## Let's Measure the Speed of Sound

### Richard Angelini Sr.

#### Description

This is an outside the classroom experiment. The students experience in concrete terms an investigation of the speed of sound by measuring it. It blends scientific research with math skills and teaches sound scientific investigative techniques.

#### Objectives

The student knows that vibrations in materials set up wave disturbances that spread away from the source (e.g., sound and earthquake waves).

#### Materials

-1 Drum or large metal pot (for beating on)
-1 Drumstick or large wood spoon (for beating with)
-1 25 foot measuring tape
-1 Empty cereal box
-Some tape
-1 Watch with a second hand

#### Preparations

1. Cut cereal box into a rectangle
2. Find a large hard surface, (like a racket ball court) to bounce sound off with no noise for several 100’s of yards behind you. It may be a good idea to test the experiment before the class to make sure there will not be any noise pollution that could hamper your experiment.

#### Procedures

NOTE: Prior to the day of this lesson administer the pretest which is the same as the posttest. Use the results to determine any additional background information that students will need. Students who score 100 on the test will need enriching activities that support and extend the lesson plan.

Introduction:
HOOK: Ask the students, “How many students hear sound? But how many students hear the speed of sound? To hear the speed of sound, we will need a tool and a procedure.”

Procedure:
1. Form the cut cereal box into a funnel shape with the wide end approximately 6 inches and the narrow end approximately 1 inch in diameter. Attach tape to hold the shape.

2. Tell the students, “This is the tool we will need. It will amplify our hearing.” At this time share the criteria for taking notes (see the assessment.) Make sure students take paper and pencils. Proceed to your experiment location.

3. Tell the students, “Sound travels slowly compared to light. We cannot see sound travel and few can hear it travel.” Yell toward the reflective surface. Say: “The echo is sound bouncing off that surface just like a ball would bounce. If we threw a ball at that surface, it would go to the surface, hit it, and bounce back toward our location. It would take time for the ball to go to the surface and an equal amount of time for the ball to travel away from the surface and back to us. A ball is matter. Sound is energy, but it will behave in the same way. It will bounce back and the time toward the reflective surface and away from the reflective surface will be the same.”

4. Measure out about 400 meters, (420 yards, or 1,300 feet) and strike your drum. Tell the students, “Notice the echo? Now we are going to measure the echo. We will measure how much time it takes for the sound of the drum to go to the wall and back to our ears. We will do this by measuring how many times the sound will make the trip there and back in one minute. Then we will divide the number of times by 60 because there are 60 seconds in one minute.

5. Find a student to beat the drum. The student must have a good ear so he/she will hit the drum again at exactly the same time he/she hears the echo. The student may find it helpful to filter out unwanted sounds by holding the paper funnel to his or her ear. Another student should count the number of drumbeats in one minute. Have all students record the data in their notebooks.

6. After the one-minute experiment is complete, repeat several times and record results.

7. Average the results of several tries of the experiment.

8. Use the following formula to calculate the speed of sound.

# beats X the distance to the reflective object X 2 = distance traveled in one minute

distance traveled in one minute divided by 60 = distance sound in one second

9. Express the result as meters per second: m/s.

The speed of sound varies with the temperature of the air. At 59 degrees F it will travel 1,116 feet, (340 meters) per second. At 212 degrees F it will travel 1,268 feet, (386 meters) per second. Perhaps your class would like to test this statement by performing the experiment when it is very cold and when it is very warm and compare the difference in speed

#### Assessments

Formative: Give points for the method students design to record the data in their notebooks. All information should be accurate.
1 point for just writing down the results
2 points if they record the results in a chart that shows the results of each attempt of the experiment
3 points if they average the results
3 points if they include a drawing of the experiment
5 points if they include the math computations with an explanation of the meaning
Before giving the posttest, check the notebooks for understanding. It may be necessary to individually work with students who have not demonstrated understanding.
Summative: Pre and Post Test Students should have the opportunity to compare the pre and post tests in order to see how much knowledge was gained.