1. Gravity Near Earth

2. Surface Gravity
We think of gravitational acceleration as g = 9.8 m/s2.
This value is due to the universal gravitational force.
Earth’s radius: 6.37 x 106 m
Earth’s mass: 5.97 x 1024 kg
Calculate: g = F/m = GM/r2 = 9.81 m/s2.

3. Variations Gravity varies over the surface of the Earth.
The height of the surface varies – so the radius does, too
The material under the surface is not uniform
The earth is spinning
The tides affect the earth as well as the oceans
The unit of gravitational acceleration used on the Earth is the Galileo.
1 Gal = 1 cm/s2
g = 981 Gal

4. Effect of Height
High areas have a greater distance from the center of the Earth.
An increase of 1 km should decrease g by 300 mGal.
USGS

5. Earth’s Rotation
The earth is made of layers of different types of rock.
These rocks can move due to daily tides.
Much less than ocean tides
Period is 12 hours like the ocean
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6. Latitude Changes As the Earth spins the equator slightly bulges.
The radius is about 22 km bigger compared to the pole.
Expect a few Gal difference from equator to pole.
Equator: m/s2
North Pole: m/s2
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7. Centripetal Correction
The spin of the earth creates a centripetal acceleration toward the axis of the earth.
The effect is like accelerating down in an elevator.
Items weigh less at the equator.
a = w2r
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