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Gravity Near Earth

Gravity Near Earth. Surface Gravity. We think of gravitational acceleration as g = 9.8 m/s 2 . This value is due to the universal gravitational force. Earth’s radius: 6.37 x 10 6 m Earth’s mass: 5.97 x 10 24 kg Calculate: g = F / m = GM / r 2 = 9.81 m/s 2 . Variations.

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Gravity Near Earth

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  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 Colorado School of Mines

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

  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 next

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