Sound, Hearing, and Music

Sound begins with a vibration and needs matter through which to travel. Your ear then turns a changing pressure pattern into nerve signals that the brain interprets.

This lesson supports Chapter 15 of Physics for Beginners. Keep the physical picture in view, write the units, and check the direction of every vector before trusting a calculation.

Sound is a mechanical pressure wave

Sound cannot travel through a vacuum. In air, it moves as longitudinal compressions and rarefactions. Its speed depends on the medium and temperature. The familiar relation \(v=f\lambda\) still applies.

Frequency and amplitude shape what we hear

Frequency is closely related to pitch. Greater amplitude usually produces a louder sound, though perceived loudness also depends on frequency and the ear. Sound level is measured on a logarithmic decibel scale. A small numerical increase can represent a much larger intensity.

Resonance strengthens selected frequencies

A system responds strongly when driven near one of its natural frequencies. Strings and air columns support standing-wave patterns. Their allowed frequencies depend on length, tension, wave speed, and boundary conditions. The mix of harmonics helps distinguish two instruments playing the same note.

Worked example

A \(680\text{ Hz}\) sound travels at \(340\text{ m/s}\). Its wavelength is \(\lambda=v/f=340/680=0.50\text{ m}\).

Watch the idea in action

Khan Academy gives a focused explanation of the chapter’s central idea. Pause before each calculation and predict the next step on paper.

Practice questions

1. Can sound travel through a vacuum?
2. Is sound in air transverse or longitudinal?
3. What property is closely related to pitch?
4. What usually increases perceived loudness?
5. What is resonance?
6. Why can two instruments sound different on the same note?

Answers

1. No.
2. Longitudinal.
3. Frequency.
4. Greater amplitude.
5. A strong response near a natural frequency.
6. They produce different mixtures of harmonics.

Keep studying

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