2 Surface GravityWe 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 mEarth’s mass: 5.97 x 1024 kgCalculate: 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, tooThe material under the surface is not uniformThe earth is spinningThe tides affect the earth as well as the oceansThe unit of gravitational acceleration used on the Earth is the Galileo.1 Gal = 1 cm/s2g = 981 Gal
4 Effect of HeightHigh 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 RotationThe earth is made of layers of different types of rock.These rocks can move due to daily tides.Much less than ocean tidesPeriod is 12 hours like the oceanColorado 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: m/s2North Pole: m/s2Colorado 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 = w2rnext