For example, is the dV in the work integral (for work done "on" the system)
now changed from negative to positive ??? Or vice versa ??
This goes against the standard mathematical dV representing an "increase" in
V.
I guess I can live with, and teach, whatever the accepted convention is, but
I thought everything fit together kind of nicely the old way.
Oren Quist, SDSU
-----Original Message-----
From: Jeff Weitz [mailto:weitz@PIPELINE.COM]
Sent: Tuesday, July 03, 2001 9:49 AM
To: PHYS-L@lists.nau.edu
Subject: New AP Physics Convention in Thermodynamics
I certainly appreciate the intensity with which so many people respon=
d to questions, and also the discussions that evolve from those quest=
ions.
The College Board has changed a sign convention in thermodynamics as =
follows:
"Another change for 2002 relates to the sign convention used for work=
in thermodynamics. In thermodynamic equations, the symbol W will rep=
resent the work done on a system rather than by a system, so that the=
first law of thermodynamics will be written D U =3D Q + W. This chan=
ge makes the sign convention consistent with that used for work in me=
chanics, as well as with the thermodynamic convention used in most ch=
emistry and some physics textbooks."
Back in the stone ages, I was taught that W is positive when the gas =
does work, and I've taught it that way since. Now, of course, I can =
change, though I do like to write Q =3D W + D U. =20
What is the sense of the folks on this list? How widely is the new AP=
convention used as compared with the old one?=20
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<META content=3D"text/html; charset=3Diso-8859-1" http-equiv=3DConten=
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<BODY bgColor=3D#ffffff>
<DIV>Hi Everyone,</DIV>
<DIV> </DIV>
<DIV>I certainly appreciate the intensity with which so many people r=
espond to=20
questions, and also the discussions that evolve from those questions.=
</DIV>
<DIV> </DIV>
<DIV>The College Board has changed a sign convention in thermodynamic=
s as=20
follows:</DIV>
<DIV>
<P>"Another change for 2002 relates to the sign convention used for w=
ork in=20
thermodynamics. In thermodynamic equations, the symbol <EM>W</EM> wil=
l represent=20
the work done <U>on</U> a system rather than <U>by</U> a system, so t=
hat the=20
first law of thermodynamics will be written <FONT size=3D3><FONT=20
face=3DSymbol>D</FONT> <I>U</I> =3D <I>Q</I> + <I>W</I></FONT>. This =
change makes=20
the sign convention consistent with that used for work in mechanics, =
as well as=20
with the thermodynamic convention used in most chemistry and some phy=
sics=20
textbooks."</P>
<P> -from <A=20
href=3D"http://www.collegeboard.org/ap/physics/html/cours014.html";>ht=
tp://www.collegeboard.org/ap/physics/html/cours014.html</A></P>
<P> </P>
<P>Back in the stone ages, I was taught that W is positive when the g=
as does=20
work, and I've taught it that way since. Now, of course, I can =
change,=20
though I do like to write Q =3D W + <FONT size=3D3><FONT face=3DSymbo=
l>D</FONT>=20
<I>U. </I></FONT></P>
<P><EM>What is the sense of the folks on this list? How widely i=
s the new=20
AP convention used as compared with the old one? </EM></P>
<P> </P>
<P>Hope summer is treating everyone well,</P>
<P>Jeff Weitz</P></DIV></BODY></HTML>