• bodaciousllam
In summary, the conversation is about a problem involving a pebble on a rotating wheel. The person asking for help has provided a diagram and attempted a solution, but is unsure if it is correct. Another person points out a small error and explains the concept of normal forces. The first person realizes their mistake and the conversation ends with a clarification on the direction of the friction forces.
bodaciousllam
I really have no idea if I even went about this problem right, maybe some of you wonderful people can help me out.

## Homework Statement

http://img217.imageshack.us/img217/9358/wheeljk9.jpg

## The Attempt at a Solution

http://img220.imageshack.us/img220/179/50999155cw8.th.jpg

Last edited by a moderator:
Welcome to PF! Your solution looks good! Note that the friction force in your diagram,
2(F_f), acts radially inward on the pebble; but you also show a friction force in what you are calling the 'theta' direction (parallel to the rotation axis), which is zero, because there is no acceleration in that direction.

Jay,

Thanks, but I can't figure out why the answer came out negative, unless it means I have the friction vectors pointing the wrong way, but that doesn't make sense to me intuitively.

And the theta friction force was just something I forgot to erase

Oh, yeah, I missed your minus sign. The plus and minus sign difficulties are typical of all Physics problems. Actually, as your sketch shows. there are 2 Normal forces acting on the pebble; they act in opposite directions, each pointing toward the pebble, so that one value is negative (-323 N), and the other is positive (+323 N). The normal forces act toward the object they act on. It's probably better to just give the magnitude of the normal force, and show the direction in a sketch. Note that the friction forces on the pebble act radially inward, as they must in order to keep the pebble moving in the circle, in the inward direction of the centripetal acceleration. When the static friction force is not sufficient to produce the inward centripetal acceleration, that is, when the rpm exceeds 4000rpm, the pebble is flung off in a direction tangent to the circular path.

## What is the purpose of studying dynamics in relation to rocks in tire tread?

The purpose of studying dynamics in relation to rocks in tire tread is to understand the behavior of rocks when they become embedded in the tread of a tire. This information can help improve tire design and safety, as well as provide insight into the mechanisms of rock movement.

## What factors affect the dynamics of rocks in tire tread?

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## How does the presence of rocks in tire tread affect vehicle performance?

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## What methods are used to study the dynamics of rocks in tire tread?

Scientists use a variety of methods to study the dynamics of rocks in tire tread, including laboratory experiments, computer simulations, and field studies. Each method has its advantages and limitations, and a combination of approaches is often used to gain a comprehensive understanding of the phenomenon.

## Are there any real-world applications of studying dynamics in relation to rocks in tire tread?

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