coeffecient of kenetic friction.

[dstebbins]

I'm in high school, taking physics as an elective. We just got through talking about coeffecients of kenetic friction (when c=coeffecient, f=applied force, and w=weight, then on a horizontal plane, c=f/w). Different pairs of surfaces create different coeffecients of kenetic friction; for example, sandpaper and steel have a greater coefficient than ice and soap (duh).

 

My question: Is there any way to predict what the coeffecient between to surfaces without pushing someone over a horizontal surface and without just memorizing the coeffecients?

[EvoN1020v]

Without pushing someone over a horizontal surface would be a static friction. It keeps the object from slipping.

 

There's no way of knowing coefficient of friction without testing (i.e. pulling or pushing).

[Bignose]

There's no way of knowing coefficient of friction without testing (i.e. pulling or pushing).

 

That's not quite 100% true, there are researchers who study the molecular interactions between surfaces to try to predcit friction coefficients. Suffice to say, however, this kind of research will be well beyond a high school level physics class. And, the experiments needed to measure the coefficient of friction are rather easy and cheap to set up and perform, so in all practical cases, testing will be the way to find out the answer.

[psynapse]

That's a strange equation you gave there. I know the numbers work out in normal situations using weight and F applied but what if you approach the top of a ferris wheel spinning fast? what forces keep you on your seat. there is no applied and your weight is going to seem different as you near the top and you begin to feel wieghtlessness.

I go with Friction force and Normal Force. friction force always being an oppiisition force and the normal force would be the force exerted up on an object keeping it from `breaking`through the ground or seat or whatever.

[swansont]

That's a strange equation you gave there. I know the numbers work out in normal situations using weight and F applied but what if you approach the top of a ferris wheel spinning fast?

 

That would not be on a horizontal plane, which was a specific condition mentioned in the OP.

[dstebbins]

That's not quite 100% true, there are researchers who study the molecular interactions between surfaces to try to predcit friction coefficients. Suffice to say, however, this kind of research will be well beyond a high school level physics class. And, the experiments needed to measure the coefficient of friction are rather easy and cheap to set up and perform, so in all practical cases, testing will be the way to find out the answer.

 

What are you saying? Are you saying that I'm too stupid to understand it?

[swansont]

What are you saying? Are you saying that I'm too stupid to understand it?

 

How, pray tell, did you reach the point where you had to clarify this, from Bignose's post?

[EvoN1020v]

That's a strange equation you gave there. I know the numbers work out in normal situations using weight and F applied but what if you approach the top of a ferris wheel spinning fast? what forces keep you on your seat. there is no applied and your weight is going to seem different as you near the top and you begin to feel wieghtlessness.

I go with Friction force and Normal Force. friction force always being an oppiisition force and the normal force would be the force exerted up on an object keeping it from `breaking`through the ground or seat or whatever.

 

 

The tension of the seat joined to the Ferris Wheel keeps it from falling off. Also, you don't use "Force applied" when you're defining forces in circular motions. Tension is another kind of force that points toward the centre. You'll learn it soon enough.

[J.C.MacSwell]

The tension of the seat joined to the Ferris Wheel keeps it from falling off. Also, you don't use "Force applied" when you're defining forces in circular motions. Tension is another kind of force that points toward the centre. You'll learn it soon enough.

 

Tension can point toward the centre but depends on the structure as well as the external forces.

[Bignose]

What are you saying? Are you saying that I'm too stupid to understand it?

 

In addition to what swansont said, beyond the level of a high school physics class speaks for itself. That means, you will not cover the necessary material to read a journal article that discusses the research. In fact, unless you are an active researcher in the area, virtually no one will have enough background necessary to read a recent paper and get much more out of it than a summary. What this means is that once you take at least a university level class, maybe even a graduate level physics class, then you will be at the level to get a lot more out of the paper, and understand what the researchers are doing.

 

Next time you think you are being insulted, sit back, relax, and understand that tone does not carry well over the Internet, via the written word. I in no was was trying to tell you that you were stupid, but you said you were taking high school physics and at that level you will not be able to understand the math and discussion in a peer-reviewed scientific journal like Journal of Tribology for example. (where if you really want to look see http://cat.inist.fr/?aModele=afficheN&cpsidt=7227671 ) Look, there are many, many topics discussed on this board that are well beyond my level. What that says about my stupidity I suppose is up to you to decide, but I have never looked at a quantum mechanics book, and only when I studied tensors I saw a tiny bit about relativity. That does not mean I couldn't undersand it, but it would take me quite some time to get to a level where I could read a current QM or special relativity (or many, many other subjects) research paper and get anything whatsoever out of it. I would and do fully accept the fact that someone would and should tell me that QM is above my level right now.