I have two equations:

(1) $\displaystyle y = \frac {0.0060}{k}$

(2) $\displaystyle y= \frac{0.00016}{m}$

In the first equation, $k$ is held constant and in the second equation, $m$ is held constant.

How do I determine which variable has a greater affect on $y$?

E.g., how do I determine if doubling $k$ as a greater effect on $y$ than doubling $m$ and so forth?


  • $\begingroup$ If k and m are held constant, then y in each equation does not change. $\endgroup$ – Ross Millikan May 21 '11 at 20:16

Dear user, both relationships are called "inverse proportionality", so they have exactly the same effect: doubling of $k$ in the first case as well as doubling of $m$ in the second case reduces $y$ to one-half of its value.

  • $\begingroup$ Thanks @Lubos, so there is no other way in which you would comment on how m and k affect y differently? $\endgroup$ – user10265 May 21 '11 at 12:17
  • 2
    $\begingroup$ @user10265: As was pointed out above, if $m$ is doubled, the relative change is the same as when $k$ is doubled. The absolute changes are different, but in most physical situations it is relative change that matters. To calculate absolute change, find the difference between $y$ at $m$ and $y$ at $2m$, and do the same for $k$ and $2k$. Which absolute change is bigger and which is less will depend on the values of $m$ and $k$. So the most you can say if you use absolute change is "it depends." $\endgroup$ – André Nicolas May 21 '11 at 14:02

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