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In this lesson, students learn about echolocation: what it is and how engineers use it to "see" things in the dark, or deep underwater. Also, they learn how animals use echolocation to catch their dinner and travel the ocean waters and skies without running into things.

Obviously, we need to know where things are in order to function. And, many times we need to be able to "see" something even when it is dark outside or something is far away and obstructed, by the ocean or clouds, for example. Engineers have learned from nature how to use sound and radio waves to locate objects. This technology is called SONAR (SOund wave Navigation And Ranging) and RADAR (RADio wave navigation And Ranging). longitudinal waves sound waves echo echolocation sonar radar Longitudinal and Transverse Waves (Lesson 1), Wavelength and Amplitude (Lesson 2), Frequency (Lesson 3). After this lesson, students should be able to: Explain the basics of echolocation. Give an example of an echolocation application. After waiting out the storm, Angie and Harmon head back out to sea with Fisherman Frank to look for what they think is the wreck of a Spanish treasure galleon on the ocean floor. As they get farther from shore it gets increasingly difficult to see the ocean bottom, and they still haven't seen the galleon. How are they going to find the galleon now? Let's pretend that we are engineers, and we need to design a way for Angie and Harmon to see the galleon as it lies on the bottom of the ocean. Hmmm… what could we possibly do? Take a couple minutes to talk to the person next to you and see what engineering solution you can think up! (Ask students to share their ideas after about two minutes). Those are some fabulous suggestions. Many of your ideas involved different ways of seeing underwater. Animals that live in the water also have the problem of seeing underwater. In fact, many of them have eyes to see reflected light, but this only works to a certain depth until it gets too dark. Some animals have another way to see — they use sound waves instead of light waves. This is called echolocation. Echolocation is a big word, so I'm going to write it on the board. Any ideas about what it means? Well, we know what "location" means — it is where something or someone is located, right? What does "echo" mean? Have you ever heard an echo? It sounds like the sound, or noise, is bouncing back to you, doesn't it? Well, that really is exactly what's happening! The sound waves are bouncing off of something and coming back to you, so you can hear them again. So, "echo" has to do with sound waves bouncing back, and "location" has to do with where something is. Any ideas then about what "echolocation" means? What does it mean when we combine those two words? Why don't we take another minute and talk to the person next to us to see if we can figure it out. (Ask students to share their ideas after about one minute). Fabulous! Echolocation means using sound waves bouncing back to tell how far away something is. Many different animals — including bats, whales and dolphins — use echolocation to determine where they are in the dark or under water. It also helps them capture their dinner! Bats make very high-pitched noises, while dolphins make little clicking noises. The noises the animals make bounce off of objects and come back to their ears. The reflected noise, or the echo, will sound different depending on where the object is. These animals can tell how far away the objects are by listening to the echoes coming back. Engineers have figured out a way to do the same thing that animals do; however, they need some special equipment to do it. Engineers use sonar, which stands for Sound wave Navigation And Ranging. This technology uses sound waves to navigate ocean waters and skies. Radar, RAdio wave navigation And Ranging, uses the same principals, but with radio waves instead of sound waves. Sonar and radar work almost exactly the same way that echolocation for animals. This is a great example of how engineers mimic what occurs in nature and use it to help people who have needs similar to the animals'. You know about echolocation now, but first we need to talk a little bit more about sound waves. You have already learned about longitudinal and transverse waves, wavelength, amplitude and frequency. Sound waves have all these characteristics. When something or someone makes a sound, the sound creates pressure changes in the air (or water, if the sound is traveling through water). Those pressure changes travel to our ear, and our ear interprets them as sound. Now we're going to do a fun activity where you will get to see how good your echolocation skills are! Sonar is a system that locates objects by transmitting sound waves and detecting the waves when they are reflected off of objects. Bats and many other animals, such as whales and dolphins, use natural sonar to navigate and capture prey (also called echolocation). Bats emit high frequency noises, about 100,000 Hz (higher than the top range of human hearing, which is about 20,000 Hz), which echo off objects and then return to the bat's ears. Depending on how long it takes the sound wave to echo back to the bat's ears and from which direction it comes from, a bat can tell the location and size of the object. Dolphins and whales use echolocation to see underwater. They make clicking sounds that echo back to them and tell them where objects are located. Sonar signals are so precise they can create detailed sound "pictures" of objects. Animals that use natural sonar are able to get a very detailed "image" of where objects are located and how fast they are traveling. That's why bats are able to capture insects so successfully in mid-flight. Engineers used the concept of echolocation to develop SONAR (SOund wave Navigation And Ranging). SONAR works basically the same way as natural echolocation and is used in a wide variety of applications. Active sonar uses transmitters and receivers to send out and receive pulses of sounds. Based on the time it takes for the sound to reflect off an object and reach a given receiver, sonar operators can calculate how far away objects are located. Passive sonar does not send out signals, but only listens for signals generated by other objects. RADAR (RAdio wave navigation And Ranging) applies the same concept as SONAR except that it uses radio waves instead of sound waves. Figure 2 shows an actual SONAR image of a sunken ship. Two important components of understanding echolocation are to know (or at least become familiar with) what a sound wave is and what an echo is. A sound wave is a series of traveling density fluctuations in a medium (e.g., air or water) that our ear changes into a perception of sound. These density oscillations correspond to pressure fluctuations, where regions of greater density have higher pressure and vice-versa. A vibrating object in the air or water creates these density and pressure fluctuations. As mentioned before, our ears change the pressure fluctuations into our perception of sound. In other words, the greater the amplitude of the pressure fluctuation, then the greater will be our perception of the volume of the sound. We hear an echo when a sound wave bounces off another surface and returns to our ear again after a period of time. The sound wave can bounce again and again off of multiple surfaces, so it is possible to hear multiple echoes from a single sound source. A longitudinal wave that is made of a series of traveling density fluctuations in a medium (e.g., air or water) that our ear changes into a perception of sound. When a sound wave that we have already heard bounces off another surface and returns to our ear again after a period of time. Using sound waves to "see" the location of something. Some animals, such as bats and dolphins, emit sounds that bounce off objects and then echo back to their ears. From the direction and time it takes for the echo to come back, these animals can determine the location and distance of the object. Echolocation in Action! In our last lesson, we learned about frequency, and how sounds with different frequencies sound differently. In this lesson, we discovered how engineers can use sound to see things — even deep underwater. Pretty cool, isn't it! Who can remember the special word for "using sound to see"? Terrific! Echolocation is right! That is what many animals use to survive in their natural habitats. When engineers use echolocation, we have another word for it — who would like to say the word? Yes, SONAR. In our next lesson, we learn more about sound and how it can be absorbed by different materials. Angie and Harmon and Fisherman Frank are going to try to use the SONAR to find the sunken galleon… will they succeed or run into some problems? You will have to wait until our next lesson to find out what happens! Brainstorming: As a class, have the students engage in open discussion. Remind students that in brainstorming, no idea or suggestion is "silly." All ideas should be respectfully heard. Take an uncritical position, encourage wild ideas and discourage criticism of ideas. Have them raise their hands to respond. Write their ideas on the board. Ask the students: "What are some methods we use to tell where we are?" (Possible answers could include: maps, street signs, asking for directions, we know because we've been here before, we see familiar things, our family tells us where we are, a compass, the compass in our car, signs on buildings, signs on walls, etc.). Voting: Ask the following true/false question, and have students vote by holding thumbs up for true and thumbs down for false. Count the votes and write the totals on the board. Discuss the correct answer with students. People can hear the same sounds animals can. (FALSE. We can hear some of the sounds animals can, but some animals can hear a much wider range of sounds than humans.) Some animals use sound to "see." (TRUE) An echo is when a sound bounces off of something and comes back to our ears. (TRUE) Echolocation means using reflected sound waves to determine location. (TRUE) Sonar is the name of a spaceship. (FALSE. Sonar, which is short SOund wave Navigation And Ranging, is another word for echolocation. It is the type of echolocation that engineers designed to help people "see" in the dark or underwater.) One and Done: Ask the students to think of a situation where echolocation could help find something. Ask them to raise their hands when they have an example in mind. Call on students at random to explain their answer. Allow no repeat answers. (Possible answers: using dolphins to find mines underwater, bats using high-pitched noises to navigate, engineers using SONAR and RADAR for many applications, etc.) As a class or in small groups, watch a nature video on bats or dolphins to learn more about echolocation. Have student teams research different animals and the ranges of sounds that they can hear and make. To learn more about sound waves, show students the following animations: http://gbs.glenbrook.k12.il.us/Academics/gbssci/phys/mmedia/waves/tfl.html and http://www.kettering.edu/~drussell/Demos/waves/wavemotion.html. Henderson, Tom. Glenbrook South High School, Multimedia Physics Studio, "Longitudinal Waves and Tuning Forks," August 11, 1998, accessed February 8, 2007. http://gbs.glenbrook.k12.il.us/Academics/gbssci/phys/mmedia/waves/tfl.html National Aeronautics and Space Administration, Jet Propulsion Laboratory, California Institute of Technology, accessed February 8, 2007. http://www.jpl.nasa.gov/history/innovations/1983_sunken_ship.htm Russel, Dan, 1999. Ketterling University Applied Physics, Acoustics and Vibration Animations, accessed February 8, 2007. http://www.gmi.edu/~drussell/Demos.html U.S. Department of State, Secretary for Public Diplomacy and Public Affairs, Bureau of Public Affairs, Electronic Information and Publications Office, Photo Gallery, Photos by Regions and Topics, Near East: Iraq - 2003, March, "Dolphin Trained to Help Clear Mines Leaps in Water," http://www.state.gov/r/pa/ei/pix/b/nea/iraq/19132.htm Uy, Christine. Harvard Undergraduate Society for Neuroscience, "Seeing" Sounds: Echolocation by Blind Humans," 1994, accessed February 8, 2007. http://www.hcs.harvard.edu/~hsmbb/BRAIN/vol1/echo.html The Wild Ones, "Echolocation," 2000, accessed February 8, 2007. http://www.thewildones.org/Animals/echolocation.html Wikimedia Foundation. Wikipedia, "Animal echolocation," January 30, 2007, accessed February 8, 2007. http://en.wikipedia.org/wiki/Animal_echolocation Wikimedia Foundation. Wikipedia, "Sonar," February 6, 2007, accessed February 8, 2007. http://en.wikipedia.org/wiki/Sonar