That's a sphere.
A curved surface on which all points are the same distance from the center is called a sphere.
That's a circle. The "fixed point" is the center of the circle, and the constant distance is its radius.
Motion directly either toward or away from the center is 'radial' motion. Motion where the distance from the center is constant is 'tangential' motion.
A sphere.
Downward motion is defined as the movement of one's center of gravity towards the performance surface.
The distance from surface to surface through the center of a planet would be that planet's "diameter".
The average distance from Earth's surface at the equator its center is about 6378 km. The distance from near the north and south poles to the center is somewhat less.
A curved surface on which all points are the same distance from the center is called a sphere.
7,000 km
It is the average distance between the centres of the two objects.
That's a circle. The "fixed point" is the center of the circle, and the constant distance is its radius.
focal length..
focal length..
Crust, mantle, core
The earth is an regular surface in average with a great number of small irregularities (small with respect to the global earth surface). The geometrical center of earth is obtained by approximating the earth surface with the best fitting rotational ellipsoid, with a circular section corresponding to the equator and a minor axis joining the geographical poles. The so called "sea level" is defined as the average distance from the geometrical center of earth of all the points on the sea surface. The altitude of a single earth point is the difference between the distance from the earth center of that point and the conventional sea level.
It's the part that is the same distance from all points on the surface.
A sphere.