I just want to know if the pressure can be subtracted from pressure gradient. I did a google search and it didn't help me.

I know the question is silly and the answer to it should be no but at one place i read it can be subtracted so sorry if the question seems to be stupid and pls kindly help.

  • 2
    $\begingroup$ The question doesn't make sense to me: $P$ and $\nabla P$ don't have the same units, so they cannot be added... $\endgroup$ May 4, 2016 at 14:52
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    $\begingroup$ ... in other words: no you can't. $\endgroup$
    – garyp
    May 4, 2016 at 15:39

1 Answer 1


You cannot subtract a pressure from a pressure gradient because they have different dimensions. However suppose you express the pressure gradient as:

$$ \frac{dP}{dx} = \frac{P_1 - P_2}{x_1 - x_2} $$

then you can subtract some constant pressure $P_0$ from both $P_1$ and $P_2$:

$$\begin{align} P'_1 &= P_1 - P_0 \\ P'_2 &= P_2 - P_0 \end{align}$$

and your pressure gradient will be unchanged i.e.

$$ \frac{dP}{dx} = \frac{P_1 - P_2}{x_1 - x_2} = \frac{P'_1 - P'_2}{x_1 - x_2} $$


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