Have you ever wondered why the whistle of a traveling, distant locomotive predicts its approach

several yards before anyone actually sees it? Or why an oncoming ambulance’s screaming siren

is heard momentarily several feet before the ambulance comes into full view, before it passes

you, and why its siren is still heard faintly well after the ambulance is out of sight?

What you are witnessing is a scientific phenomenon known as the Doppler Effect. What takes

place is truly remarkable. In both of these instances, when the train or ambulance moves toward

the sound waves in front of it, the sound waves are pulled closer together and have a higher

frequency. In either instance, the listener positioned in front of the moving object hears a higher

pitch. The ambulance and locomotive are progressively moving away from the sound waves

behind them, causing the waves to be farther apart and to have a lower frequency. These fastapproaching modes of transportation distance themselves past the listener, who hears a lower

pitch.

1. Which statement is not listed as a detail in the passage?

A. The oncoming sound waves have a higher pitch because of high frequency and closeness

of waves.

B. The oncoming sound waves have a higher pitch because of low frequency and closeness

of waves.

C. The whistling sound of the locomotive as it approaches and passes can be explained by

the Doppler effect.

D. The high-pitched sound of the ambulance as it approaches and passes can be explained

by the Doppler effect.

2. What is the main idea of the passage?

A. Trains and ambulances make distinctly loud noises.

B. Low-frequency waves make high-pitched sounds.

C. High-frequency waves make low-pitched sounds.

D. The Doppler Effect explains the rationale for why sound is heard initially more strongly

and then faintly after a moving object has passed.