Working out Coefficient of Friction HELP

In summary, the student is trying to find the static coefficient of friction, which is different from the kinetic coefficient. He is also trying to find out how to find the kinetic coefficient without knowing the static coefficient.
  • #1

Homework Statement

For my Year 12 Physics EEI (Yes I have already asked for help about the actual prac, but now I'm onto writing up the theory:wink:) I conducted a prac where I rolled a fishing sinker down a 1.2m length of pipe into a tray of flour. I am now trying to use all relevant theory for the write up. I have been told (by classmates not the teacher) that as part of my theory I need to include the force of friction equation.

Homework Equations

I can work out the Normal force, by using the eqn Fn=mg, but without knowing Fk (or Fs, but I said Fk because the sinker is rolling down the pipe, not stationary), or u (coefficient of friction, sorry I didn't use the correct symbol) how can I work out u? How can I find it with only knowing one variable?

The Attempt at a Solution

I found the rearranged formula and it seemed simple enough: u =Fk/N, but as I said there are too many variables. I know the weight of the sinker, the lengths of the "ramp" (being the pipe) and the distance along the ground, and the angle.

How is it that I use cosine in working out in this formula? Sorry I know this is a basic question but we haven't done this work in class for about year, still no excuse though. :frown:

Any help is thoroughly appreciated :smile::biggrin:
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  • #2
The normal force is not just mg. It's the component of the vertical force mg that is normal to the pipe. If the angle of the pipe is 't' with respect to the horizontal, then that's mg*cos(t).
  • #3
So does mg*cos(72) = the Normal force? Or is it the force of friction? That gives 307.83. Is this Newtons? I'm assuming it is.

Thank you for your help =) .
I should be understanding this. Grr.
  • #4
Normal force, if 72 degrees is the angle between the pipe and the horizontal. Didn't I say that? For example if the angle were 90 degrees, then the pipe would be vertical, so no normal force (since cos(90 degrees)=0).
  • #5
OK yep, sorry, yes I get that now.

From there I can go Us = sin 72 degrees / cos 72 degrees = (which is the same as) tan 72 degrees = 3.077 (Static Coefficient).

How different is the static coefficient from the kinetic, and how do I then work that out?

Wait...because my angle is measured when the object was moving, not just starting to, does that mean that I have already worked out the kinetic and it is infact kinetic not static friction?
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  • #6
Yes, if it's moving it's kinetic.
  • #7
Thank you so much, sorry my question and answers were frustrating, thank you for continuing to help me.:shy: :approve::biggrin:

1. What is the coefficient of friction and why is it important?

The coefficient of friction is a measure of the amount of resistance between two surfaces in contact. It is important because it helps determine the amount of force needed to move an object over a surface, and is essential in understanding the behavior of objects in motion.

2. How do you calculate the coefficient of friction?

The coefficient of friction is calculated by dividing the force required to move an object by the weight of the object. This can be done using a variety of methods, including using a force sensor or by measuring the angle at which an object starts to slide on an inclined plane.

3. What factors affect the coefficient of friction?

The coefficient of friction can be affected by several factors, including the type of surfaces in contact, the roughness of the surfaces, the force applied, and the presence of lubricants. The type of material, temperature, and humidity can also play a role.

4. Why does the coefficient of friction vary for different surfaces?

The coefficient of friction varies for different surfaces because of differences in their physical properties. Smooth surfaces tend to have a lower coefficient of friction compared to rough surfaces. The type of material and the presence of lubricants can also significantly affect the coefficient of friction.

5. How can knowledge of the coefficient of friction be applied in real-life situations?

Knowledge of the coefficient of friction is essential in various fields, including engineering, physics, and sports. It can be used to design machinery and structures that require specific amounts of friction, predict the behavior of objects in motion, and improve the performance of athletes by selecting the appropriate materials and surfaces for their equipment.