Simplify the following text for a Grade 9 native English-speaking person.
Original: Sylvia is also a fairly fast rotator , turning about its axis every 5.18 hours ( giving an equatorial rotation velocity of about 230 km\/h or 145 mph ) .
Simplified: Sylvia is also a fairly fast rotator , turning about its axis every 5.18 hours ( giving an equatorial rotation speed of about 230 km\/h or 145 mph ) .