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Physics/Orbital mechanics


Merry Christmas,

If an exterior force moved the earth into a smaller orbit without affecting any other thing at all regarding the earth, and then that force disappeared, what would the earth do ?  

Bounce back to its original orbit size due to gravity equilibreum ?  Remain in the smaller orbit but moving faster due to a shorter orbit length ?


An exterior force could not change the radius of an orbiting object without changing other things. If you apply conservation of energy and of angular momentum rigorously, you'll find the only way to move our Earth into a smaller radius is by changing its orbital velocity.

According to
a force applied to an orbiting body, perpendicular to its orbital velocity, would change the eccentricity of the orbit, but not the orbital radius. A force applied along the line of orbital motion would change the velocity and eccentricity, but not the radius.

Unfortunately, your question is like asking what would happen if magic elves changed the radius of our Earth's orbit, but nothing else. The answer is we don't know the effect of magic elves.

As I have not studied orbital mechanics in detail, this is all I can answer on this topic.


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I can help with understanding physics that does not involve eggs. I will NOT help with academic or professional questions, which are NOT limited only to homework. Please do not waste your time by asking a question that comes out of ANY kind of academic, professional, or business matters.


Have been fascinated by physical laws ever since I learned, at age seven, that magnets work under water. My study continued through college and has not ceased even after I retired.

B.A. in Physics (with honors) from University of California at Berkeley.M.A. in Physics (with honors) from University of Texas Austin.

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