HPP Activity 49v1
What is the speed of sound?
Exploration
GE 1.
1. If you yell at someone across the room can they hear you instantaneously?
Explain your answer.
2. Get two boards and a stop watch. Go outside and pace off about 150
meters. Let one person slap the two boards together and let another person
stand 150 [m] away with the stopwatch and time the delay between seeing the
boards and hearing the sound. Estimate the speed of sound. )If you cannot go
outside then view the video clip, soundDelay560ftA.mov. The camera is 560
feet away from the source in this video.)
While you can experience a delay between sound production and hearing the sound in this
situation, it was probably difficult to make a precise measurement of the time delay. We will
explore this situation more precisely by using the computer to take the data.
Obtain
Long tube, ~1.5 [m] long
Microphone
MBL system with DataStudio
Close one end of the tube off with wood or stiff cardboard.
Set up the microphone at the open end of the tube and connect it to the MBL data collection
device.
Our goal in this exploration is to record the sound of your fingers snaping and then the echo of
the snap after it has traveled the length of the tube and back.
GE 2.
1. What data must you collect in this situation to measure the speed of sound
in the tube?
2. Start the data collection software and load the activity file
(SpeedOfSound.ds). Click the Start button and snap your fingers. Paste a
copy of the oscilloscope output here.
Activity Guide
 2010 The Humanized Physics Project
Supported in part by NSF-CCLI Program under grants DUE #00-88712 and DUE #00-88780
HPP Activity 49v1
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3. Using your collected data, calculate the speed of sound in the tube.
4. Repeat your measurement at least five times and calculate your best
estimate of the speed of sound (what property of the sample would this be?)
and the uncertainty in this estimate.
5. Suppose you could heat up the air in the tube. Do you think the speed of
sound would change?
Invention/Application
The speed of sound depends on properties of the medium. Generally it will depend on an elastic
property and an inertial property of the medium. We can expect that temperature will affect the
elastic property of the medium.
We will develop a mathematical model of how the speed of sound depends on temperature.
Since varying temperature of the air in a controlled fashion is difficult to do in our lab, we will
use a computer simulation to generate some data. Go to the Flash simulation "Speed of Sound"
in the course web. Note that you can simulate the experiment we just did, obtaining the
oscilloscope output for a sound and its echo. The time between producing the sound and hearing
the echo is obtained from the simulated oscilloscope, just as you did in the real experiment.
GE 3.
We will apply the XRAYS problem solving strategy to develop our
mathematical model.
1. eXploration: Using the Speed of Sound simulation, explore the relationship
between the temperature of the medium and the speed of sound in that
medium. Give a verbal description of the relationship here. Describe the data
used for this initial description.
2. Record: Record any given information that might possibly be important in
solving the problem. Record any information you will need to collect.
Include a figure that shows exactly what you are measuring.
Diagram:
Activity Guide
 2010 The Humanized Physics Project
HPP Activity 49v1
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Given and needed information:
3. Apply: Specify any physics concepts needed to analyze the data to help
yield a solution to our problem. Explain how you will use the concepts and
data to obtain a mathematical model relating sound speed to air temperature.
4. Yield: Obtain the data, do required calculations, as described above, and
present your mathematical model.
Data and Calculations:
Graph:
Equation:
Verbal Description:
5. Scrutinize: Are the speeds obtained from your calculations reasonable?
You might compare the room temperature simulation with the speed obtained
from the real experiment.
Activity Guide
 2010 The Humanized Physics Project