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I'm studying engineering and there's a physics teacher that strikethroughs the derivative $d$ when writing an expression for power (which is work over time). I know physics teachers are known to abuse mathematical notation, but this intrigued me as I had never seen it used and couldn't find anything online. So the expression she writes is:

$đW/dt = ...$

What does it mean for the $d$ to be struck like this?

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I've seen this frequently in physical chemistry books. It's to remind you that this is an inexact differential that results in a path-dependent integral. So, for example, it would be used with $dq$ or $dw$, but not with $dE$ or $dS$. They call $E$ and $S$ state variables, but $q$ and $w$ are really not well-defined functions — they depend on the path/process, not just on the endpoints.

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  • $\begingroup$ Thank you for your answer. So does this notation have any use outside of physics/chemistry? Also, I assume $q$ refers to heat right? $\endgroup$ – Carlos Gruss Aug 13 at 20:15
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    $\begingroup$ I don't know other places. In math we will write $d\theta$ even though the polar coordinate is not globally defined; but here at least the differential is locally exact and independent of any choices. $\endgroup$ – Ted Shifrin Aug 13 at 20:18
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    $\begingroup$ I think the $\delta$ ($\delta Q$ and $\delta W$) is more common in physics (personally, I didn't see that kind of d before). $\endgroup$ – Botond Aug 13 at 21:11

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