A cart is a simple, wheeled mechanical device designed primarily for the transport of loads over land. It consists of a chassis or bed upon which goods are placed, and is typically supported by one or more axles, which connect to wheels. The structural design must account for the type of load, the intended terrain, and the method of propulsion. Historically, carts evolved from basic sledges and dragged wagons, constantly improving efficiency through changes in wheel materials, axle placement, and coupling mechanisms. Mechanically, the basic principles involve applying force to move the entire system, utilizing the rolling resistance offered by the wheels to minimize energy expenditure during transport.