system
Given the following post, respond as if you're commenting on Reddit:
human
Solar System Formation

Why is it that when solar systems form, the mass doesn't just all come together to form one giant ball? In other words, where does the velocity come from to keep the planets from just falling into the sun during formation?
gpt
Imagine a very large, elongated cloud of hydrogen in space. It's slowly falling in on itself due to gravity, but it has no angular momentum, so everything is falling toward the center. 

There's a star nearby. Because of the elongation of the cloud, one end of it is nearer to the star than the other end, but it's at some angle to a line from the center of the cloud to the center of the star. The star goes supernova, its shockwave hits the near end of the cloud, which begins to move away from the star. This shockwave hits the other end too, but it's more distant, so the force is less by some 1/r factor.

Since the cloud was already falling in on itself, when you add the falling in velocity to the differential shockwave velocities across the cloud, you get a net rotation of the cloud.

This is just one example, there are probably other ways for there to be an initial rotation.