bicycle, two-wheeled steerable machine that is pedaled by the rider's feet. On a standard bicycle the wheels are mounted in-line in a metal frame, with the front wheel held in a rotatable fork. The rider sits on a saddle and steers by leaning and turning handlebars that are attached to the fork.

A bike is a pedal-powered two-wheeled vehicle. If you don't have time to walk to work, you might decide to ride your bike instead. Bike is shorthand for a bicycle or a motorbike. A bike enthusiast might keep a bike rack on her car and a bike helmet in her trunk at all times.

The rider's muscular energy is converted to heat energy and the bicycle's kinetic energy while riding a bicycle. The rider's body is heated by heat energy. The bicycle is propelled in a circular motion by kinetic energy.

On a straight path, a bicycle has two forms of motion: rotational and rectilinear. The motion of an item around a circular route in a fixed orbit is known as rotational motion. Rectilinear motion is the movement of things along a straight line.