http://www.npr.org/2011/09/10/140361610/nasa-launches-probes-to-study-moon describes a recently launched unmanned NASA mission to the moon to map out the moon's gravitational field. What is the gravitational field? It's quite simply the acceleration due to gravity ("g" as we've been calling it in class) as a function of position around the moon!
On the surface of the earth, g is a pretty consistent 9.8 m/s^2, but it does vary depending on your position on the planet, since Earth is not a perfect sphere. And once you start to get out into space, g begins to diminish drastically, dropping off like 1/r^2, where r is the distance between you and the center of the earth!
The moon's acceleration due to gravity behaves much the same way. On the surface of the moon (at least the parts we've been to!), it's about 1/6 of our g on earth (so about 1.7 m/s^2, give or take), and also drops off like 1/r^2 (where r is the distance between you and the center of the moon) as you leave the surface.
These probes will measure these variations in the moon's g as they orbit on opposite sides of the moon! By the way, the GRACE mission (http://www.csr.utexas.edu/grace/) did the same thing on earth! Here's a map of the results, depicting the difference between the local g and the average g: http://www.csr.utexas.edu/grace/gallery/gravity/03_07_GRACE.html, where the red regions represent a higher value of g and the blue regions represent a lower value of g (measured in units of "milligals," which are named after Galileo; 1 gal = 1 cm/s^2).
I can see on the earth, with the example of the gravitational fields that there are some areas on the earth where the fields are much stronger. I would imagine that the greater mass you have under your feet, the more you way. So theoretically would you weigh more on a mountain than you would at sea level? Also why is the gravitational field stronger around the "Pacific Ring of Fire", than anywhere else?
ReplyDeleteWell, remember that the gravitational force also depends on the distance between you and the mass that's attracting you. Specifically:
ReplyDeleteF = G m1 m2 / r^2,
so the closer you are to the earth, the greater your gravitational force!
I find it fascinating that the areas that, like Jordan said, have the highest gravitational pull are the areas around the Pacific Ring of Fire... however, I have to combat what he said about standing on top of a moutain. Using the formula "1/r^2" and noting this is how much gravity "falls off" as you travel further away from the center may explain why the gravitational pull is greater in this region- these areas are obviously have the most volcanic activity, thus one could possibly surmise that these are the "lowest" points on the earth, thus they are closest to the physical center of the earth, making their gravitational pull slightly greater than those felt, say, here in Florida...
ReplyDeleteI wounder how far you would have to be off the Moon's surface to float off into space? When you see footage from the moon w/people running around, they seem to bounce about a foot into space w/ every step, so it'd be fun to see how much force it'd take someone to float off.
ReplyDeleteBen: There's an xkcd comic for everything!
ReplyDeletehttp://xkcd.com/681/
Full-sized image at http://xkcd.com/681_large/.