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An old question?



I think that it is OK to ask a question which was already
discussed if one has trouble with an issue connected
with teaching. In preparing for tomorrow's lecture I am
again having a difficulty with explaining the mechanism
by which the centripetal force starts acting on the car
(on its wheels) when the steering wheel is turned.

I draw two pictures. On the first picture the planes of all
four wheels are parallel, in the second the planes of the
front wheels are at an angle, for example, 20 degrees,
with respect to the planes of the back wheels. The back
wheels are still oriented as they were when the car was
moving forward along the straight line. The front wheels,
however, are now oriented to make sure the car is turning
to the left.

I am supposed to say that the centripetal force is provided
by the road; it is a familiar static friction force. But this is
not enough; something essential is missing to make this
acceptable. Am I the only one who is bothered by this?

The sidewise force would not appear (ideally), if all four
wheels were suddenly locked, no matter what their
orientations are. I am thinking about a situation in which
wheels are locked when the car is in the air, for example,
when going too quickly over the top of a hill. The sidewise
force (to the left on my picture) appears only when wheels
are rolling. Therefore, rotation of wheels should be an
essential element of my explanation. But I am not able
to generate such explanation. Please help.
Ludwik Kowalski