SEAFLOOR PROFILING—Lesson #2: Echolocation



“SEAFLOOR PROFILING—Lesson #2: Echolocation,” student handout

ping pong ball



Procedure/Assessment for Lesson #2:

(1) It is suggested that you begin this lesson by reviewing “LESSON #1: SEAFLOOR PROFILING: introduction.” After the review, ask the students if they can think of situations when the seafloor mapping method they have learned would not work. Encourage all contributions; discuss. The idea to use for beginning this lesson is the idea that most parts of the ocean are way too deep to use a rope; the average depth of the ocean is 4000 meters, or over 12,000 feet! Therefore, to map most of the seafloor, an invention had to occur; that invention was echolocation.


(2) During World War I scientists found that sound waves could be sent from a ship, travel through the water, bounce off a hard object, and return to a sound recorder on the ship, in much the same way as light waves can be reflected from a mirror. A similar example is seen in some valleys or gorges where a person can shout across the valley and have his/her echo come back. For this reason, the scientists gave the name “echolocation” to the process of sound waves bouncing off hard objects underwater.


(3) During the War this application was used to locate enemy submarines. Harold Hess, a Navy officer during the War, later became an oceanographer and applied this technique to mapping the seafloor. By timing how long the sound waves took to go from the ship, down to the seafloor, and back again, he could calculate how deep the seafloor was. The deeper the ocean, the longer it took the sound to return to the ship. A rope was no longer needed; “sounding” could use real sound waves!


(4) In this lesson, the teacher will demonstrate the process of echolocation using a ping pong ball. The time needed will be a portion of a class period.


(5) Ask for a student volunteer to help you by using the stopwatch.


(6) Explain to the students that the ping pong ball represents a sound wave leaving the ship (teacher’s hand). The teacher should drop the ping pong ball from about 1’ above the floor, and catch it at the highest point of its bounce back up.


(7) The student timer starts and stops the watch to record the time it takes for the ball to travel the round-trip from the teacher’s hand, to the floor, and back to the teacher’s hand. Write this time on the front chalk/white board, using a red* marker, if possible.


(8) Repeat step #5 two more times, then calculate an average. This average represents the depth of a shallow seafloor.


(9) Repeat steps 7 & 8 a total of three times from a much higher elevation; perhaps the teacher should stand on a counter/desktop! Record these 3 trials using a blue or purple* marker. The second average represents the depth of a deeper seafloor.


(10) *These colors are the ones used by some professional scientists to show different depths; see Lesson #3 in this series.


(11) Have each student complete the “SEAFLOOR PROFILING—Lesson #2: Echolocation” student handout.