Discounting the air resistance, why if one pushes a wheel on a flat terrain it eventually stops?

Question

Newton's third law states that a body in movement will keep moving if no forces stop it. If the wheel rotates without sliding, what forces are there to stop it? I'm asking because i try to understand what forces a car must overcome other than air friction to just keep moving.

Any personal answers, equations or links to websites are appreciated, thanks.

Answer 1

Think of the wheel as sticky. All materials stick to each other to some degree (molecular welds). The back of the wheel will have to peel off the ground which takes energy. I am sure you can picture a sticky wheel.

Answer 2

Well you're right that air friction would be one way to stop the car...however, unless the wind was blowing really hard, it would take a while to stop vehicle.  The biggest force that acts upon the car is friction with the terrain.  Even if the terrain is flat, the car is still having to overcome friction in order to move.  This friction from the ground, in accordance to the friction in the air, stops the car from moving.

Answer 3

A rubber tire is not an exact circle on the road.  The rubber deforms to have the small flat area in contact with the road.  The tire is constantly flexing and unflexing as the tire rotates and the car moves along.

There is also bearing friction and moving the oil and grease in those bearings.  There are gear losses in the differential.  There are transmission losses and finally motor losses - which are considerable.  

Answer 4

An automobile tire, because it is soft, has a lot of friction with the ground. Because it is soft, you can look at it as always climbing a small hill.

By contrast, a train wheel on a steel track has very low friction. A car on level rails will coast for miles before it stops.

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Answer 5

Well, there will be friction with the wheel rolling on the ground.  Any CONTACT with the ground will cause friction if the wheel rotates, while touching the ground.   The contact with the wheel to the ground causes heat or friction. Friction will rob the rotational energy from the wheel, causing the wheel to stop eventually, unless you provide more energy to overcome the friction.    

Answer 6

Another element is friction with the terrain itself, due to gravity pulling the wheel against the terrain.  Another factor would be the weight of any object attached to the wheel.