17 - Vibrations and Sound

Frequencies which are multiples of a certain frequency are called overtones of that frequency

*The loudness of a note depends on the amplitude of the sound wave. The greater the amplitude the greater the loudness

*The pitch of a note depends on the frequency of the sound wave. The higher the frequency, the higher the pitch

*The quality of a musical note depends on the number of overtones present in the note and the relative strengths of the different overtones present

The highest and lowest frequencies that can be heard by a normal human ear. The range is 20 HZ - 20,000 HZ

The transfer of energy between 2 bodies of the same natural frequency

sound intensity at a point is

the rate at which sound energy is passing through unit area at right angles to the direction in which the sound is travelling at that point

The smallest sound intensity detectable by the average human ear at a frequency of 1 kHz. Its value is 1 × 10⁻¹² W m⁻²

Sound intensity level is measured in decibels (dB)

The frequency at which a body tends to vibrate if free to do so

A string vibrating with an antinode at it's centre and a node at each end is vibrating at its fundamental frequency

Frequencies which are multiples of a certain frequency f are called harmonics.
f is called the fundamental frequency or the first harmonic. 2f is the second harmonic, 3f is the third harmonic, etc.

• Person on a spring being pushed every time they move away
• Barton's pendulumns (LEARN)
• Glasses shattering with high pitched notes
• Column of air in a tube resonating with a tuning fork
• Buildings in an earthquake

*When the sound intensity (in W m⁻²) doubles, sound intensity level increases by 3 dB.

All harmonics

Odd numbered harmonics only

Learn about it

*mass per unit length