Question

find the word that matches the definition: the tendency of sound from a moving object to change frequency relative to a stationary observer

Explanation:

The Doppler effect is a phenomenon in physics where the frequency of a wave (such as sound or light) changes for an observer moving relative to its source. In the context of sound, when an object (like a moving car) emits sound, the frequency heard by a stationary observer changes. If the object is moving towards the observer, the frequency increases (higher - pitched sound), and if it's moving away, the frequency decreases (lower - pitched sound). This matches the given definition about the tendency of sound from a moving object to change frequency relative to a stationary observer.

Answer:

Doppler effect