So the this one region of winds slows down the planet 1 millisecond a year, and not to mention us polluting, that heats the upper atmoshphere which does something to the winds and something yada yada yada and that slows it down too. Also, if a meteor were to hit Earth at a certain angle, it would slow/ speed it's rotation too! Read it during ISAT's today. Only for Illinois in US so :/ (Illinois Standard Achievements Test)