Re: What is the effect of different types of surfaces on the speed of a toy car

First, there are some basics about friction you need.  See, for instance,

   Laboratory:  Inclined Plane
   http://erebus.phys.cwru.edu/phys/labs/ip/theory.html

The above reference I found by searching the web for

   +friction +inclined_plane

[The '+' and '_' are important in this type search.]

And, here's a Java Applet simulation of friction on an inclined plane

   Inclined Plane Demonstration.
   http://www.nscl.msu.edu/~westfall/plane.html

Additional background information can be obtained from any high school or 
college physics textbook.  Some of these are probably available in your nearest 
library.

Without friction your car would slide down at its fastest speed.  It would 
slide because, without friction, there is no force to cause the wheels to 
turn.  If there is enough friction that the wheels will turn, and there is 
enough force to overcome the friction internal to your car (axles rubbing and 
that sort of thing), then your vehicle should travel down the incline at some 
characteristic speed.  Also, for a lighter toy car, surfaces with higher 
friction may have significant surface roughness, slowing your car down in much 
the same way a larger car would be slowed if traveling along a road with lots 
of potholes.  The later, where the variations in the surface are significant in 
comparison to the size of your wheels, is not the same as friction.

Thanks for your question.

sid