# Rolling motion terminology

Greetings,

I have a peculiar terminological issue. In a research paper I am writing, I need to distinguish between rolling wheels and rolling balls. The relevant difference for my purposes is that a wheel rotates around a single axis whereas a ball rotates around a single point. It's straightforward enough to refer to the locomotion of a wheel as " wheel locomotion" or more simply "wheeling," but "ball locomotion" seems awkward at best, and it goes, er, downhill from there!

It occurs to me that there may already be terms out there that are used to refer to and distinguish between "the rolling motion of a wheel" and "the rolling motion of a ball." I'm a biologist, and not a physicist, though, and I don't seem to know how to track down these terms, if they exist.

Any suggestions would be greatly appreciated!

It has been years since I took undergrad Classical Mechanics.

Can you go into more details about the purpose of the paper? What is it you need to "Distinguish".

Ill make some statements, you or anyone else can correct me, as needed.

Both the wheel and the ball have a single contact patch with the ground, depending on wheel and ball, the contact patch may be identical.

Wheel has an axle attached? Not just rolling downhill on it's own? Axle would limit degrees of freedom.

Ball is rolling downhill on it's own? Degree(s) of freedom pass through the center of the ball?

Without details on ball and wheel, moment of inertia cannot be calculated. I would think Moment of Inertia is critical to this discussion.

jmatejka,

Thanks for the reply. This particular paper is biological, not physical, in its focus; I'm describing an example of an animal that uses wheel locomotion, and I want to distinguish this type of locomotion, at a very basic level, from that of animals that roll, but in the shape of a ball, not a wheel. Wheels roll, and balls roll, but they don't do so in the same way, and I think this has some biological relevance.

Although I can see additional mathematical calculations in my future (i.e., finding moments of inertia, etc.), at this point I merely want to be able to refer to "wheel-type rolling" and "ball-type rolling" in an appropriate manner. I was hoping these types of locomotion might already have had different names.

Very interesting! I had not thought much of this locomotion for animals, I found some limited information here:

http://en.wikipedia.org/wiki/Terrestrial_locomotion

For ball type rolling, I would use "Sphere", for wheel type rolling I would use "Hoop or Cylinder". Here is a page with details on "Sphere" rolling, link at bottom has details on "Hoop" rolling:

http://hyperphysics.phy-astr.gsu.edu/hbase/sphinc.html

Ill again make some general relevant comments for you or anyone else to question or critique:

Rolling seems to be used by animals primary as an escape mechanism.

Most rolling "animals", ball or otherwise, use gravity,but some is powered.

The Sphere would seem to be more "rapid change in direction" friendly.

Whether "Sphere" or "Hoop", smaller initial diameter would aid the initially rolling,(smaller moment of inertia).

I'm guessing the animal/nature "chooses" "Hoop" or "Sphere" based on what works best for thier mass/anatomy. Nature is very good at figuring out what works best for a particular application.

Hopefully this has been somewhat helpful and others will chime in.