P dV is mechanical work.

Work is energy, as the Work/Energy Theorem reminds us. Both have units of Joules.

So does torque, which is a little confusing, but also interesting. 1 Nm = 1 J. It results from radians being a dimensionless unit, so angular velocity squared has the same units as angular acceleration, which is not true for linear terms.

Defining radians: radius*{radians} = arc length
{radians} = {arc length} / {radius}
Both arc length and radius are measured in length, so the units of radians vanish:
[radian] = [m/m] = 1

So the angular velocity, squared has the same units as the angular acceleration:
[rad/s]^2 = [rad/s^2]
but this is not true for linear motion, because the numerator has non-vanishing units.
[m/s]^2 != [m/s^2]

Square brackets indicate I'm only talking about the units.

Like the pushing of a piston in a car engine. There's an increase in pressure due to the combustion, the piston moves, changing the volume, and the work (energy) transmitted to the piston is P(x) * A dx, since the area of the piston head is constant, and the changing volume is due to movement in 1-dimension. Here, P(x) is the pressure as a function of x, and A is the surface area of the top of the piston, dx is the distance traveled by the piston, due to the volume of the cylinder changing by a factor of ~7 in a gasoline engine, the pressure change is not negligible.

(The volume change is only more dramatic in diesel engines, which initiate combustion only by compression of the fuel-air mixture, without the injection of heat cause by a spark, so they need to compress the fuel-air more to achieve the heat needed for spontaneous combustion.)