Eli5 on why do planets spin?
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Here’s another way to think about the question.
If you have a planet going around the Sun, and it didn’t “spin” at all (fixed orientation with regard to the galaxy), it would be rotating from the point of view of the Sun, wouldn’t it?
And a planet going around the Sun, always facing the Sun with the same face (not “spinning” relative to the Sun) would be spinning in relation to other objects in the solar system / galaxy.
So spin one way or another is going to happen. But perhaps you mean, why do planets spin so quickly relative to their orbit around the Sun? That’s answered by others well enough — when matter condenses together, it has a tendency to have some angular momentum to it. Just as planets orbit the Sun, so does matter “orbit” or spin when formed into a planet.
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