Look into a well and say your name out clearly, do you hear your voice again after a few seconds? This is commonly known as an echo. Technically, echos cannot be considered sound- but is actually a reflection of sound, arriving at a listener some time after the sound is produced.
ECHOES are formed when sounds are reflected off hard, flat surfaces like a large wall or a distant cliff. Besides the novelty of hearing your words repeated, echos can be used to measure distance by knowing the speed of sound and find the velocity of a moving object by using the Doppler Effect.
WHY DID WE HEAR THAT ECHO?
Sound is a waveform made from vibrating matter. The sound wave travels through matter—especially air—in a straight line. When the wave hits a different material, some of it is reflected, absorbed and transmitted through the material. In the case of a sound wave in air hitting a solid wall, most of the sound is reflected.
When a wave bounces off a moving object, the frequency of the sound changes according to the relative velocity of the object. The higher the frequency the higher the pitch.
If the wall is relatively flat, perpendicular to the source of the sound, and far enough away (but not too far), then you can hear the reflected waveform or echo. If the sound comes back in about 0.1 second or longer, you can readily distinguish the echo.
Since sound travels at approximately 300 meters per second and if the wall was, say, 15 meters away, the sound would return in 0.1 second. This can be seen from the relationship:
d = v*t or t = d/v
where
d = the distance the sound wave traveled back and forth,
v = velocity of sound, and
t = the time it takes the sound to go back and forth.
t = 30 m / 300 m/s = 0.1 sec.
(The distance was doubled to show the back and forth motion of the sound.)
That is enough time to be able to distinguish between the noises you made and the reflected sound, hence an echo could be heard. Similarly, by using the same formula, the distance from an object can be found by using the velocity of sound.
Interestingly enough, echoes can be used to find the velocity of a moving object by using The Doppler Effect.
If the object is moving toward you, the frequency or pitch of the sound gets higher. When it is moving away, the pitch gets lower. The faster the object is moving, the greater the change in frequency or pitch.
The Doppler Effect can be used to measure the velocity of an object by comparing the frequency of the sound sent out to the frequency of the sound reflected by in the echo.
Echos sound useful, don’t they! You may not have expected this, but echos are actually adopted in the use of Sound Navigation and Ranging (Sonars), which works by measuring the time it takes for sound to reflect off a surface like the sea floor and return as an echo. The longer it takes for an echo to return, the further away the reflective surface, like the sea floor to measure depth of the ocean.
Not only so, linking to the meat of this magazine, echolocation is also the system bats use to watch out for prey. To begin with, let us look at how bats detect sound, followed by how they use ultrasound to navigate around, especially in the darkness, since most bats are nocturnal.
Here is a video provided for a concise summary on Echoes! :)
(The distance was doubled to show the back and forth motion of the sound.)
Interestingly enough, echoes can be used to find the velocity of a moving object by using The Doppler Effect.
If the object is moving toward you, the frequency or pitch of the sound gets higher. When it is moving away, the pitch gets lower. The faster the object is moving, the greater the change in frequency or pitch.
The Doppler Effect can be used to measure the velocity of an object by comparing the frequency of the sound sent out to the frequency of the sound reflected by in the echo.
Echos sound useful, don’t they! You may not have expected this, but echos are actually adopted in the use of Sound Navigation and Ranging (Sonars), which works by measuring the time it takes for sound to reflect off a surface like the sea floor and return as an echo. The longer it takes for an echo to return, the further away the reflective surface, like the sea floor to measure depth of the ocean.
Not only so, linking to the meat of this magazine, echolocation is also the system bats use to watch out for prey. To begin with, let us look at how bats detect sound, followed by how they use ultrasound to navigate around, especially in the darkness, since most bats are nocturnal.
Here is a video provided for a concise summary on Echoes! :)
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