Minor Fixes

docs/physics/thermal/1-energy.md

@@ -138,4 +138,4 @@ Consider a piston with a compressable gas. In tthis case, with $\Delta x$ positi
 
 We know that the force exerted by the piston is equal to the pressure times the area. Thus, $W = P A \Delta  x$. But $A\Delta x$ is just volume (in this case, negative, as volume is decreasing). So, $W = -P \Delta V$.
 
-However, this assumes constant pressure. For a non-constant perssure, $P(V)$, we know that $W = \int F dx = - \int P(V) dV$.
+However, this assumes constant pressure. For a non-constant perssure, $P(V)$, we know that $W = \int F dx = - \int P(V) dV$.