What is the function of pistons in an internal combustion engine?

Major moving parts of a piston engine: (1) PISTONS — slide up and down in cylinders; compress mixture; receive force from combustion; equipped with PISTON RINGS that seal against the cylinder wall, control oil, and conduct heat to the cylinder; pistons made of aluminum alloy (light and conducts heat well); (2) CYLINDERS — bored holes in the engine block where pistons travel; cylinder walls finished to specific tolerances; (3) CONNECTING RODS (CON RODS) — link pistons to crankshaft; convert piston's linear motion to crank's rotational motion; (4) CRANKSHAFT — rotating shaft; offset journals (crankpins) attach connecting rods at different positions, creating rotational motion; bottom of engine; (5) CAMSHAFT(s) — operates valves; can be in the block (OHV/pushrod engines) or in the cylinder head (OHC/overhead cam, more common today); SOHC = Single overhead cam, DOHC = Double overhead cam; (6) VALVES — control flow of air-fuel mixture IN (intake valves) and exhaust OUT (exhaust valves); typical modern engine has 2 or 4 valves per cylinder; (7) TIMING BELT or TIMING CHAIN — connects crankshaft to camshaft, keeping their rotation synchronized; (8) FLYWHEEL — heavy disk on crankshaft; stores rotational energy between power strokes; smoothens power delivery; on manual transmissions, the clutch engages with the flywheel. Engine displacement: total volume swept by all pistons = (π × bore²/4) × stroke × number of cylinders. Typically quoted in liters (L) or cubic inches (CID); 2.0L engine = 2000 cc. Bore = cylinder diameter; stroke = piston travel distance. Engines are classified by configuration: INLINE (cylinders in a row, like I4, I6), V (two banks of cylinders in V-shape, V6, V8, V12), FLAT/BOXER (opposed cylinders, used by Subaru, Porsche), W (multiple V banks). More cylinders generally = smoother running but more complex and heavier.