The object of ball bearings and roller bearings is the substitution of pure rolling motion for plain sliding friction. Ball Bearings rely on the rolling motion of hardened steel balls to absorb loads. This rolling motion produces far less friction than the sliding motion. These steel balls are held in circular rows between an outer and inner ring, which have raceways, or slots, grooved into them to guide the balls. Ball bearings are available in both filling-slot and no filling-slot types. Other types of bearings have developed from these basic designs, like double-row and deep groove bearings, to handle specific...
accommodate thrust in either direction.

Duplex bearing. - Used to take heavy thrust in either direction or some radial load.

Adaptation sleeve bearing. - This bearing is mounted on a tapered split sleeve to simplify assembly on long shafts.

No matter what type of ball bearing system they all have one common function, to turn sliding forces into rotational forces, so that the coefficient of friction is reduced and hence so is the force opposing the motion friction. There is some friction but this is much lower than if two surfaces where slid over the top of each other.