An ambulance speeds past Ottoline on the sidewalk, siren wailing. As it passes, the siren's pitch drops, though the siren itself never changed.
The siren emits one fixed frequency. What Ottoline receives is another matter. This lesson names the effect.
Ottoline, the person receiving the sound, is called the observer.
While the ambulance moves, the frequency Ottoline receives is not the frequency the siren emits.
As the ambulance passes her, its motion flips from approaching to moving away, the received frequency changes, and she hears the pitch drop.
The siren's own frequency never changed. Only the motion between the source and the observer changed what arrived.
This change in the received frequency is called the Doppler effect.
Relative motion is the trigger: the source moving, the observer moving, or both.
With no relative motion there is no shift: a parked ambulance's siren arrives at exactly the frequency it emits.
A motorcycle rides past Noll at a steady speed, engine droning. Describe what Noll hears as it passes, and name the effect.
The motorcycle and Noll are in relative motion, so the frequency Noll receives differs from the frequency the engine emits.
As the motorcycle passes, its motion flips from approaching to moving away, and the received frequency changes.
Noll hears the drone's pitch drop as the motorcycle passes. The change in received frequency is the Doppler effect.
A train sits parked at a crossing with its bell ringing, and Pim stands still nearby. Does Pim receive a shifted frequency?
The Doppler effect needs relative motion between the source and the observer.
The bell and Pim are both at rest, so there is no relative motion.
No. Pim receives exactly the frequency the bell emits.
A fire truck drives past Maren with its siren on. What happens to the pitch she hears as it passes her?
Noll says: 'When a source of sound and an observer move relative to each other, the frequency the observer receives differs from the frequency the source emits.' Is Noll correct?
What is the change in received frequency caused by relative motion between a source and an observer called?
In which case does the listener receive a frequency different from the one the source emits?
An ice-cream truck drives toward Ottoline, its jingle emitted at one fixed frequency. Which statement is correct?
A hawk dives toward a field mouse, screeching as it comes. The screech frequency the mouse receives differs from the frequency the hawk emits. What causes the difference?