The discussion centers around the question of why gravity is perceived as strong in the North Atlantic Ocean, despite the thin crust typically associated with oceanic regions. Participants explore various factors influencing gravitational strength, including crust density, geological features, and the effects of Earth's rotation.
Participants express multiple competing views regarding the factors influencing gravitational strength in the North Atlantic Ocean, and the discussion remains unresolved with no clear consensus.
Limitations include the complexity of gravitational variations and the dependence on local geological features, which may not be fully accounted for in the discussion.
Not my favorite picture. A picture nominally is worth 1000 words, but not if it needs thousands of words to explain what is being depicted.meni ohana said:why gravity on Earth is very strong on the north atlantic ocean? ok, obviously where there is thick crust like himalaya (everest), huge land mass - more gravity, but the ocean?! where the crust is thin?!
source http://en.wikipedia.org/wiki/File:GRACE_globe_animation.gif
D H said:Not my favorite picture. A picture nominally is worth 1000 words, but not if it needs thousands of words to explain what is being depicted.
I'll start with a simple picture. Imagine a picture of the globe colored to indicate the gravitational acceleration, with 0 m/s2 being blue and 10 m/s2 being red. The whole globe will be almost the exact same color, red. If you look closely you'll see that the poles are a tiny bit redder than is the equator. Gravitational acceleration varies by latitude and altitude, from a low value of 9.764 m/s2 atop mountains near the equator to a high value of 9.8337 m/s2 at sea level at the North Pole.
Let's magnify this tiny difference (it's less than 1%) by subtracting 9.80665 m/s2 from the local gravitational acceleration. Now we're looking at a range of -0.04275 m/s2 to +0.02705 m/s2. It might help to multiply those small numbers by 100, yielding a range of -4.275 cm/s2 to 2.705 cm/s2.
Another name (deprecated) for cm/s2 is the galileo. We'll see that latitudinal variation in gravitation pop right out if we change our color scheme so that -4.3 gal is blue, +2.8 gal is red. The equator will be bluish, the poles reddish (and the North Pole will be considerably redder than the South Pole). You might see some slight variations in color locally, but it's not going to be strong.
The reason gravitation is strong at the poles than the equator is because the Earth is rotating. The rotation has a direct and indirect effect at the equator. The direct effect is that the rotation decreases gravitation. The indirect effect is the equatorial bulge that is a consequence of the rotation.
The next step is to remove these rotational effects as well. That's what this image is showing. The deep blue represents a deviation of -50 mgal (-50/1000 of a galileo, or -5×10-4 m/s2) from the local gravitational acceleration on featureless but spinning Earth while the red represents a deviation of +50 mgal. It's tiny, tiny, tiny.
That image does not show what you think it shows. That's why it's not my favorite image. It's neat if you know what it's showing, but it's not so neat when you have to explain the misconceptions that that image generates.
mfb said:In general, the crust thickness and density is different for different places - oceanic crusts tend to have a higher density (that's why they do not float up!).
You do see mountain ranges (as they just have mass where other parts of the surface do not), but you also see density differences below the sea level.
olivermsun said:
Just to add to this, NASA's publication Studying Earth's Gravity Field from Space says:
"The North Atlantic Mid-Atlantic ridge is an active spreading center where new crust is being created, and shows up as a strong positive anomaly in the middle of the Atlantic."