Physics (10th Edition)

Published by Wiley
ISBN 10: 1118486897
ISBN 13: 978-1-11848-689-4

Chapter 9 - Rotational Dynamics - Check Your Understanding - Page 241: 19


The angular velocity of the star is greater than that of the cloud.

Work Step by Step

According to the conservation of angular momentum, $$ I_0\omega_0=I_f\omega_f$$ When the gas particles are pulled together, the distance $R$ of the cloud's mass from the axis of rotation decreases till the point the cloud becomes a star. And because $I=\sum MR^2$, the star's moment of inertia is less than the former cloud's moment of inertia. Because angular momentum is conserved before and after the action, since $I_{star}\lt I_{cloud}$, $\omega_{star}\gt\omega_{cloud}$.
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