It's my understanding that any acceleration is caused by a force. When you remove that force it goes at a constant velocity. When an object is spinning it's accelerating, right? I mean the particles in the object are always changing direction. When left on it's own this leads me to beleive that eventually this should slow down. But that doesn't happen, it just keeps spinning at a constant speed. What force allows this system to keep accelerating. If my understanding of this is completely wrong please tell me otherwise.