Meet the Researchers:
Something you do because you want to
Interview with Ryan O'Donnell
Ryan O'Donnell '03 recently received an Anton Fellowship to study the behavior of frictional forces in granular matter with physics professor Arshad Kudrolli. Ryan discussed his research in a recent interview.
Ryan, how did you get involved in research at Clark?
Freshman year, Arshad Kudrolli was my intro physics teacher. He was really proactive about encouraging any students interested in doing hands on physics in his lab. He took the entire class through his lab twice during the year, just to show us what it was all about and what he was interested in. He said that if any of us were interested in participating in his research group to come and see him. Sophomore year I didn't have him as a professor, but I kept in touch and we decided by the end of that spring that I was going to spend time in his lab over the summer. So that's what I did. He found a project within what he was doing and put me at the reins. From there it's taken off. I spent the summer between my sophomore and junior years, a decent part of my junior year, and this previous summer in his lab.
How did you hear about the Anton Fellowship program?
Arshad mentioned that it might be a good idea to apply to it so I could get funding for the research I was doing. I decided it would be worth a shot.
Was the first project you worked on in his lab also on granular matter?
Yes, I've been working on pretty much the same project the entire time. It has to do specifically with frictional forces in granular matter. Basically, what I'm doing is sliding carts [see animation] over the surface of a "sand" bed and looking at the different forces that come from the motion of the cart.
Do you mean a cart with wheels?
No. By cart I mean more or less a sled.
Something with a flat surface?
Yes. It looks somewhat like a barge with a hull shape in the front. It's about 6 inches long and 4 inches wide. We take that cart and slide it over a layer of "sand" that is composed of really, really small glass beads. It's not like beach sand that's made of randomly sized and shaped grains.
Are the beads all the same size?
Yes. One of the things we're interested in is to determine what factors influence the motion of this cart. We change bead size to see what influence that might have. We change the rate at which we're pulling the cart and the weight of the cart itself. So we've been playing around trying to get an idea of what's really determining the motion of this cart.
Why do you use glass beads? Why not, for example, metal beads?
The advantage of glass is that it's transparent. One of the things we're interested in is using really high-resolution photography to look at the individual contacts between the glass beads and the plate itself and also into layers of the granular surface. With glass beads you have some visibility. Also with metal beads you run into problems with things like corrosion. And glass beads are really durable. They're less influenced by things like static electricity, something we try to avoid.
What's the composition of the cart?
We use four carts; on the bottom of each we affix a layer of beads creating a stiff granular layer.
So it's not a perfectly smooth flat surface?
No. The most important thing about a cart is what makes up its contact surface. We use the same beads as in the "sand" bed.
So you have one surface, the "sand" bed, where the beads can move among themselves, and then the surface of the cart where the positions of the beads are fixed.
Yes, we expect some rearrangement in the granular surface on the "sand" bed. But the beads are glued on to the bottom of the cart.
If you have perfectly round beads, each bead has only one infinitesimally small point of contact, right? So you're going to have them moving between actual contact with beads in the "sand" bed, and hanging in space between those beads.
That's something else that we're interested in looking at. Just what sort of contacts there are between the surfaces? If you think, for example, of a cart with a perfectly flat surface moving against another flat surface, you'd assume since it's solid on solid, there'd be a lot more contact than if it were grain on grain. With a grain on grain case, it's really not clear if the contacts themselves are directly correlated to the radius of each bead. One of the things we're hoping to do is look at the beads up close under a microscope to see how uniform their surfaces are. Are there imperfections in the surfaces that create a less obvious contact?
Where do you get the beads?
From industrial supply companies. Actually these beads are marketed for use in highway safety paint. They use them in the paint of highway signs to reflect the light from vehicles.
What kinds of implications does granular research have in an applied, real-world context?
The experiment we're doing mimics the interaction between continental plates in plate tectonics and interactions at fault lines. It may eventually be able to tell us something about earthquake dynamics. Studies of granular interaction can also be applied to avalanches. There are a lot of geophysical applications.
What's your take on the advantages and disadvantages of doing research as an undergraduate?
I think it's a pretty incredible experience, actually. I know from talking with other friends at different places that Clark seems to provide a fairly unique opportunity to take advantage of this kind of research as an undergraduate. It's a small enough school that you get a fair amount of attention as an undergraduate, particularly in a smaller department like the physics department. It's also large enough that it has a very active graduate research program. I think the opportunity to be able to take part in that is sort of unique to Clark.
I don't know that there are really any disadvantages. It's not something you're forced into; it's your choice. It takes up more of your time and energy, but it's something that you do because you want to and because it's just a really good experience.
I imagine it's fairly different from a classroom learning experience?
In a classroom you sort of idealize what you're doing. A lot of time the experiments you do in a science lab are designed to immediately display whatever phenomenon you're studying. With research there's theory that's applied to it, but it's not a direct application of any one idea. It requires a lot more thought, and searching for what exactly is responsible for what we're observing. In that sense it's a bit more like real life.