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Seconds after the fuse is lit, the firecracker disappears down the narrow metal-lined shaft while smoke trails behind it. The delayed explosion gives a striking sense of just how far the object has fallen beneath the surface.
When the firecracker detonates, its pressure wave travels through the confined shaft and reflects from the walls and other surfaces. Those reflected sound waves arrive back at the opening at slightly different times, creating the prolonged series of echoes heard above.
Deep vertical shafts can behave like enormous acoustic passages, allowing sound to travel considerable distances with complex reverberation. The demonstration makes the shaft's otherwise hidden depth and geometry perceptible through sound alone.
2026-08-08 03:00