What effect does the expanding combustion gases have on the piston during the power stroke?

During the power stroke of an internal combustion engine, the combustion gases that result from the ignition of the air-fuel mixture expand rapidly due to the high temperature and pressure generated by the combustion process. This expansion exerts a force on the piston, driving it downward in the cylinder.

The downward movement of the piston is a critical part of the engine's operation, as it translates the energy produced from the combustion of fuel into mechanical energy. This mechanical energy is what ultimately powers the engine and propels the vehicle or equipment it is designed to operate.

The other options do not accurately describe the interaction between the expanding gases and the piston. For example, suggesting that the gases inhibit upward motion or create a vacuum effect contradicts the fundamental physics of the power stroke, where the focus is on the forces created by rapidly expanding gases. Additionally, the claim that expanding gases help to cool the engine is misleading, as the combustion process generates heat, which requires appropriate cooling measures to be effective.