Piston effort=load due to gas alone?

[ajayguhan]

In my book it is mentioned that piston effort along the line of stroke=(Force due to gas pressure)+(Inertia force)

why we have to consider inertia force when it is a imaginary force which is considered only during non inertial frame?

why we don't equate piston effort with gas force simple (neglecting friction) why we have to consider inertia force?

 

[dean barry]

the work done during the power stroke is translated into motion energy whether that is just the piston / crank / clutch etc when idling, or including the remainder of the drive train and the vehicle itself when in gear.