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!

How to notate a variable that is being held constant

  1. May 30, 2013 #1
    I remember learning at one point that you can put some sort of symbol on top or near a variable to indicate that it is being held constant. I thought that it was just a bar drawn above the variable but in some cases, it means "the average of."

    Anyone know what I'm talking about?
  2. jcsd
  3. May 30, 2013 #2
    Do you mean that, when taking a partial derivative and want to specifically keep t constant, you can write, for example, ##\left(\frac{\partial f}{\partial x}\right)_t##?
  4. May 30, 2013 #3
    No, I mean something much simpler. It's a symbol or notation that you'd use as you're explaining how variables will change relative to each other.

    Here's a very simple example using the equation d=vt (distance = speed*time):

    Say I want to hold the speed at a constant value; I now know that by increasing the amount of time, I'll increase the value of the distance by a proportionate amount. My question involves a short-hand symbol for indicating that the speed is the variable that's being held constant, instead of wasting time writing out "___ is constant" everytime I'm discussing an equation.
  5. May 30, 2013 #4
    In spreadsheet programs like excel this is done by putting '$' '$' around the variable, though I doubt that's what you're looking for.

    Do you mean just saying:
    ##D= \frac{v}{t} \rightarrow D= \frac{v_1}{t}##? Because that sort of does it.
  6. May 30, 2013 #5

    That's more like it, but not exactly what I had in mind.

    It's such a dumb little thing but it's driving me nuts.

    Thanks for the reply
  7. May 30, 2013 #6
    What class was it? That might help?
  8. May 30, 2013 #7
  9. May 30, 2013 #8
    It's not for a specific class. I tutor for math and physics and there are times when I want to denote which variable in the equation is being held constant for the sake of discussing how the other variables effect each other.

    I remember a math (or science) teacher I had in high school making a mark near the variable that would be held constant.
  10. May 30, 2013 #9


    User Avatar
    Homework Helper

    I'm not familiar with any standard notation that denotes what you want. You could make one up for the students you are tutoring, but let them know it's not a notation they're likely to see elsewhere.

    You could say something like "let d = x(t) = vt", where the function notation x(t) explicitly denotes that t is the variable. If the students need a mark to remind them which symbols are constants, function notation may at first be confusing for them, but it's a notation they will likely see again in the future.
  11. May 31, 2013 #10


    User Avatar
    Science Advisor

    If you are talking about the distinction between "dependent variables" and "independent variables", I am not familiar with any specific notation, but there is a common convention of formulating equations so that the dependent variable goes on the left and the independent variable or variables go on the right.
    Last edited: May 31, 2013
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook