Purpose:

The purpose of this lab is to explore kinesthetically the effect of sound waves travelling through material and encountering objects. When the sound encounters an object it is reflected is predictable ways which allow us to interpret the data.

You will not need any particular equipment of this lab beyond your minds and creativity. We will probably use larger groups for this lab for clarity. Here's how we will use our bodies to illustrate the process of sound propagation and reflection:

• I) Process Description: A model is a way of describing how we think about a particular setting. One model for sound waves is a row of people moving together through the world (like the crest of an ocean wave or a row in a marching band). When this wave encounters an object each part (represented by the individuals in the row) reflects according to our reflection rule. In the context of ultrasound this reflected sound might return to the place where it started and be detected. The detector records both when (time) the sound returns and how much (how many people) sound returns. Use the model described above to illustrate the behavior of a sound wave in each of the following settings.

• II) Flat Wall at some distance: Imagine a flat wall at some distance away that your sound wave is moving directly towards. Illustrate the behavior of your sound wave reflecting off the wall and returning to the detector. Generate a loudness vrs time graph for this setting. Show how you would calculate the distance to the wall using your data.

• III) Small flat object in between: We will put a chair out to represent a small object that is closer than the back wall. The surface of the chair will be parallel to the back wall. Sketch a graph of the returning sound wave at the detector showing the "loudness" of the sound returning as a function of time. Label the important features of the graph. How does your graph change is the chair is placed in different positions?

• IV) Small flat tilted object: This is the same as the previous setting except that the chair will be tilted so the flat surface is not parallel to the back wall.Sketch a graph of the returning sound wave at the detector showing the "loudness" of the sound returning as a function of time. Label the important features of the graph.

• V) Round Object: This time the object will be round. Sketch a graph of the returning sound wave at the detector showing the "loudness" of the sound returning as a function of time. Label the important features of the graph.

• VI) Challenge: In your group decide where (close to the wall, far from the wall, left or right) you want to place a simple object (flat, round, triangular) and how it will affect the reflected sound. Illustrate this for another group who will generate a "loudness" vrs time graph and try to determine what shape your object is and where it is located. Your partner group can "resend" the wave up to 4 times to gather additional data (we will decide whether they can change the direction of the wave).

LAB DELIVERABLES (turn in):

Present your groups data from the challenge setting presented to you. Show graphs of the loudness of the reflected sound as a function of time for each of the "tests". Based on what you learned from other activities in the lab describe the possible shape and location of the object.

Then describe the challenge setting your group created and how your wave reflected from it. Was another group able to figure out the shape and location of your object?