Pitch

A shrill or piercing sound is also called a high-pitch sound.

We use one more term for shrillness - that is pitch. Shriller the sound, higher is the pitch.For example, compare the sounds of a buffalo and a goat. The sound of a goat is shriller than that of a buffalo. So, we can say that the goat has a high pitched voice and the buffalo has a low pitched voice.

Below is a video in which you can see the difference between a less shrill and a more shrill sound.

Video 2.2: Straw flute

We now know that sound is vibrations.

The number of times a particle/object vibrates in a second is called frequency.

If it vibrates more number of times in a given time, we say that its frequency is higher. Frequency of vibrations decide the pitch of the sound. Higher the frequency, higher is the pitch. Lower the frequency, lower is the pitch.

For further exploration:

What is the frequency of the rotation of ceiling fan?

As a ceiling fan speeds up, beyond a point we are not able to see its blades. This is a limitation of our eyes - we can't see things that move too quickly. So do the vibrations of sound also occur too rapidly for us to observe them. For example, if we look at a speaker (watch the video in 4.1), we can see that it vibrates but we are not able to count the number of times it vibrates in a given time.