ECHOES By: Courtney Pease, Lauren Kranawetter, and Mayra Gonzalez

 In Greek Mythology, Echo is a mountain Nymph. She assisted Zeus in an amorous adventure by distracting Hera with her story telling chatter. Hera discovered their scheme and made it so Echo couldn’t speak except to repeat another’s last words.  Pan falls in love with Echo but she rejects him. Being denied causes Pan to order sheppards to tear her to pieces. Her limbs were scattered and buried. She is everywhere and will repeat the last words of anyone who raises their voice. DID YOU KNOW?? 2

 An echo is the reflection of a single sound source.  Echoes can be used to estimate the distance of an object, its size, shape and velocity.  Animals use echo techniques to figure out the distance of their prey. ECHO 3

 Echoes are simply sound waves that are bounced back to the sound source. When you yell out or speak, your voice box creates vibrations in the air that are transmitted outwards. This is known as sound. If you are in an area with lots of things, the vibrations in the air hit all the objects in the room and dissipates. If you are in an open area, however, there is nothing for the sound waves (or air waves) to hit and become dissipated. So they travel and when it hits a wall, the sound comes back to you creating an “echo.” 4 ECHO

 The reason that you hear the echo half a second after you yell out is because air travels at a certain speed, and the difference in the times from when you yell out to when you hear your echo is the time it took the sound wave to travel from your mouth, to the far away walls, and come back to hit your eardrums which your brain interprets as sound. 5 ECHO

Since sound travels at approximately 1000ft/s (300m/s) and if the wall was 50ft (15m away), the sound would return in 0.1 second. This can be seen from the relationship: d = vt or t = d/v Where d = the distance the sound wave traveled back and forth. v = the velocity of sound t = the time it takes the sound to go back and forth. HEARING ECHOES 6

t = d/v d=15m v=300m/s Therefore, t = 30m / 300m/s = 0.1 sec. (That is enough time to be able to distinguish between the noises made and the reflected sound.) CALCULATION 7

 By knowing the speed of sound and measuring the time it takes to hear the echo, you can calculate the distance of the object.  A sonar device sends out a sound and automatically calculates the distance of an object. Submarines use sonar to find objects under the water, including other submarines. When you hear the "ping" sound when in a submarine, that is the sonar sending out a sound wave under water. Fishermen also use sonar to find schools of fish. Since this is an electronic device, the time it takes for the wave to return can be much less than the 0.1 second required to hear an echo. USING ECHOES TO MEASURE DISTANCE 8

 For example, if the speed of sound in water is 1500 meters per second and the fisherman's sonar device detects an echo in 0.02 seconds, the distance of the object under water will be d = vt = 1500 meters per second * 0.02 seconds = 30 meters (back and forth).  That may mean a school of fish is 15 meters away. MEASURING DISTANCE 9

 Echolocation is a sensory system that involves using echoes to determine the direction and distance of an object and sometimes even the shape of an object. ECHOLOCATION 10

 Bats use echolocation to find their food and their way. With echolocation bats are able to tell the direction of an object, how far it is, how fast it is, and how big the object is by making sharp clicking and chirping sounds though their mouth and nose.  Dolphins-like bats, use short pulses and high frequencies using clicking and whistles, sent out of an opening below their blowhole. They use echolocation to find walls, other big sea animals and other dolphins.  Ben Underwood lost his sight at the age of 3. He is an expert in echolocation. As a result, he lives life as if he never went blind. ECHOLOCATION 11

ECHOLOCATION 12

What is an echo?  An echo is the reflection of a sound that bounces off an object and travels back to the sound source.  Echoes are used to measure distance, size and shape.  It is an important factor for bats and dolphins to survive.  Some blind people also depend on echoes to live life. SUMMARY 13