Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: [Phys-L] Moon's orbit



Hmm... where would the Sun pull the Moon away to? Both the Moon and Earth
are currently in freefall toward the Sun, so they're both being pulled to
the Sun. Suppose we could turn off the Moon-Earth interaction. We could
arrange to have both Earth and Moon in the same orbit around the Sun, one
behind the other. So even with zero pull on the Moon by the Earth, there's
no need for the Moon to get pulled "away" by the Sun.

On Mon, Oct 17, 2016 at 9:58 PM, Anthony Lapinski <alapinski@pds.org> 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?
_______________________________________________
Forum for Physics Educators
Phys-l@www.phys-l.org
http://www.phys-l.org/mailman/listinfo/phys-l




--
Carl E. Mungan, Professor of Physics 410-293-6680 (O) -3729 (F)
Naval Academy Stop 9c, 572C Holloway Rd, Annapolis MD 21402-1363
mailto:mungan@usna.edu http://usna.edu/Users/physics/mungan/