Difference between revisions of "Work"

From SklogWiki
Jump to: navigation, search
(W=-pdV on compression or expansion, but always ''upon'' (I am 98% sure))
Line 1: Line 1:
The mechanical '''work''', ''W'', performed in ''compressing'' a gas is given by
+
The mechanical '''work''', ''W'', performed ''upon'' a gas is given by
  
 
:<math>W = - \int_\alpha^\beta p ~dV</math>
 
:<math>W = - \int_\alpha^\beta p ~dV</math>
  
 
where <math>\alpha</math> and <math>\beta</math> are points in state space, ''p'' is the [[pressure]]
 
where <math>\alpha</math> and <math>\beta</math> are points in state space, ''p'' is the [[pressure]]
and ''V'' is the volume.
+
and ''V'' is the volume. The mechanical work done ''by'' the gas has the opposite sign (a common
 +
source of mistakes).
  
For reversible changes
+
For reversible changes,
  
 
:<math>\left.dW\right.=-p~dV  </math>
 
:<math>\left.dW\right.=-p~dV  </math>

Revision as of 10:07, 8 June 2009

The mechanical work, W, performed upon a gas is given by

W = - \int_\alpha^\beta p ~dV

where \alpha and \beta are points in state space, p is the pressure and V is the volume. The mechanical work done by the gas has the opposite sign (a common source of mistakes).

For reversible changes,

\left.dW\right.=-p~dV

and for irreversible changes

\left.dW\right. > -p~dV