Today, poorly drawn Calvin’s dad will teach you about constant angular velocity and constant linear velocity. This depends on the kind of spinny music in question.

Vinyl records have constant angular velocity. They spin at the same number of revolutions per minute regardless of where the needle is. This means the surface passes under the needle faster at the edges than in the middle, because the outer edge of the disk is longer than the inner edge, but an entire revolution goes by in the same amount of time. “Surely,” you say, “This must mean that the record technically has higher fidelity at the edges than at the center?” This is absolutely correct.

CDs have constant linear velocity. The surface must pass by the laser at the same rate all the time, because the interval of the ones and zeroes (it’s slightly more complicated than that, yes, quiet in the back there) must remain the same. Unbeknownst to you unless you’re a hyper nerd, your CD player speeds up and slows down its spindle depending where on the disk it’s reading.