Question

The free surface of a liquid resting in an inertial frame is horizontal. Does the normal to the free surface pass through the centre of the earth? Think separately if the liquid is (a) at the equator (b) at a pole (c) somewhere else.

Answer 1

Explanation:

• Of course, the normal to the free surface passes through the centre of the earth.  
• Due to gravitational force of the earth, the free surface of the liquid takes the shape of surface of the earth.
• In addition, the normal to the free surface also passes through the centre of the earth as the direction of the gravitational force of the earth is towards centre of the earth.  
• The above scenario is applicable at the equator, at a pole and at somewhere else on the earth.