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Would a very tall building bend due to the Earths rotation?

  • 10-04-2015 8:40am
    #1
    quenching
    Registered Users, Registered Users 2 Posts: 1,190 ✭✭✭


    After building a tower in Minecraft my 10 year old asked a question I'm finding hard to answer:

    Would a building build on Earth and extending past the atmosphere into space stay straight or bend due the the rotation of the earth?


    We assumed we had a material strong enough to build such a tall structure.

    Also, same query but on an Earth that didn't have any atmosphere?


Comments

  • #2
    ScumLord
    Registered Users, Registered Users 2 Posts: 28,789 ✭✭✭✭ScumLord


    I would assume it would be pulled straight, I don't think it would bend. It would be the same as the example of swinging a ball at the end of a string. The centrifugal force would be pushing the ball away from the centre.


  • #3
    Capt'n Midnight
    Moderators, Recreation & Hobbies Moderators, Science, Health & Environment Moderators, Technology & Internet Moderators Posts: 93,596 Mod ✭✭✭✭Capt'n Midnight


    For very long suspension bridges the towers may be a few cm out of alignment because of the curvature of the earth.

    and the main force on skyscrapers is wind loading , if they can survive a hurricane they can probably stand up to their own weight

    and yes they do sway a bit , and some have dampening mechanisms to cancel the sway



    but out side the atmosphere they would stay straight because they'd keep going at the same speed , no wind or anything to change that. very far out there'd be problems with the moons gravity like the way it does tides and stuff , but getting hit by satellites travelling at 8Km/s would be a more immediate concern

    if you make them really tall then you have space elevators , the top then travels at geosynch orbital speed so just stays there , if you make them really really tall then you can fling stuff off into space , 'cept the moon would get in the way by then


  • #4
    dlouth15
    Registered Users, Registered Users 2 Posts: 1,169 ✭✭✭dlouth15


    It would bend.

    If you consider a building on the mid-latitudes somewhere between the equator and the poles, two forces contribute to what we feel as gravity. There's gravity proper which acts towards the centre of the Earth and there's the centrifugal force which acts away from the axis of the Earth.

    When we build a skyscraper upwards, the "up" here means opposing the combined effect of these two forces. "Down" likewise means the combined direction of the two forces.

    The key point is that they don't act along the same line. As the building gets taller, gravity gets weaker and the centrifugal force gets stronger but as they don't operate along the same line, the combined direction changes. Thus a building built straight up, unless it is either on the equator or on the poles, will be subject to stress causing it to bend.


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