Gravity Near Earth

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.

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

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

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 Colorado School of Mines

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: 9.780 m/s2 North Pole: 9.832 m/s2 Colorado School of Mines

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 next