Question: A student said, "When the Moon goes around the Earth, there is an inward force due to the Moon and an outward force due to centrifugal force, so the net force on the Moon is zero." Give two or more physics reasons why this is wrong.

In a circular motion, the centrifugal force works along the circle's radius and acts away from the circle's centre.

When measuring in an inertial frame of reference, the force does not exist. It only becomes relevant when switching from a ground/inertial to a spinning reference frame.

The net force on an object can be expressed as the sum of two parts and it is equal to the rate of change of the momentum.

The two parts that we are taken about are the parallel rate of change of the momentum and the perpendicular rate of change of the momentum .

Write the net force on the object.

The moon experiences an inward gravitational attraction as it revolves around the Earth. Although there is an outward centrifugal force, it is not a true force. On equating them, the result will be a non-zero net force on the moon. As a result, the stated assertion is incorrect.

The object is moving in a curved path, and its momentum is constantly changing. Even if the object moves with constant speed, a change of direction indicates that $\frac{d^{\omega }p}{dt}$is non zero.

Hence, the net force is non zero.