Editing Wheel (section)

==Mechanics and function==
{{About|the application to transport|the simple machine|Wheel and axle|section=yes}}

A wheeled vehicle requires much less work to move than simply dragging the same weight. The low resistance to motion is explained by the fact that the [[friction|frictional work]] done is no longer at the surface that the vehicle is traversing, but in the [[bearing (mechanical)|bearings]]. In the simplest and oldest case the bearing is just a round hole through which the axle passes (a "[[plain bearing]]").  Even with a plain bearing, the frictional work is greatly reduced because:
* The normal force at the sliding interface is same as with simple dragging.
* The sliding distance is reduced for a given distance of travel.
* The coefficient of friction at the interface is usually lower.

Example:
* If a 100&nbsp;kg object is dragged for 10 m along a surface with the [[coefficient of friction]] ''μ''&nbsp;= 0.5, the [[normal force]] is 981 [[Newton (unit)|N]] and the [[Mechanical work|work]] done (required [[energy]]) is (work=force x distance) 981 × 0.5 × 10&nbsp;= 4905 [[joule]]s.
* Now give the object 4 wheels. The normal force between the 4 wheels and axles is the same (in total) 981 N. Assume, for wood, ''μ''&nbsp;= 0.25, and say the wheel [[diameter]] is 1000&nbsp;mm and axle diameter is 50&nbsp;mm. So while the object still moves 10 m the sliding frictional surfaces only slide over each other a distance of 0.5 m. The work done is 981 × 0.25 × 0.5&nbsp;= 123 joules; the work done has reduced to 1/40 of that of dragging.

Additional energy is lost from the wheel-to-road interface. This is termed [[rolling resistance]] which is predominantly a deformation loss. It depends on the nature of the ground, of the material of the wheel, its inflation in the case of a tire, the net torque exerted by the eventual engine, and many other factors.

A wheel can also offer advantages in traversing irregular surfaces if the wheel radius is sufficiently large compared to the irregularities.

The wheel alone is not a machine, but when attached to an [[axle]] in conjunction with bearing, it forms the [[wheel and axle]], one of the [[simple machine]]s. A driven wheel is an example of a wheel and axle. Wheels pre-date driven wheels by about 6000 years, themselves an evolution of using round logs as rollers to move a heavy load—a practice going back in pre-history so far that it has not been dated.