[GeoffP]

excellent setup and experiment thanks for the info. I'll stick my neck out on this one. dynamic friction is dynamic friction. unless you have something to provide traction in one direction vs another then it should be the same in all directions because it is an intermolecular bond. in-line scratches from wear may develop which could provide some difference between the in-line and transverse but i doubt a 2-fold increase with 120lbs and this soft of a material. Do your test results suggest they meant static vs dynamic friction? I would expect a 2:1 ratio there. did you happen to measure the force required to initially move the cart from rest and then the force required to keep the cart moving at a constant velocity? I would be very interested in that. we are thinking of limiting our acceleration so we don't exceed the static frictional forces.
thanks again and great job setting that up.