During the power stroke, what force acts on the piston?

During the power stroke, the force that acts on the piston is the force of expanding gas. In a small engine, the power stroke occurs after the ignition of the air-fuel mixture in the combustion chamber. As the mixture ignites, it creates a rapid increase in temperature and pressure, causing the gases to expand dramatically. This expansion pushes the piston down, converting the chemical energy from the fuel into mechanical energy.

Understanding the role of expanding gas is crucial because this is what generates the power needed to drive the engine. The pressure exerted by the gases must be sufficient to overcome resistance from other components, such as the connecting rods and crankshaft, to convert the linear motion of the piston into rotational motion.

Other forces, such as gravity and vacuum force, may have their own roles in the engine's function, but they are not the primary forces exerted on the piston during the power stroke. Pressure from oil is also significant in lubricating moving parts but does not directly contribute to the power generation process like the expanding gases do. Thus, the force of expanding gas is essential for understanding how an internal combustion engine operates during the power stroke.