At first thought, you may think that the human rider is what keeps a bicycle balanced. This ends up not being completely true. If launched properly, a modern bike with no rider balances itself just fine and continues on its path as if a rider were guiding it. This can be easily verified by anyone with a bike, and can make for amusing scenarios such as in this video (http://www.youtube.com/watch?v=9ewqeheLL_I) . Up until a few decades ago, scientists thought a bicycle is self-balancing when in motion because of gyroscopic effects and caster effects alone. "Gyroscopic effect" means that a spinning wheel tends to stay aligned in its original direction. This effect is used in mechanical navigation gyroscopes to maintain a proper sense of direction as a vehicle travels about. The gyroscopic effect is a direct result of the conservation of angular momentum, or spinning motion. In the absence of an external force, the total angular momentum of a system must retain the same strength and orientation. As a result, a small force does little to make a fast-spinning heavy wheel tilt away from its original orientation