Final answer:
You must yield right of way to an emergency vehicle by stopping and becoming stationary until it passes by. It is a matter of safety, law, and civility. Also, the Doppler effect determines siren frequency changes as an emergency vehicle approaches and recedes.
Step-by-step explanation:
When an emergency vehicle, such as an ambulance, fire truck, or police car, is sounding an alarm and flashing its lights, you must yield right of way by stopping and becoming stationary until it passes by. This ensures the safety of all road users and allows the emergency vehicle to proceed to its destination with the least amount of delay. This requirement is part of standard road safety regulations and traffic laws that aim to facilitate the urgent transit of emergency services. It is also a matter of common courtesy and civic responsibility.
Furthermore, the Doppler effect plays a role in identifying the approach and recession of an emergency vehicle's siren. While standing on the sidewalk, the frequency you observe will most closely match the actual frequency of the siren as it is coming toward you, because the sound waves are compressed as the source approaches, increasing the frequency. As the vehicle moves away, the frequency will seem lower due to the stretching of sound waves.