geophysic lec 5 Gravity

first to speculate that the Earth was a sphere

• 275-195 BC: Erastosthenes

• 582-507 BC: Pythagoras

• 1671: Jean Picard

first scientifically sound estimate of the size of the Earth (circumference) - Used and studied the approximate diatsnce of the cities Alexandria and Syene. - his estimate of the Earth’s circumference is equivalent to 46,250 km, about 15% higher than the modern value of 40,030 km.

• 275-195 BC: Erastosthenes

• 582-507 BC: Pythagoras

• 1671: Jean Picard

A French astronomer - completed an accurate survey by triangulation of the length of a degree of meridian arc. - From his results the Earth’s radius was calculated to be 6372 km, remarkably close to the modern value of 6371 km.

• 275-195 BC: Erastosthenes

• 582-507 BC: Pythagoras

• 1671: Jean Picard

Polar diameter

equatorial diameter

Earth’s reference surface

Over the oceans, the geoid is the

Causative body: a rock unit of different _ from its surroundings

• density

• composition

• specific gravity

• type

Directly measures small differences in the strength of gravity

- variations in the weight of the mass caused by variations in gravity cause the length of the spring to vary. The spring has a dual function of supporting the mass and acting as the measuring device

• Stable Type (Static) Gravimeters

• Modern/ Unstable (Astatic) Gravimeters