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Thread: a question

  1. #1 a question 
    Forum Freshman
    Join Date
    Mar 2009

    I'd like to know the answer to this question please

    If say, a canonball, were taken into space and then 'fired' directly at the centre of the Earth, as it entered the Earths gravitational field would it's tradjectory travel directly toward the centre of the earth (on a straight path until it struck the surface of course) or would it begin to rotate with the Earth as it travelled creating a curved tradjectory (assume that the canonball is completely unnafected by any interaction with the atmosphere!)

    I realise that there are all sorts of Relativistic and reference frame answers to this, but I'm looking for the 'simple' answer.

    Thanks in advance


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  3. #2  
    Moderator Moderator Janus's Avatar
    Join Date
    Jun 2007
    Assuming that the cannon was not already circling the Earth in sync with the Earth's rotation, then the cannon ball would come straight in for all intents and purposes.

    The last little caveat is because there is a General Relativity effect called Frame Dragging, where the rotating mass tends to drag space with it. However, this effect is very very weak, and would only alter the cannon ball's trajectory by a vanishingly small amount.

    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone

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