Due to the conservation of which physical principle did the collapsing nebula flatten into a rotating disk instead of falling entirely into the center?

Answer

Angular momentum

As the cloud contracted, the conservation of angular momentum caused its rate of rotation to increase significantly, forcing the material, due to centrifugal forces, to flatten into a disk.

Due to the conservation of which physical principle did the collapsing nebula flatten into a rotating disk instead of falling entirely into the center?
Originstarplanetsolar systemhypothesis