Where in North America is the value of acceleration due to gravity the greatest and where is it the least?

Question

I have searched and can't find the answer. I can get extra credit for this and time is running out!

Answer 1

A naive guess would be that Death Valley would have the most and mount McKinley would have the least just because of altitude. Actual gravity may depend on other factors as well, but that's a decent guess anyway.

Answer 2

My guess is that the effect of the earth's radius outweighs that of altitude. Per the ref., the radius at the equator is 22 km greater than at the poles*. Thus, primarily, the closer to the equator you are the less the gravity. Also, addition of the centripetal acceleration of Earth's rotation reduces the net g, especially at the equator since that effect increases with radius. I would look for the highest altitude point in Panama for the lowest value of gravitational-only g (and net g) in North America, and the lowest altitude point in northernmost Canada for the highest. At the poles, the gravitational-only and net g are the same (since there is no centripetal acceleration there), 9.8640 m/s^2. At the equator, the gravitational-only g is 9.7982 m/s^2 and the net g is 9.7645 m/s^2. An equatorial Mt. McKinley would reduce those numbers by about 0.02 m/s^2 making a very low-g point. But its actual location nearer the north pole works against its altitude and results in a mid-range value of g.
*But note that a simple radius value doesn't tell the whole story on g. It would if the Earth were a sphere (and of uniform density), but for an ellipsoid the simple inverse-square relationship of g to radius is not exact.

Answer 3

Death Valley, Ca and Mt. McKinley , AK