Sequence | Background | Objectives | Materials | Activity | Extensions | Evaluations

TOPIC-TITLE Deep Sea Technology - Seeing by Sound AUTHOR Gary DiCenso Paula McDonnel Virginia McIver GRADE SUITABILITY Middle School SCOPE Earth Science Biology Physics Mathematics

Sequence Before this activity students should understand how sound travels through different media. < < go top

Background Summary Underwater environments are often too distant and too dark to permit visual observation. Frequently oceanographers use SONAR (sound navigation and ranging), which depends on sound energy to provide pictures of the deep sea environment. SONAR sends sound waves through water, which bounce back to the source after they hit an object. Scientists can calculate how long it takes the sound wave to travel to and return from an object on the ocean floor. Therefore, they know how far the object is from the SONAR source. According to Greene (1998), the following formula is helpful in calculating ocean depth employing sonar: Depth (D) = 1,454 meters/second x time (t) /2 (note: 1,454 m are used because sound travels this distance per second, and the time is divided in half because the sound waves must travel to and return from an object). Researchers use this information to develop three-dimensional models of an object on the ocean floor. < < go top Objectives Students will able to do the following: Demonstrate understanding of SONAR. Determine the distance from an object by creating a model. Use the model to draw and label a diagram in an oceanic floor profile. < < go top Materials Overhead transparency of oceanic bottom features Books Graph paper Super balls Meter stick Stopwatch < < go top Activity Discuss sound waves and how they travel at different speeds in different media. Focus on how sound travels through seawater, and write the speed (1,454 meters per second) on the board. Use a transparency of the ocean floor demonstrating different forms beneath the surface: sea mounts, ridges, trenches, the continental shelf, the continental slope, and abyssal plains. The average depth of the ocean is 3,790 meters; however, the deepest trench is the Mariana Trench in the Pacific at 11,022 meters. Also, if possible, have students access the website at http://www.tritontech.com (steps to follow: cool links, Klein, then hot maritime group). This will provide visual images and additional background information. Divide the students into groups of four. Have them construct a random profile of the ocean floor in a straight line using stacks of books. Have each group prepare an observation chart and an oceanic profile chart. The data observation chart will include students' measurements in seconds every half meter. Students will use the oceanic profile chart in taking data from the observation chart and converting these data from seconds to meters (1,454 meters per second.) They will then plot the conversion to meters on the vertical (y axis) and the distance in half-meter intervals on the horizontal (x axis). Have one student release the super ball, stabilizing his wrist on the meter stick. A second student will hold the meter stick steady. The third student will time the release. The fourth student should be the recorder. Set the stopwatch and synchronize the release of the super ball over the first stack of books. Record the time from when the ball is released until it returns to the starting height. Repeat this three to five times and average the time. (Be sure the students understand the bouncing ball represents a sound wave bouncing off the ocean floor). Repeat the procedure every half-meter distance across the simulated oceanic floor profile, recording measurements. Have the group create a bar graph to represent the oceanic profile, labeling bottom forms as necessary. Provide each group an opportunity to present its respective graph in relationship to the simulated profile and those presented by other student groups. Include a discussion of possible ocean forms illustrated by the presented profiles. Explain how SONAR technology plays a part in animal adaptations, commercial fishing, and echoes. < < go top Possible Extension Investigate satellite imagery and compare to SONAR. On a field trip to a lake or quarry, where you can obtain an echo, use real sound travel formulas to calculate the length of the quarry or lake. Build a model of the ocean floor using the student oceanic bottom profiles. < < go top Teacher Evaluation After the simulated ocean floor has been cleared, have groups exchange graphs and reconstruct the oceanic profile indicated by the graph. Pre-and posttest, including questions such as these: Explain how dolphins locate objects in the ocean. If you were an oceanographer, describe two situations in which you would use SONAR and what information you would gain from its use. < < go top