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).
Wow, that is really interesting. I had no idea that our gravitational field had spots of weaker and stronger "g". From what I was always taught we just assumed that gravity was consistent, and I never questioned that there would be fluctuation in gravity especially since the Earth isn't a perfect sphere. Of course, we normally do theoretical physics which is why we ignore the fact that there is fluctuations in the earths gravity. That's why I prefer theoretical physics. Experimental physics has too many variables that skew our results.
ReplyDeleteGreat points, Elamon!
ReplyDeleteWhat's also interesting to consider is how g changes as you burrow into the earth. The acceleration due to gravity becomes WEAKER as you descend toward the center of the earth, since you have matter BEHIND you trying to pull you back up with its gravity. Doing the math (it's actually a simple integral) shows that g decreases linearly with your depth. What that means is that, if you made your way to the center of the earth (and somehow weren't crushed by the pressure or burned by the molten iron), you'd be WEIGHTLESS!
W. Brian Lane
I am also quite shocked about the results, as dumb as I may sound I never knew that the surface of the planet doesn't always stay consistent depending on your location/position of where your at. I am also amused of how there are weak and strong "g's" on different places of earth's surface.
ReplyDeleteThis article is very interesting to me and quite shocking also. So does this explains why our weight on the moon is different from our weight of Earth? Since the gravity on the moon is (1/6) the gravity of the Earth. In previous science classes I was just told that you weigh less on the moon because the moon and the Earth are in different orbitals. None of my teachers really explained why.
ReplyDeleteThis is pretty neat. I just finished up some chemistry homework and was wondering how much gravity effects chemical reactions. Would a reaction differ it were on the moon. I am particularly interested in reaction rates.
ReplyDelete-Kyle Bosanko
That is amazing to think that I can possibly jump higher or weigh less depending where i am on the earth. I find what Dr. Lane said particularly interesting, I would have thought gravity increases as you go inside the Earth. But how far do you have to go into the Earth that the gravity decreases, where is the actual gravity maximum on Earth in terms of depth?
ReplyDelete-Steven DiGiannurio
Wow, this explains why we are so much lighter on the moon, I never knew the reason it was just how things were. Its cool that I now know that you weigh less on the moon because the gravity is only 1.7 m/s^2. Definitely gonna be showing my new knowledge off, haha. What kind of things will they be able to do with the gravity information from the moon?
ReplyDelete