Coefficient of friction different for different angles.

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Discussion Overview

The discussion centers around the measurement of the coefficient of static friction in two different experimental setups: one on a horizontal surface and another on an inclined ramp. Participants explore potential discrepancies in the measured coefficients and the implications of different experimental conditions.

Discussion Character

  • Experimental/applied, Debate/contested

Main Points Raised

  • One participant reports measuring a coefficient of static friction of 0.40 on a ramp and 0.25 on a horizontal surface, questioning whether this indicates a lab error or incorrect assumptions.
  • Another participant inquires about the measurement methods used in both experiments, seeking clarification on the experimental setup.
  • A participant describes the method for measuring friction on the horizontal surface, involving a forcemeter and plotting a friction graph to calculate the coefficient.
  • For the ramp experiment, the participant explains that they recorded the angle at which the block began to slide and calculated the coefficient using the formula mu = tantheta.
  • There is a question raised about whether the normal force was consistent across both experiments, implying it could affect the results.
  • Some participants note that the two surfaces (ramp vs. table) are different, which could contribute to the differing coefficients, and they confirm that the experiments were conducted a year apart.
  • One participant clarifies that the same surface was used for both experiments, despite the different setups.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the influence of different experimental conditions on the measured coefficients of friction. There is no consensus on whether the discrepancies are due to lab errors, differences in normal force, or other factors.

Contextual Notes

Participants have not resolved whether the differences in coefficients are due to experimental error, the nature of the surfaces, or the methods of measurement. The dependence on the normal force and the implications of using different surfaces remain unclear.

Hlud
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I am having my students do a lab to calculate the coefficient of static friction along a ramp. They are calculating the coefficient of static friction between felt and the table to be something like 0.40, yet when i did this lab, but along a horizontal surface, and not with a ramp, i get a coefficient around 0.25. Am i making a wrong assumption here, or am i making a lab error.
 
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How did you measure it, for each of the two experiments?
 
nasu said:
How did you measure it, for each of the two experiments?

For the first experiment, we dragged a block along the table, ever so slightly increasing the applied force (which is attached to a forcemeter) until it started moving. We plotted the graph, which clearly shows the friction graph, and calculated mu from there.

For this year's experiment, we increased the angle of the table, ever so slightly, recording the angle from our phones, until it just starts to slide. We then calculate mu using mu = tantheta.
 
The formula for friction coefficient involves the 'normal Force'. Was that the same for all experiments?
 
So the two surfaces were different, weren't they? The ramp is something else than the table, I understand.
And you did these experiments with one year interval in between?
 
nasu said:
So the two surfaces were different, weren't they? The ramp is something else than the table, I understand.
And you did these experiments with one year interval in between?

No, they were the same surface. And yes, the data was from last year.
 

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