Question

Ehy does vibrating simple pendulum not produce any sound

Answer 1

because there no frequency

Answer 2

If something vibrates at a frequency of or in between 20Hz to 20KHz, we can hear it otherwise we can't. because our ear can hear only this frequency range. OK, now according to this question the oscillation of pendulum is lees than the 20Hz(e.i. ... that's why we can't hear the sound of pendulum oscillation.