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Is a heat vs Mu chart Misleading? What factors into Mu? (brake pads)

  1. Jun 30, 2015 #1
    So I was trying to understand some Mu charts of Brake pads for cars.

    I thought that Mu was basically a "calculated, or measured constant " which could be used to compare friction between 2 materials. like a solid iron Rotor, and a brake pad. I was thinking that a simple chart that shows Mu throughout the operating temperature range was sufficient.

    My assumptions are that 1) Mu does not change with speed. whether a car is going 100 mph or 10 mph is irrelevant (rotor speed of 1333 RPM or 133 RPM) the Mu is the Mu .. Or am i wrong?

    total friction generated per minute would obviously go up, and heat would go up as a result which might push the pad/rotor combination into a hotter part of the chart, but the Mu would fall in line with its established value .
    Or does the mu change with speed ?

    2) assumption , Clamping force doesn't change Mu, as you clamp down harder, the total friction would go up, but not the actual Mu .

    If those assumptions are both correct, then someone Could look at a chart that shows Mu vs temperature and get a good idea of if brake pad A would perform better than brake pad B

    something that looks like this : 186751d1339888542-brake-pads-master-list-hawks.jpg

    Hopefully i'm not completely ignorant on this. i never took physics past high school, despite having a strong interest in it.

    But I want to know the correct answer.

    thanks in advance. :)
  2. jcsd
  3. Jul 3, 2015 #2
    Coefficients of friction are more sensitive to temperature than to speed.

    The idea that coefficient of friction is completely independent of speed is only approximate. Brake pads might have their frictional coefficient vary 10-20% over their speed range. In contrast, the variation with temperature is much larger.

    The idea that mu is perfectly independent of clamping force is also an approximation.
  4. Jul 7, 2015 #3

    was hoping for a yes/no kind of situation but that makes a lot of sense.
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