Eli5 on why do planets spin?
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Really big objects like planets are squishy when they collide with other planet size objects.
If two planets of the same size going the same speed hit head on, they would stop moving. This is because “forces” cancel out.
If these two objects hit off center, up/down/left/right, some of their energy becomes “spin” energy. If you’ve ever pushed on the side of a swivel chair you have seen this.
If one of the planets has more “momentum” because it is heavier or faster or some combination, the new “clump planet” will move in the direction of the planet with more momentum, just slower.
If the planets hit at an angle, like if one object was going north east and another north west, they would then move north, depending on which was faster/heavier.
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