Alarm clock inside a bell jar. This illustrates an experiment to show that sound requires air for propagation. The alarm clock is allowed to ring whil

---

Alarm clock inside a bell jar. This illustrates an experiment to show that sound requires air for propagation. The alarm clock is allowed to ring while the air is evacuated from the bell jar. The ringing noise gets quieter until a vacuum is achieved, when it is silent even though the mechanism is working.

---

Size: 3632px × 4844px
Photo credit: © Science Photo Library / Alamy / Afripics
License: Licensed
Model Released: No

Keywords: acoustic, acoustics, air, alarm, analogue, bell, clock, demonstration, empty, enclosure, experiment, face, glass, hands, jar, muffled, muffling, noise, propagation, ring, ringer, ringing, silence, silent, sonic, sonics, sound, time, timepiece, vacuum, wave, waves