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If you've ever been standing by the side of
the road as a speeding ambulance approached, siren wailing,
you may have experienced the Doppler Effect. As you stood
still, you heard the wail of the siren, a high-pitched
noise. As the ambulance came up beside you, the sound of the
siren changed to a much lower pitch. |
| You can also experience the Doppler Effect by
riding your bicycle at a constant speed past a blaring
building alarm. As you approach the building, the perceived
sound of the alarm sounds high-pitched. Just as you reach
the building, the sound of the alarm is reduced to a lower
pitch. |
| In the ambulance example, the source of the
sound waves was moving and the observer of the sound was
stationary. In the bicycle example, the source of the sound
waves was stationary and the observer of the sound was moving. |
| The Doppler Effect is the change in frequency
of energy waves when the source of or observer of the waves
is in motion. The frequency of sound waves determines their
pitch. Therefore, the high-pitched and low-pitched sounds
have different frequencies. |
| The Doppler Effect happens with radio waves in
the same way as with sound waves. Specifically, Doppler
RADAR transmits radio waves and uses the principles of the
Doppler Effect to calculate the speed and direction of
moving objects, like raindrops in a thunderstorm. Doppler RADAR allows
meteorologists to calculate not only the location of storms,
but the speed and direction of the winds within a storm as well.
Doppler RADAR has
significantly improved the forecasting of severe weather events. |
| Besides being a valuable tool for
meteorologists, the Doppler Effect is also used by astronomers to
calculate the distances to stars and their ages. Clearly, the
Doppler Effect is helping scientists better understand the
natural world. |
