Final answer:
A cloud collapses rapidly at first due to the stronger gravitational force in higher density regions, but as it becomes denser, the collapse slows down due to increased pressure and the conservation of angular momentum leading to disk formation.
Step-by-step explanation:
A cloud collapses rapidly at first due to the inward pull of gravity in regions of higher density. These denser regions exert a slightly larger average gravitational force, causing them to acquire more mass and thus collapse. As they collapse, they initially do so quickly, representing a rapid increase in density.
However, as the cloud becomes denser and the density increases to a critical level, the gravitational collapse slows down. This slowing down is partly because, as the material falls in, it heats up and generates pressure that opposes the force of gravity. Additionally, conservation of angular momentum causes the collapsing cloud to spin faster, leading to the formation of a disk-shaped structure, where the spin rate is slower near the poles and faster near the equator. This disk formation further moderates the collapse, especially in the regions farther from the center.
The collapse continues until equilibrium is reached or until new physical processes, like nuclear fusion in the case of star formation, halt the collapse. The sequence of events leading from a diffuse cloud to a dense object like a star or even a neutron star shows how the initial conditions and the conservation laws like that of angular momentum play fundamental roles in the development of cosmic structures.