多普勒效应 - II

When a fire truck approaches, sound waves bunch up, creating an upward shift in frequency interpreted as high pitch. Conversely, when it recedes, waves spread out, causing a downward frequency shift heard as low pitch. This change in observed frequency occurs because the source moves relative to the stationary observer.

When an observer moves toward a stationary sound source, they strike more wave crests per unit time, resulting in high-frequency sound. When moving away, they strike fewer wave crests, producing lower frequency sound. The relative motion between observer and source determines the observed frequency change.

The Doppler effect occurs in two cases: first, when the source moves toward or away from a stationary observer, and second, when the observer moves toward or away from a stationary source. In both scenarios, relative motion between source and observer causes a shift in the observed frequency of sound waves.

Meteorologists use Doppler radars that emit radio waves toward the sky. These waves reflect off clouds and precipitation, returning to the station. If reflected waves show decreased frequency, clouds are moving away; increased frequency indicates approach. This technology determines wind speeds and direction based on frequency shifts.

A Doppler echocardiogram channels sound waves into the heart where they reflect off moving blood cells. Cardiologists analyze frequency shifts in reflected waves to determine blood flow speed and direction through the heart and vessels. This helps identify obstructions and assess cardiac function.

Sound waves bunch up when a source approaches, decreasing wavelength and increasing frequency, perceived as higher pitch. When the source recedes, waves spread out, increasing wavelength and decreasing frequency, perceived as lower pitch. The physical compression or expansion of waves directly alters the frequency reaching the observer's ear.

The Doppler effect enables cardiologists to assess blood flow in the heart by measuring frequency shifts of reflected sound waves. Like Doppler radar technology, frequency changes reveal blood flow speed and direction, allowing detection of obstructions or abnormalities in cardiac vessels and chambers.