* Sound is a vibration: Sound is created by vibrations that travel through a medium, like air. These vibrations cause our eardrums to vibrate, which our brain interprets as sound.
* The vibrations stop: Once the source of the vibration stops, the sound stops too. There's no "sound" hanging around in the air after the source is gone.
* Echoes and reverberation: What we might perceive as sound lasting is actually echoes or reverberations. These are reflections of sound waves off surfaces, making the sound seem to continue for a short time.
* Recording and playback: We can record sound and play it back later, making it seem like the sound "lasts." But the recording is simply a representation of the original sound, not the actual sound itself.
In summary: Sound is a temporary phenomenon. The vibrations that create sound only exist while the source of the vibration is active.