Wheels are added to trolleys to reduce friction. As rolling friction is lesser than sliding friction, adding wheels to trolleys reduces opposition to motion.

Luggage is provided with wheels to solve the "last mile" problem of modern travel: the physically taxing task of transporting heavy personal belongings through sprawling airports and train stations. Interestingly, the wheeled suitcase was only "officially" invented in 1970 by Bernard Sadow, who observed a worker moving a heavy machine on a wheeled pallet. Before this, travelers relied on porters or their own physical strength to carry trunks and suitcases by hand. The invention took nearly 5,000 years because of gendered social norms; the travel industry long assumed that men would find rolling a bag "unmanly" and that women would always have a man to carry their bags for them. In 1987, pilot Robert Plath revolutionized the design with the "Rollaboard," which featured two wheels and a telescoping handle, allowing the bag to be pulled upright. Today, wheels are a standard necessity because they dramatically reduce the risk of back and shoulder injuries, making global travel accessible to people of all physical strengths and ages.