# International System Units

Discussion in 'Homework Help' started by Alfa_ET, Dec 8, 2011.

1. ### Alfa_ET Thread Starter New Member

Feb 26, 2011
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What is the partial derivative of pressure (bar) with respect to time?

is it m^3/s?

2. ### t_n_k AAC Fanatic!

Mar 6, 2009
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If 1 bar = 100kPa where the Pascal [Pa] is the SI unit of pressure then presumably the unit for the time derivative (rate of change) of pressure is $P_as^{-1}$

$1 \ P_a=1 \ kgm^{-1}s^{-2}$

So presumably the unit of the time derivative of pressure in terms of the fundamental units is

$kgm^{-1}s^{-3}$

3. ### Georacer Moderator

Nov 25, 2009
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Actually, I think it is $\frac{\partial P(bar)}{\partial t}=100k \cdot (-2) kgm^{-1}s^{-3}$
given that the formula for the pressure is as you say.

4. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
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If the question was actually about conversion between units then perhaps more succinctly

$1 \ Bars^{-1} \ <=> \ 100 \ kPas^{-1} \ <=> \ 10^5 \ kgm^{-1}s^{-3}$

I doubt the OP has any real ongoing interest in this matter.

5. ### Georacer Moderator

Nov 25, 2009
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Now I saw the units reference. It was me who had the brain dead moment after all. Sigh...