Schijnbaar gewicht en de rotatie van de Aarde

Consider an object of mass m suspended from a spring scale attached to a rigid support at the Earth's equator. The scale reading is the object's apparent weight mg', equal to the magnitude of tension force F_t in the spring.

If the Earth was a non-rotating body, the tension force would be equal to the gravitational force F_g acting on the object, keeping it in equilibrium.

Recall that the magnitude of the gravitational force is the true weight mg of the object.

However, since the Earth rotates about an axis passing through its poles, the object at the equator describes a circle around the Earth's rotational axis. Therefore, it has a centripetal acceleration directed towards the Earth's center.

Hence, the forces acting on the object are the gravitational force directed towards the Earth's center, the tension force in the spring directed away from the Earth's center, and the centripetal force directed towards the axis of rotation.

Therefore, the apparent weight equals the true weight minus the centripetal force. At the poles, the centripetal force on the object is zero, implying that mg' equals mg.