Once a wheel is spinning in a plane ( that means in a flat surface, like a table in space), it does not want to change it's It wants to keep spinning in the same plane. The spinning is called rotation. The word inertia can be found in our GLOSSARY page. The rotation inertia is like the spinning energy. It is what makes the spinning thing want to keep spinning in the plane it is on. GYROSCOPIC STABILITY has to do with MASS and INERTIA. Once mass is set in motion, it continues on that line until some other force acts on it. Have you ever played with a gyroscope? It will spin and spin in one plane unless it bumps into something or it gets pushed. The push or bump is another force. In a yo-yo, for example, the yo-yo spins around an AXIS . Its axis is the middle axle that holds the two sides together. It will rotate HORIZONTALLY, VERTICALLY or DIAGONALLY. When you do a yo-yo trick you usually put a force on the yo-yo and make it change its plane of rotation. In aeronnautics and nautical engineering, gyroscopic stability is used in navigation and other parts of boats and planes. For more information on that, go to PRACTICAL USES. A Challenging Question: 1. How come a boomerang comes back when you throw it For the ANSWER 2. Why do you throw a boomerang vertically instead of horizontally like a frisbee? For the ANSWER