Question

Is the radius of the Earth the same everywhere?

Answer 1

Hint: The shape of Earth is changing very slowly and is not a perfect sphere. Earth’s rotation, wobbly motion and other forces have caused the North and South Pole to slightly flatten. Due to the bulging caused by the earth’s spinning, it is often called an ‘ellipsoid’.

Complete answer:
No, the radius of the earth is not the same everywhere. Earth is an imperfect sphere with slightly flattened poles and is called an ellipsoid. An inertial tendency called the centrifugal force causes objects to move in a circular motion away from their centre. This force when exerted by the rotation of the earth on its axis causes it to bulge out at the equator which, in turn, brings about the variation in the radius from place to place much like how spinning pizza dough in the air causes it to flatten.

The slow but constant shift in the shape of the earth leads to a change in distance between the centre of the earth and its crust. Since the radius is calculated as the distance between the core and a point on the surface of the earth, it increases as we move towards the equator from the poles. The radius of Earth at the poles (polar radius) is 3,950 miles/6,356 km and rises to 3,963 miles/6,378 km at the equator. This difference of 13 miles/22 km symbolizes the irregular shape of the Earth called the GEOID.

Note: The average change in Earth’s radius is estimated to be 0.004 inches (0.1 mm) − about the thickness of a human hair− per year and is considered statistically insignificant. Earth’s mean radius is the average distance between the physical centre and the surface and its SI unit is $6.3781×10^{6}$ m.