What does a piston do?

• A. Store lubricating oil.
• B. Fit closely with cylinder, transfer force.
• C. Rotate to regulate temperature.
• D. Transmit electrical signals.

Answer: (B)

A piston is the moving boundary inside the engine cylinder that experiences the force from burning fuel. The high-pressure gas from combustion pushes the piston, making it slide up and down. This linear motion is then transferred through the connecting rod to the crankshaft, turning the gas’s energy into usable rotational power. The piston must fit closely with the cylinder wall and has rings to seal the combustion chamber and control oil film, while also conducting heat from the piston to the cooler cylinder wall. Lubricating oil isn’t stored in the piston; it circulates around it. The piston doesn’t rotate to regulate temperature, and it doesn’t transmit electrical signals.