Sound and Sound Waves
Sound waves form one of our major sensory links to the world, so it is important to understand
their properties. Without sound, we would be unable to communicate by speech, hear music, or
know when someone has snuck up behind you.
Sound waves will fall into three different categories when covering different ranges of
frequencies.
Name
Infrasonic
Frequency Range (Hz)
Characteristics
0-20
Sonic (AKA Audio)
20- 20 000
Ultrasonic
20 000 +
Very low frequencies of sound
that the human ear can’t
detect, but you may feel the
rumbling of the waves
through your body
Normal range for human ears,
although not everyone
(especially the elderly) will
hear to the extremes of this
range
Beyond normal hearing for
humans, although some
animals (like dogs) hear part
ways into this range. Also
used in medicine (e.g.
ultrasounds)
Speed of Sound
The speed of sound in air actually depends on the temperature of the air. At zero degrees the
speed of sound through air has been experimentally found to be 331.4 m/s and this value
increases 0.606 m/s for every increase of 1oC.
𝑚
𝑚
𝑣 = 332 [ 𝑠 ] + (0.59 [ 𝑠 °𝐶]) 𝑇 [°C]
where T is the temperature in oC.
Remember that the speed of a wave is not only affected by the temperature but also the type of
media. The same can be said about sound. Waves travel more rapidly in certain solids and in
hotter gases than in cooler than cooler ones.
Measuring the Speed of Sound
We are going to perform this lab as a class and we are going outside to determine the speed of
sound. To perform this lab we are going to require two blocks of wood, a stopwatch, a
thermometer and a meter stick.
Before we begin, we need to designate one person in charge of clapping the blocks, another for
measuring temperature, 3 for measuring the distance from the wall, 3 timers and two people to
record all of the values.
Procedure (Group)- Temperature Method
1. Record the current temperature outside using the thermometer in Table A. Do this 3 times
(spacing the times out when you measure)
Procedure (Group)- Echo Method
2.
Have 3 students pace out what 10 meters is in the classroom. (# of steps for them)
3. Locate a high wall with a clear space of anywhere from 50m to 100m. Have 3 students for
measurements measure the distance. Take the average value of their 3 distances and use
that as the distance.
4. Now clap the blocks together and listen for the echo so that the time between the previous
clap and the echo is the same as the time between the echo and the next clap. In other
words, clap the blocks so that a regular rhythm is set up: clap…echo… clap
5. When you have achieved the correct timing start doing the trials. Have the person in charge
of the stop watch time the number of seconds required for 20 clap intervals and have
somebody else record this time. Remember when counting the number of claps to start with
zero.
6. Repeat step 4 five times to get an average time. This average time interval is equal to the
time taken for the sound to travel four times the distance between you and the wall.
7.
Gather all of the appropriate data from the person recording all of the values. Record in
Table B.
Procedure (Group)- Distance Method
1.
Have students who measure distances measure out the distance of one side of the field
to the other.
2. Have a volunteer do a dramatic clap.
3. Have a student timer start the timer when they see the hands of the clapper go together,
then stop it when they hear the sound. Do three trials, recording the results in Table C.
Name:____________________
Purpose:____________________________________________________________________________________________
______________________________________________________________________________________________________
Data Tables:
Trial #
Temperature
Velocity
1
2
3
Table A- Temperature Method
Average Speed of Sound: ______________
Trial #
Distance (m)
Time (s)
Velocity (m/s)
1
2
3
4
Table B- Echo Method
Average Speed of Sound:________________
Trial #
Distance
1
2
3
Table C- Distance Method
Average Speed of Sound:________________
Time
Velocity
Analysis
1. Using the average speed of sound found from the Temperature Method, how does the
value of the speed of sound calculated experimentally compare to the one that you
calculated from the equation (theoretical value)? What was your percentage error? (do
for the Echo method and the distance method) (remember: % 𝑒𝑟𝑟𝑜𝑟 =
|𝑇ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑉𝑎𝑙𝑢𝑒−𝐸𝑥𝑝𝑒𝑟𝑖𝑚𝑒𝑛𝑡𝑎𝑙 𝑉𝑎𝑙𝑢𝑒|
×
|𝑇ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑉𝑎𝑙𝑢𝑒|
100%)
2. Account for the sources of error in this investigation and explain how they may affect the
results.
3. Knowing the speed of sound, how might you determine the distance between your point
of observation and a granite cliff some distance away?