The frequency determines the shrillness or pitch of a sound. A drum vibrates with low frequency. Therefore, it produces low pitched sound. Whistle has a high frequency and therefore, produces a sound of higher pitch.

Amplitude of sound wave.

Ultrasound refers to sound that has a frequency above the audible range (20,000 Hz) of the human ear.

It is the eardrum which vibrates and sends vibrations to the inner air, when we hear any sound.

In most of the cases, we cannot see the vibrations because of its small amplitude.

(i) Oscillation: The to and fro motion of an object is called vibration. This motion is also called oscillatory motion.
(ii) Hertz : The number of oscillations per second is called the frequency in Hertz (Hz). A frequency of 1 Hz is one oscillation per second.

Major causes of noise pollution are sounds of vehicles, explosions including bursting of crackers, machines, loudspeakers, television and transistor at high volumes, some kitchen appliances, desert coolers, air conditioners, etc. All these contribute to noise pollution.

Yes, the frying pan will vibrate. Since, it is being hit by the stick but vibrations need a medium to travel and there is no medium in vacuum, so we cannot hear the vibrations produced.

Presence of excessive noise in the surrounding may cause noise pollution, which is harmful to human health. Here are some measures to limit noise pollution:
(i) Noise producing industries should be set up away from residential areas.
(ii) Silencing devices must be installed in aircraft engines, transport vehicles, industrial machines and heavy appliances.
(iii)Use of automobile horn should be minimized.
(iv) TVand music system should be run at low volumes.
(v) Trees must be planted along the sides of the roads and around buildings to cut down the sounds reaching the residents

In humans, the sound is produced by the voice box or the larynx. Put your fingers on the throat and find a hard bump that seems to move when you swallow. This part of the body is known as the voice box. Belowit is the windpipe. Two vocal cords, are stretched across the voice box or larynx in such a way that it leaves a narrow slit between them for the passage of air

When the lungs force air through the slit, the vocal cords vibrate, producing sound. Muscles attached to the vocal cords may make the cords tight or loose. When the vocal cords are tight and thin, the type or quality of voice is different from that when these are loose and thick.

We know that speed, pitch, loudness all are initiated with a vibration. During the day, there is a number of vibrations around us. So, the sound coming from the clock gets disturbed and amplitude of vibrations becomes small. But during the night, there are not such multiple vibrations in the environment. So, sound is more clear. Further, the dew factor at night increases the speed of sound as moisture level increases.