A bicycle is a human-powered or motor-assisted, pedal-driven two-wheeled vehicle with a frame, one wheel in front of the other. The name “bicycle” derives from the French words for ‘hobby horse’ and’velocipede’, meaning two-wheeled vehicle. Bicycles are typically equipped with handlebars for steering, and a seat for the rider to sit in. They can be fitted with a hitch to carry cargo or a child seat, and can be customized with a variety of accessories for racing, touring, casual riding, or everyday transportation.
It may seem surprising, but the bicycle is an incredible feat of physics. We still don’t really understand how it works. Physicists have developed theories, but no complete explanation is known. The most popular theory is that the gyroscopic forces created by spinning wheels hold the bicycle upright. You can test this theory by removing a wheel from your bike and, while it is spinning, crook your finger under one of the spokes. The wheel resists this force, as if invisible hands are holding it up.
Another important theory is that the bicycle’s tires generate forces that push it forward. You can also test this by removing a tire and, while it is spinning, trying to twist the axle. The tire resists this, again as if invisible hands are holding it up. These elliptical regions under the tires, called contact patches, are the only places where the bicycle interacts with the road and almost all of the rider-controlled forces that control acceleration and braking act through these areas.
The classic design of the bicycle is a triangle consisting of frame tubes with lugs at the corners for attaching the wheels and cranks. Modern bicycles often incorporate more complex geometries and materials for weight, strength, and versatility. The use of alloy steels, for example, has made it possible to create frames that are lighter and stronger than ever before. Modern composite materials such as carbon fiber are also used for frames and components, but require special care to ensure that the stresses produced by pedaling are properly distributed.
The shape and geometry of the bicycle’s frame is a critical factor in its performance. For maximum efficiency, a bicycle should be designed with its center of gravity over the wheel’s axle. This will keep the pedals from hitting the ground on steep turns and make it easier to steer. It is also a good idea to shift gears before you start climbing hills so that the chain isn’t in the wrong place on the cassette or cogs and that your transmission is working as effectively as possible. It’s best to avoid shifting while you are pedaling, since doing so can cause the chain to fall off of the cassette or rear cogs and leave you stranded.