A partially dismantled bicycle.
Human-powered machines have been in use for thousands of years, and the bicycle is one of the most prominent of such machines, which still sees use today. Bicycles consist of two wheels, one behind the other, attached to a frame. A human rider sits atop the frame, and has access to the pedals, handlebars, and the brakes. To move the vehicle forward, the rider moves the pedals with their feet in a circular motion. A chain transfers energy to the two wheels, moving the bike forward. To stop, most bikes have brake levers on the handlebars which are depressed by the rider.
Sold in bicycle shops and department stores, and used by people of all ages.