DMS 150 Lab 1

Physics DMS150: Lab I
Speed of Sound

Part I: Speed of sound in Air
This portion of the lab is to be done outside in the west parking lot (light-rail park-and-ride) between Washington and Van Buren.

Step One:
Divide into two teams and go to the parking lots on the west side of campus.
Team one takes air horn
Team two takes stopwatch and air horn
Move apart as far as you can (note you will need to know the distance between teams).
Team 1 visually signals as they sound the air horn (cell phones also work).
Team 2 will start the stopwatch when they see the visual cue, and stop the stopwatch when they hear the air horn.

Record:
The distance from the listener to the source. 180m
The time recorded for the sound to travel from source to listener. 0.34 sec
Make at least three measurements.

Step two:
This time we will record the round-trip time elapsed.
Team one takes the air horn and stopwatch
Using the same distance between teams
Team one visually signals and starts the stopwatch as they sound the air horn.
Team two signals when they hear the air horn and sounds the second air horn.
Team one stops the stopwatch when they hear the second air horn.

Record:
The distance between teams. 180m
Total time for sound to travel from team one to team two and back to team one. 1.44sec
Make at least three measurements.
Using the distance equation from your textbook, calculate the speed of sound in the air.

What is the speed of sound in air ________________?
Distance/time = rate 360m/1.44 sec = 250 m/s

Part II: Speed of sound in tissue and fluids
This portion of the lab can be done in the ultrasound lab
Cut a piece of tissue mimicking material at least 1.5cm thick and place in a container of water.
Measure the depth of the water and the tissue mimicking material using an ultrasound machine. Record this as the thickness of the slab or water.

Using a linear array probe, take a picture of the tissue mimicking material and water.
Measure the depth of the water and the tissue mimicking material on the ultrasound image.
Enter the measurement for water here __3.77cm____ this is D1
Enter the measurement for the tissue mimicking material as measured in the water _1.88cm_ This is D2
Enter the measurement of the tissue mimicking material as measured through the material ____1.53_ This is D3

What speed of sound does the machine assume? __1540m/s___
How much does the measurement of the tissue mimicking material as measured in the water differ from the measurement of the tissue mimicking material as measured through the material itself? 1.88cm – 1.53cm = .35cm This is D4

Numbers needed to calculate the speed of sound in the tissue mimicking material.
Thickness of slab (2) = D2
Speed of sound in slab = VS
Assumed speed of sound = VA Use: 1540 m/s
Difference in depth = D4

The next section shows how to use this information to calculate the speed of sound in tissue mimicking material For the time interval “t”, the sound beam actual traveled:

t=D2/Vs
For the same time interval “t”, the machine calculated the sound beam to have traveled:
t=(D2-D3)/VA
Therefore:
t=(D2-D3)/VA= D2/Vs
Now you need to use algebra we can solve for t and then substitute to solve the equations for VS
VS=VA/(1-D3/D2 )
Using the above equation calculate the speed of sound in the tissue mimicking material.VS=1540m/s÷(1-(.35cm)/(1.88cm))
VS=1540m/s÷(1-.186)
VS=1540m/s÷.8138
VS=1892m/s



Part III: BONUS – Speed of Sound in Tissue Mimicking Material

Recalculate the speed of sound in the tissue mimicking material using the actual speed of sound in water. (Note: this requires that the machine measurements be adjusted before calculating the speed of sound in the material.)