Sound: Definition, Influences, Pitch & Volume

Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

What is a sound? Learn about sounds and what influences how we perceive them, including pitch and volume. Test your understanding of sound features and finish off with a quiz.

What is Sound?

Have you ever wondered how or why things make sounds? Sound comes so naturally to us, from our very first year of life, but many of us don't stop to think about what it really is. It turns out that sound is a wave. But what exactly is a wave?

A wave is a vibration in space and time. The material vibrates up and down over a period of time. A sound is a specific type of wave that takes the form of vibrations traveling through air, water, or any other material. From a human perspective, sound is distinctive because of the way we perceive it. Sound is detected by our eardrums. When a sound passes through the air in the form of vibrations, those vibrations eventually make their way to our ears. When they do that, they cause our eardrums to vibrate, which sends electrical signals to the human brain. Our brains perceive these electrical signals as sounds.

But it's a bit more complicated than that, because no two sounds are the same. A sound can be quiet, or it can be loud. A sound can be high-pitched - like a squeaky voice, or it can be low pitched and booming, like a foghorn. So what, other than our perception, decides what a sound will be like?

Factors That Affect Sounds

There are many factors that affect sounds. The most important ones are frequency (or pitch) and volume. The shape of the wave decides these features. Frequency is how high or low a given sound is. A high-pitched or high-frequency sound is like a high note on a piano. A low pitched or low-frequency sound is like a bass drum or rumble. And then there's everything in between. Frequency is measured in hertz. For example, the A note above middle C is defined as 440 hertz. In wave form, a high-frequency sound is one where there are many waves each second. A low-frequency sound is the opposite, where there are very few waves that pass by each second. Here's what different frequencies of a wave look like:

Wave frequencies, lowest at top
Wave frequencies, lowest at top.

And then there's volume. A high-volume sound wave is one we perceive as being loud, like an airplane. A low-volume sound wave is perceived as quiet, like a rustling of leaves. When it comes to the wave itself, a high-volume wave has a high amplitude. The amplitude is the height of the wave from the rest position.

Amplitude of a wave
Amplitude of a wave

Here, for example, is a low-volume and high-volume wave:

Low and High Volume Waves caption=

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