Beats occur when two sounds of different frequencies are heard together, causing the amplitude of the combined sound wave to rise and fall due to interference. When tuning a piano, tuners compare the sound of each key to a tuning fork to check if they have the same frequency. If not, beats will occur until the piano wire is adjusted to match the fork's frequency. For two guitars playing tones of 397Hz and 425Hz, a listener would hear beats occurring at a frequency of 28Hz, calculated by taking the difference of the two frequencies.

1. A crash course in
Beats
Picture from textbook P. 253

2. What is a beat?
• When we hear 2 sound waves with different frequencies,
we hear beats
• This is due to the changing wave amplitude because of
destructive and constructive interference
Picture from textbook P. 249

3. Equations
Picture from textbook P. 251

4. Tuning a Piano
• Tuning a piano actually uses physics!
• Piano tuners compare the sound of a piano key with the
sound of a tuning fork
• If they don’t have the same frequency, the piano wire
has to be adjusted until the beating sounds stop
Picture from computer clip art

5. Question
• At a concert, one guitar has a tone of 397 Hz and another
has a tone of 425 Hz
• What beat frequency does a fan hear?
Picture from textbook P. 238

6. Answer
The beat frequency heard is:
425 Hz – 397 Hz = 28 Hz
Pictures from computer clip art

7. Answer
The beat frequency heard is:
425 Hz – 397 Hz = 28 Hz
Pictures from computer clip art