Objective:
– To demonstrate that the pitch varies with the frequency of the source.
Apparatus:
- Rotor
- Rotating pitch disc (Savart’s wheel)
- Air hose with a jet
Method:
The air jet is moved along the rows of holes in the rotating disc to produce various tones.
Frequency and Pitch Generation:
- Fundamental Relationship: Pitch is directly proportional to frequency; a higher frequency of vibration produces a higher perceived pitch.
- Rotator Mechanism: A rotating disk (like a siren or Savart Wheel) with holes (ports) produces sound by chopping an air stream. The pitch is determined by the rotational speed (RPM) and the number of holes.
- Doppler Effect: As a rotor moves toward or away from a listener, the sound produced can shift in pitch due to the Doppler effect, specifically causing a momentary upward shift as the blade tips move toward the observer
Extra Resource:
Rotator Siren
– Video Created at the Smithsonian’s National Museum of American History.