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Re: [Phys-L] Moon's orbit



The simple answer is that the sun's pull is what keeps the moon in the 93 million mile orbit around the sun while the earth's pull is what keeps the moon the the quarter million mile orbit around the earth. I'm sure the situation _is_ more complicated in detail, but for HS (for my intro classes too) the simple explanation that the two forces are involved in two different orbital motions should suffice.

rwt

On 10/17/2016 9:58 PM, Anthony Lapinski wrote:
The Sun pulls on the Moon with about twice the force that the Earth pulls
on it. So why doesn't the Moon get pulled away from the Earth? I realize
this is complicated. Is there a "simple" explanation I can tell high school
students?

I searched online. One site said that the Moon's orbital velocity (1 km/s)
is simply less than the Earth's escape velocity (1.2 km/s) at the Moon's
distance from the Earth. Not sure how they came up with this 1.2 number.

Several sites mentioned the Hill sphere (never heard of this before). I
guess if an orbiting object is within a certain distance of a central body
(e.g., Earth), the gravity dominates that from a more distant body (e.g.,
Sun). Is this related to the Roche limit?
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