Final answer:
A torsional vibration is responsible for sending pressure waves along the crankshaft, creating the longitudinal waves we perceive as sound.
Step-by-step explanation:
A torsional vibration sends pressure waves moving back and forth along the crankshaft. When a vibrating string or object, such as a tuning fork, violin string, or loudspeaker produces sound, it creates longitudinal waves in the surrounding medium. These sound waves consist of compressions and rarefactions moving out with the same frequency as the vibrating source. The movement of the particles of a medium during the passage of a sound wave is a type of simple harmonic motion, and sound waves can be categorized into both transverse and longitudinal waves, depending on the type of medium and motion.