Question

The blades of a fan rotate more and more slowly after the fan is shut off. Eventually they stop rotating altogether. In such a situation, we sometimes assume that the angular acceleration of the blades is constant and apply the equations of rotational kinematics as an approximation. Explain why the angular acceleration can never really be constant in this kind of situation.

Answer 1

it can be seen that fan rotates even after switching it off , is because of moment of inertia . But at every instance frictional forces it can be air or mechanical friction inside fan caused by the bearings , so eventually it comes to rest .

In this process the angular velocity (angle covered per unit time keeps changing continuosly ) i.e, angular velocity is not a constant . So the angular accerlation which is described as the change in the in the angular velocity per unit time also changes obviosly . So the angular accerlation can not be constant .