Wheel Confusion

[DonRotolo]

Sure.

Inline means straight ahead. A bicycle wheel usually rolls inline and not traverse.
Traverse is sideways. If you grabbed a bicycle by the wheels and dragged it, that's traverse.

Static means not moving relative to the ground. On a bicycle, unless the wheels are skidding, that's static friction. Note that this doesn't mean the wheel is not moving, just that it is not slipping against the ground.
Dynamic means it is slipping.

So, a wheel happily rolling down the field with no slip sees 0.06. One skidding down the field sees 0.05.

What does 0.06 mean? 0.00 means there is no friction at all, 1.00 means they are solidly locked (maybe glued together?). Anything in between is how much they can slip, or more accurately how easily they can slip against each other. This Coefficient of Friction is denoted by the greek letter Mu.

A rubber tire against dry pavement has a Mu of maybe 0.8 or 0.9
That same tire has a Mu of about 0.1 or 0.2 on smooth ice.
A spiked golf shoe has a mu close to 1.00 on carpet.

Does that help?

[Brown 2010]

yes. very much. thanks.


so if im understanding this right, than if the wheel is static, and sideways(transverse) than it has twice the grip? than if it was inline? is that right?

[DonRotolo]

Yep, that's right.

[Matt H.]

What does 0.06 mean? 0.00 means there is no friction at all, 1.00 means they are solidly locked (maybe glued together?). Anything in between is how much they can slip, or more accurately how easily they can slip against each other. This Coefficient of Friction is denoted by the greek letter Mu.

A rubber tire against dry pavement has a Mu of maybe 0.8 or 0.9
That same tire has a Mu of about 0.1 or 0.2 on smooth ice.
A spiked golf shoe has a mu close to 1.00 on carpet.

Does that help?

Don,
That's really not a correct description of friction. A Mu of 1.00 does not mean two surfaces are solidly locked together. There is no limitation that mu must be between 0-1. In fact many object pairs have a mu greater than 1.00. Mu is a dimensionless constant found by comparing the downward force on an object to the force resisting its motion. For example in you have a 120 lb robot a mu of .05 means only the wheels can exert 6 lbs of forward force using friction before they being to slip. If the wheels have a mu of 1.5 then the robot can exert 180 of pounds of force using a frictional connection to the ground before slipping.

A real world example of a mu higher than one would be copper on copper 1.3 silver on silver 1.5 etc. source: http://www.engineershandbook.com/Tab...efficients.htm

[ChuckDickerson]

And as a point of reference the old roughtop/wedgetop tread used by many teams prior to being made instantly obsolete yesterday has a CoF around 1.2-1.3 on the old playing carpet. Alas, it is a whole new era...

[spc295]

how is this supposed to simulate traction on the moon? .05 is like 1/20 what we had not 1/6?

[BigWhiteYeti]

The surface of the moon is dusty, from what I hear. The gravity is 1/6, which would generally make the friction 1/6. The only question is what is your baseline for friction on a dusty surface on Earth.

I don't think they really are aiming for literal accuracy here, the moon theme is just that, a theme.