1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Little math help here?

  1. Apr 26, 2010 #1
    Hey guys, I am a sophomore college student studying Aerospace Engineering and I am doing an experiment, and i ran into a little math problem that i can't seem to visualize properly.

    I have a y axis where which is a measure of pressure (from 0~200 bars), but expressed in voltages (1 to 5 volts).

    In order to properly analyze the results, i have to linearly transform the 1~5 volt scale to a 0~200 bar scale.

    I know it involves simple pre-calculus (with the y=mx+b) stuff but I just can't remember whatever I did in high school.

    Can anyone help me out here?

    Thanks in advance
  2. jcsd
  3. Apr 26, 2010 #2


    User Avatar
    Science Advisor
    Homework Helper

    The formula y = mx + b you gave is for a straight line, i.e. a linear dependence. For this application, let me rename y to P (for pressure) and x to V (for voltage): P = m V + b.
    What you can do now, is simply plug in two points that you want to correspond. For example, if 1 volt corresponds to 0 bar, set V = 1, P = 0 to get
    0 = m 1 + b = m + b
    Take another point, for example to let 5 volts correspond to 500 bar, set V = 5, P = 500:
    500 = 5m + b.

    This gives you two equations from which you can solve m and b (for example, the first one gives you b = -m, plugging that into the second one produces 500 = 5m - m = 4m and then you can find m).

    (Note that there are faster ways, such as calculating m = delta P / delta V = (200 - 0) / (5 - 1) = 200 / 4 = 50 and then plugging in one point, but this one is more general).
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook