Wednesday, 21 January 2015

newtonian mechanics - Will an object falling into Earth's orbit start spinning?


Assume an object falls towards Earth (I've drawn a hyperbolic orbit, but this would apply to any orbit). The object starts at $A$, and at this point it is not rotating i.e. an observer on the object would measure no fictitious forces. Will the object rotate as it passes the Earth and moves away?


My Newtonian intuition tells me that the object will not rotate so we will see all sides of the object depending on its orbital position. This is because the object had no spin prior to orbiting Earth. The motion through the orbit would look like:


No rotation


My Einsteinian intuition tells me that the object should "rotate" from our perspective because it's following the curvature of space and it is moving in a straight line. The motion through the orbit would look like:


Rotation


Which one is correct, and why?




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