# Why does rotation prevent the further contraction of the cloud?

In the book Horizons: Exploring the Universe (2018) by M.Seeds and D.Backman, chapter 9, page 170-171, it states that:

At least four factors resist the compression of an interstellar gas cloud, and those factors must be overcome by gravity before star formation can begin. [...]

Third, everything in the Universe rotates. As a gas cloud begins to contract, it spins more and more rapidly, just as ice-skaters spin faster as they pull in their arms. This rotation can become so rapid that it resists further contraction of the cloud.

Which bring the question of why does rotation prevent the further contraction of the cloud? Doesn't the rotation create a centripetal force that pointed inside, thus make the matters become denser, therefore it shouldn't be a reason that interstellar have to overcome in order to form stars?

• Gravity has to supply that centripetal force. Also see xkcd.com/123 ;) Apr 16, 2021 at 8:18
• @PM2Ring So the spinning created a centrifugal force, which is like Shot put, is that correct? And then I was wondering, why aren't we flying to the sky, due to the spinning of the earth? Is it due to gravity is greater? Apr 16, 2021 at 11:19
• Yes, the centripetal force required to keep an object spinning with the Earth is very small. Its maximum is at the equator, where it has a value around 0.3% of the gravitational force. en.wikipedia.org/wiki/Centrifugal_force is pretty good, but also see physics.stackexchange.com/q/109500/123208 Apr 16, 2021 at 13:50