Spinning the Physics
Plate spinning isn't neurosurgery. But it does require quick reflexes and a good sense of balance. It also helps to use the right plates. You won't be raiding grandma's china cabinet for these dishes. Most spinning plates have an indentation in the center that makes it easier for you to center the dowel as the plate rotates. They also have an upraised rim on the bottom that catches the dowel, particularly at the beginning of the trick. These plates are often made of heavyweight, unbreakable plastic, for obvious reasons.
To start the spinning, you hang the plate on this rim and begin rotating the stick. As the plate gains momentum and spins faster, it moves from a dangling, diagonal position to a horizontal one. At full speed, it doesn't wobble much at all, simply spinning in place.
It works because of gyroscope effects. Gyroscopes are essentially a type of spinning top, just like the children's toy you used to play with. Set a top in motion, of course, and it stands up on its pointy end until it runs out of momentum, after which it wobbles and then falls out of its spin and onto the floor.
Gyroscopes are self-balancing objects that are based on the principle of conservation of angular momentum, which is made up of both speed and direction. As an example, observe a spinning bicycle wheel. The speed of rotation is referred to as angular momentum. Most of the wheel's mass isn't in the center or the spokes; instead, it's distributed along the edges, in the tires.
Once that mass gets up to speed, its angular momentum tends to carry it along, providing stability that doesn't change much even when confronted with gravity. That's why you can carefully put a top (or other gyroscope) on a stand and orient it horizontally without it falling to the floor.
Plate spinning works much the same way. Apply force to the plate to make it spin, and its momentum holds it in place on the balancing stick without much work from you at all. The faster the spin, the greater the stability. Stability helps talented plate spinners perform dance moves, somersaults and other movements that add a wow factor to their acts without dropping the plates.
At its core, plate spinning isn't a complicated act. In fact, its simplicity is probably a big part of its appeal — you don't need fancy equipment or props to give it a try. Plate spinning's uncomplicated nature is also probably why it has persisted as a long-standing sideshow act and why it will continue to draw gape-mouthed stares for centuries to come.