Math Is Fun Forum

spoiledlori

Member

Registered: 2008-07-08

Posts: 4

moons orbit

question:
Find an approximate value for the rate in which the moon orbits the earth. Assume the moons orbit is circular.

Thanks for all your help in advance...i haven't a clue qhere to begin

gnitsuk

Member

Registered: 2006-02-09

Posts: 121

Re: moons orbit

By the rate at which the Moon orbits the Earth do you mean it's speed along it's orbit?

If so, you can look up the Moon's distance from the Earth's centre (call it r - in miles say) and the time it takes to complete one orbit (call this t - in hours say).

The the distance travelled by the moon in one period is the circumference of a circle of radius r = 2*PI*r

and the speed (v) is then equal to:

2*PI*r / t    (units of miles per hour).

John E. Franklin

Member

Registered: 2005-08-29

Posts: 3,588

Re: moons orbit

Moon is about 1/4 million miles away.
Goes around about 28 days.
So pi is about 3
So 3/4 million miles around in 14 days.
That's about 2 million miles in 37 days.
Now what is the reciprocal of 3.7 ???
37 )______
37 )  100
   2 x 37 = 74, so 26 left over.
   So 100/37 = 2R26
       ______
37 )  260
    7 x 37 = 259, woah close one.
So we're done.
1/3.7 = 0.27 about.

So the moon goes about 27,000 miles in a 12 hours around us, neglecting
us moving around the sun.
27000 / 24 = 1125 miles in half an hour if I didn't mess up in my head.
1125/3600 will get you miles in half a second if want it.
I messed this all up since I forgot 6 radiuses is the perimeter, at
first I did 3 radiuses, so I corrected it fast.
These are all estimates since pi = 3.14159265358979323846...
and 1/4 million miles is an estimate too.

Last edited by John E. Franklin (2008-07-10 09:57:25)

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