sound is produced due to vibrating motion,then why doesnt a pendulum produce sound?

Answer 1

Because a pendulum moves too slowly.

The human ear can hear from about 20 cycles a second up to about 20000 cycles a second (in children) or 15000 cycles a second (in adults; as you get older, the upper limit falls).

The period of a pendulum is given by the formula T = 2 * pi * sqrt (L / g).
For 20 cycles a second (the lowest frequency you can hear) T = 1 / 20 = 0.05
so sqrt (L / g) = 0.05 / (2 * pi) = 0.007958
L / g = 0.0000633257
L = 0.0000633257 * 9.8 = 0.0006206 m.
= 0.6206mm.

A pendulum producing vibrations at the lowest pitch you could hear would have to be 0.6mm. long.

Answer 2

The pendulum doesn't move fast enough to produce a sound. Humans can only hear sounds which are 20 hz or above, which means 20 times a second. So, the pendulum would have to move 20 times a second for the human ear to hear a sound.