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What does Δx mean?

  1. Sep 26, 2011 #1
    So I'm aware that the triangle is uppercase delta which means the difference between: 10[itex]\Delta[/itex]5=5

    But what does Δx mean?
  2. jcsd
  3. Sep 26, 2011 #2


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    It means the difference between two values of the variable x, between two specified events.
  4. Sep 26, 2011 #3
    It means the change in x. For x(at event 1) = 2 and x(at event 2) = 4 : delta x = 4-2 = 2
  5. Sep 26, 2011 #4
    sometimes it is also used to refer to uncertainty in the variable x
    what kind of "uncertainty" depends on the context: experimental, or pertaining to it being defined, ...
  6. Sep 26, 2011 #5
    Actually I've never seen that use of it. I'm not saying it's wrong, but it's unusual.

    But in elementary math texts, [itex]\Delta[/itex]x means the amount of change in the variable x. For example, the slope of a line is [itex]\Delta[/itex]y/[itex]\Delta[/itex]x, i.e. the change in y divided by the change in x, for any two points on the line.

    When you learn calculus, you will see that the instantaneous velocity of an object travelling along the x-axis is the limit of the displacement divided by the elapsed time, [itex]\Delta[/itex]x/[itex]\Delta[/itex]t, as [itex]\Delta[/itex]t approaches zero.
  7. Sep 26, 2011 #6
    It's already been answered pretty good. But just to clarify:

    [itex]\Delta[/itex]x = x[itex]_{2}[/itex]-x[itex]_{1}[/itex]

    or the slope of a function:
    [itex]\frac{\Delta y}{\Delta x}[/itex] = [itex]\frac{y_{2} -y_{1}}{x_{2}-x_{1}}[/itex]

    Which you'll find to be very similar to the definition of a derivative in calculus:
    [itex]\frac{\delta y}{\delta x}[/itex] which basically means (difference in y)/(difference in x)

    Capital delta is looking for a specific answer (most times) while lower case is looking for another equation (most times).
    Last edited: Sep 26, 2011
  8. Sep 27, 2011 #7
    What book would provide me with a quick reference to the use of greek letters in Physics?
  9. Sep 27, 2011 #8


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    Most symbols have different meanings in different contexts. Pi is one of the few symbols that has a consistent meaning.
  10. Sep 27, 2011 #9
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