Concept
The audience will hear the buzzer’s stationary frequency shifted up as the ball moves toward them, and down as the ball moves away. The shifted frequency is given by:
$$ f' = \frac{v}{v \pm v_s}f$$
where $v =$ 343 m/s , $\pm$ means source moves away from or toward the observer, and $f =$ 4.0 kHz. With the ball moving at $v_s \approx 5 \text{m}/\text{s}$, the frequency shift, although no more than a few percent, is still clearly perceived.
Procedure
- Unzip ball, turn on buzzer, and re-zip ball.
- Throw the ball a student located in the middle of the classroom.
- Have that student throw the ball to another student
- Ask the students to report whether they heard a higher or lower frequency than when the ball was stationary.
- Discuss the correlation between the motion/location of the ball and their reports of frequency changes.
Equipment
- Foam Ball
- Buzzer (4 kHz)