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A piston is a crucial reciprocating component in internal combustion engines, compressors, and pumps. It forms a movable boundary within the cylinder, sealed by piston rings, converting the energy from expanding combustion gases into mechanical motion. The piston's movement creates compression, combustion, and exhaust cycles while transferring linear force to the crankshaft through the connecting rod.

The piston operates on the reciprocating motion principle within a sealed cylinder. During the engine cycle: 1) Intake stroke - piston moves downward, creating vacuum to draw air-fuel mixture; 2) Compression stroke - piston moves upward, compressing the mixture; 3) Power stroke - ignited mixture expands, forcing piston downward; 4) Exhaust stroke - piston moves upward, expelling combustion gases. This linear motion converts thermal energy into mechanical work.