast it is.)

    Orbital speed would not normally be calculated with reference to ground-speed. Usually some external FoR would make more sense.
  15. Aug 30, 2010 #14
    You sort of touched on it when you mentioned the shuttle launches, but the question is when the centrifugal effect of an object rotating with the Earth becomes independent of the rotating Earth as its FOR. Yes, relative to everything else rotating with it, such as the atmosphere, any flying object experiences the same centrifugal effect. But if stationary objects on the ground experience a certain amount of centrifugal momentum due to Earth's rotation, then that should remain the case when they leave the ground as well, right? So a helicopter or hot air balloon traveling straight up must actually weigh less than it would if the Earth stood still, right? So if it is moving in the opposite direction as Earth's rotation, why wouldn't it gain weight?
  16. Aug 30, 2010 #15


    User Avatar
    Homework Helper

    Yes, if you look at it from an inertial frame of reference, you're right. A plane traveling with the Earth's rotation at 1000 mph with respect to the Earth would be going at 2000 mph with respect to the inertial frame of reference, and a plane traveling against the Earth's rotation would be stationary in that inertial frame of reference. (Technically: a frame that is as close as you can get to inertial, given that its origin is attached to the center of the Earth)
    I think you're right, although you're misusing some terms so I can't be sure (e.g. there's no such thing as "centrifugal momentum" as far as I know, I'm guessing you mean "centrifugal force"). But anyway, if you were moving against the Earth's rotation at 1000 mph, in principle I think you would have a larger apparent weight than if you were standing on Earth's surface. The difference would be pretty small, though. You can actually calculate it and find that it's barely detectable, it's maybe around 1 percent or less of the force of gravity IIRC.
  17. Aug 30, 2010 #16
    Yes, Foucault's Pendulum will stay in one plane at the equator. Look up Wikipedia for details on how it works. Basically, the rate of rotation tells you your latitude.

    As for motion of Earth and its actual effects, notice that rockets are launched heading East and near the equator. In fact, Jules Verne picked the same place as NASA did for the space center, for sound reasons.
  18. Aug 30, 2010 #17


    User Avatar
    Gold Member

    Surely the rate of rotation is the same at any non-zero latitude, to wit: 360 degrees in 24 hours.

    [EDIT] Nope. Apparently not.
  19. Aug 30, 2010 #18

    In the second section of the Wikipedia article (that is, after the introduction) it states that it is proportional to the sine of the latitude. Then it explains why.

    It is certainly not discontinuous! I don't know what you are thinking of. The behavior changes smoothly as you move from one position to another.
  20. Aug 30, 2010 #19
    Not true at all(just to be picky)
    Vandenberg Air Force Base, located in Santa Barbara county, CA.
    They launch all sorts of stuff into space, and the trajectory goes over the continental US towards the east(military and commercial satellites). The exception are pacific ocean missile defense tests, which trajectory to the west over the pacific ocean.
    Last edited: Aug 30, 2010
  21. Aug 30, 2010 #20


    User Avatar
    Gold Member

    I did not know they launched stuff.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook