Speed of Sound
Teacher Instructions
Background Information:
In this laboratory exercise the students will investigate the concept of velocity and apply it to the velocity of sound. In the first part the students measure their own velocity by determining the amount of time it takes for them to travel a measured distance. They learn how to calculate the velocity as
speed = distance traveled / time to travel that distance
They will find that they do not always travel at the same velocity. When they walk the velocity is less than when they run.
In the second part the students measure the velocity of sound by measuring the echoes produced in a tube. They will find that sound travels at about 1000 feet per second or 330 meters per second. By measuring the echoes in tubes of different lengths they will learn that the velocity of sound stays the same even though the times and distances change.
(Speed of sound = 331.4 m/s at 0›C and increases 0.6 m/s for each degree above zero.)
Questions to ask to introduce / reinforce an understanding of speed: What do you measure on the speedometer on your car? What does the Speed Limit 55 sign by the side of the road mean? 55 whats? Velocity and speed are names for the distance you can travel in a certain amount of time. Discuss - Velocity = distance traveled / time to travel the distance Units - miles per hour, kilometers per hour, feet per second, meters per second.
Introductory Activities:
Take the class out to a field. Measure a distance of 50 feet. Have each student run from the starting point to the 50 foot mark and return. So the student travels a total distance of 100 feet. Measure the time for the student to travel the distance and calculate the velocity. Have the students do this walking and running to see that they do not always move at the same velocity. (If time is limited this can be done in the classroom over a shorter measured distance with one student as a demonstrator.) Send a student outside some distance away (100 to 300 feet) and have her slap two boards together to make a loud noise. The students will notice the difference between the making of the sound and the hearing of the sound. This difference in time is small and difficult to measure. Set up the microphone and ULI or LabPro so that the students can see the computer display. Hold the microphone toward a solid wall. Clap your hands together. You should see on the computer display the loud sound from the clap and then a smaller sound from the echo from the wall. Discuss what an echo is and ask where the students have heard echoes.
Set-Up:
Exact setup is determined by individual groups. Insure different groups have tubes of different lengths so their results can be compared . As necessary suggest adjustments that will allow students to capture a good echo.
Procedures:
Exact procedures are determined by individual groups. Or you can use the suggested procedures in the student instructions. Students may have trouble obtaining good graphs. Suggest they use a short sound such as a hand clap, a finger snap or rapping to objects together.
Data / Observation:
Since the Big Question involves speed insure the students are including the data necessary to calculate speed. (distance and time)
Calculations:
Students should show their calculation of time. Students should show their calculation of speed.
Conclusions:
Students should conclude that sound does have a speed and it is measurable The students should determine a speed of sound.
Questions
- Give students the actual value for the speed of sound. (See Background Information) Discuss why their values may differ. Some students may have a value off by a factor of 2 because they did not consider that the sound traveled twice the length of the tube.
- Discuss the conclusions of the students.
- Discuss questions raised by the students.
- Assign students to find answers to questions raised.
- Have the students describe an object based on a graph previously produced.
- Below are some additional questions that can be assigned or discussed.
- What do you see on the computer graph when you clap your hands?
- What parts of the graph show the original sound of the clap?
- What parts of the graph show an echo? Is there more than one echo?
- What happens if you remove the closed end of the tube?
- What happens to the echoes if you closed the end of the tube with a sponge?
- Why do you think the echoes behave like that?
- How can you determine how far away a bolt of lightning is?
- How do bats and dolphins use sound to see?
- Why is it important to remember that you are measuring an echo?
- On the graph how did the echo look different from the original sound of the clicking?
Extensions:
- Try measuring the sound in different length tubes.
- Determine the length of a tube by measuring the time for the echo.
- Determine the distance to a wall or the ceiling using the equipment.
Notes:
- There are no unusual safety hazards with this experiment.
The Big Question:
Does sound have a speed and if so can it be measured?
Equipment / Materials:
- Computer
- ULI
- ULI Microphone
- Sound program
- Meter stick
- Large packing tube about 6 to 10 feet long. Close the tubes at one end by taping on a cap of thick cardboard.
Computer Set Up
- Connect the ULI to the computer (use the modem port) and connect the ULI to a power supply.
- Connect the Microphone to DIN 1 on the ULI.
- Turn on the ULI and the computer.
- Open the program Sound.
- Under the DISPLAY menu select ONE GRAPH.
- Under the COLLECT menu, SET the GAIN to HIGHEST.
- Change the time scale from 0 to 25 ms to 0 to 100 ms by clicking on the 25 at the bottom left and typing in 100
Set-Up
- Place the tube on a table.
- Cover one end of the tube with cardboard.
- Place the microphone at the other end of the tube.
Procedures:
- Press START on the computer. When you do this the computer will wait for a sound loud enough to start collecting data
- Make a sharp sound near the open end of the tube. This sound can be a clap or a finger snap or any very short distinct sound.
- Once the computer collects data, press STOP on the computer before making another loud sound.
- To measure the times at which the echoes appear on the graph, choose ANALYZE DATA A from the ANALYZE menu. Then use the mouse to point to the graph and read the time that the echo occurs. Record your data on your lab sheet.
Data / Observation:
Clearly record all your data on your lab sheet.
Calculations:
Show your calculation for speed.
Conclusions:
State your value for the speed of sound.
Student Instructions for LabPro
The Big Question:
Does sound have a speed and if so can it be measured?
Equipment / Materials:
- Computer
- LabPro
- Microphone sensor
- LoggerPro program
- Meter stick
- Large packing tube about 6 to 10 feet long. Close the tubes at one end by taping on a cap of thick cardboard.
Computer Set Up
- Connect the LabPro to the computer and to a power supply.
- Connect the Microphone to Channel 1 on the LabPro.
- Turn on the computer.
- Open the LoggerPro software.
- Under the Experiment menu choose Show Sensors and select the student force sensor in channel 1.
- Change the scaling on the x-axis so that time is measured for 100 milliseconds or 0.10 seconds.
- Under the Experiment menu choose Data Collection... and select the Triggering tab at the top right. Check the Enable Triggering box and click OK.
Set-Up
- Place the tube on a table.
- Cover one end of the tube with cardboard.
- Place the microphone at the other end of the tube.
Procedures:
- Press Collect on the computer. When you do this the computer will wait for a sound loud enough to start collecting data
- Make a sharp sound near the open end of the tube. This sound can be a clap or a finger snap or any very short distinct sound.
- Once the computer collects data, press Stop on the computer before making another loud sound.
- To measure the times at which the echoes appear on the graph, choose Examine from the Analyze menu. Then use the mouse to point to the graph and read the time that the echo occurs. Record your data on your lab sheet.
Data / Observation:
Clearly record all your data on your lab sheet.
Calculations:
Show your calculation for speed.
Conclusions:
State your value for the speed of sound.
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