> Of course, before you started, you made some measurements like how far the 
> car rolled straight given different starting heights. The strobe 
> lights/cameras helped too.

I remember we often made a "frictionless ramp", where we had to set the 
angle exactly to ensure a rolling ball stayed at constant speed.  Then we 
did some impact/energy/momentum stuff on the ramp.

I also remember in applied maths at school, working on the *theory* of 
friction and sliding/rolling balls etc, until someone piped up and pointed 
out that in theory this rolling ball would never stop on a flat surface :-) 
It wasn't until University that we solved that one with deformation of the 
surfaces and roughness. Actually that was one of my favourite courses, it is 
surprising how complicated the wheel/road interactions are, and that exactly 
the same theory of rubber tyres on tarmac applies to steel wheels on a steel 
track.

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