All I know is that the wheel pushes the ground and the ground pushes back (friction). Pls can anyone elaborate on this process?


1 Answer 1


Let's say a vertical force $F$ acts on the wheel (e.g. the weight of a car or truck). The ground now provides a reaction force, known as the Normal force $F_N$:

Principle of fraction

Now if there acts on the wheel a traction force $F_T$ then in the simple case of static friction, a friction force $F_f$ arises, according to:

$$F_f=\mu F_N$$

where $\mu$ is the static friction coefficient between wheel and ground.

This causes a torque $\tau$ to arise about the wheel's centre of gravity $C$:

$$\tau=F_f R$$

with $R$ the radius of the wheel.

This torque causes angular acceleration $\dot{\omega}$ about $C$:


where $I$ is the inertial moment of the wheel.

So the wheel starts to turn about $C$, counter clockwise in this case.


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