Shape, dimensions, physical
basis of the Earth
2nd lecture of the course “Introduction to Geology”
1. Form
Its actual shape is expressed by the so-called "geoid" - a physical surface perpendicular to
the vector (direction) of the force of gravity. In the oceans it coincides with the water
surface, while on land it is an extension connecting water basins.
2. Size
Size controls how much heat (internal energy) is given off. The approximate radius of the
Earth is 63,788 m.
3. Density
The average density of the Earth is calculated in gals and is 5.517 g/cm3. It is a
combination of the densities of three types of material, also derived from a comparison
with the known densities of rocks. The materials are: water with density = 1, silicate
material with density = 3g/cm3 and iron-nickel alloy with density = 8g/cm3. The average
density of the Earth is a mixture of ⅔ silicate material from the Earth's crust and ⅓
iron-nickel alloy from the core. It is unevenly distributed and is controlled by a number
of parameters.
4. Gravity
This is the force with which the Earth attracts bodies, it is the result of gravity and
centrifugal forces and depends on the mass, shape and size of each individual point.
Gravity between two objects varies according to their mass and the distance between
them. The gravitational coefficient is directly proportional to the mass and inversely
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basis of the Earth
2nd lecture of the course “Introduction to Geology”
1. Form
Its actual shape is expressed by the so-called "geoid" - a physical surface perpendicular to
the vector (direction) of the force of gravity. In the oceans it coincides with the water
surface, while on land it is an extension connecting water basins.
2. Size
Size controls how much heat (internal energy) is given off. The approximate radius of the
Earth is 63,788 m.
3. Density
The average density of the Earth is calculated in gals and is 5.517 g/cm3. It is a
combination of the densities of three types of material, also derived from a comparison
with the known densities of rocks. The materials are: water with density = 1, silicate
material with density = 3g/cm3 and iron-nickel alloy with density = 8g/cm3. The average
density of the Earth is a mixture of ⅔ silicate material from the Earth's crust and ⅓
iron-nickel alloy from the core. It is unevenly distributed and is controlled by a number
of parameters.
4. Gravity
This is the force with which the Earth attracts bodies, it is the result of gravity and
centrifugal forces and depends on the mass, shape and size of each individual point.
Gravity between two objects varies according to their mass and the distance between
them. The gravitational coefficient is directly proportional to the mass and inversely
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