Tuning Forks TEACHER NOTES. Sound Laboratory Investigation. Teaching Tips. Key Concept. Skills Focus. Time. Materials (per group)

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1 Laboratory Investigation TEACHER NOTES Tuning Forks Key Concept Sound is a disturbance that travels through a medium as a longitudinal wave. Skills Focus observing, inferring, predicting Time 40 minutes Materials (per group) 2 tuning forks, 320 Hz beaker, 400 ml water rubber band resonance box Teaching Tips The 320-Hz forks provide a good mid-range frequency. Forks of other frequencies will also work. To prevent accidental breakage, you can use plastic beakers. Make sure students fully describe their observations and record them in the data table. You could have several students listen from different distances from the activity to note any changes in sound. These students would record their observations and compare them with the other participants. Have students discuss what they heard in the different steps of the procedure and speculate on why they heard what they did.

2 Name Date Class Tuning Forks Pre-Lab Discussion If you could live in outer space, you d have a very quiet life. Why is that? The energy of a sound wave disturbs the molecules in a medium, making them rock back and forth in time with the wave frequency. When the disturbance reaches your ears, you hear sound. When the vibrations are very fast, you hear a high-pitched sound. When the vibrations are slow, the pitch is low. Sound can also travel through solids and liquids. The speed of the sound depends on the temperature, the elasticity, and the density of the medium. If there is no medium, as in the vacuum of outer space, there is no sound. In this investigation, you will use two tuning forks that vibrate at the same frequency. You will test how sound affects and is affected by different media, different speeds, and interference. 1. What does sound do to the surrounding medium? 2. What property of a sound wave changes as it gets louder? Problem How does sound interact with a medium? Materials (per group) 2 tuning forks, 320 Hz beaker, 400 ml water rubber band resonance box Safety Review the safety guidelines in Appendix A. Be careful when you strike the tuning forks against an object. Strike them against unbreakable objects (such as the heel of your shoe) and with just enough force to start them vibrating.

3 Name Date Class Tuning Forks (continued) Procedure Work with a partner. Take turns performing each of the six tests below and note any differences between your observations. Read through all six tests before you perform them. Always strike the tuning fork against the heel of your shoe. 1. Change of medium: Strike a tuning fork and insert the prongs into a beaker of water. Observe what happens. In the Data Table provided on the next page, record your observations. 2. Resonance A: Strike a tuning fork and bring it within a few centimeters of a second tuning fork with the same frequency. Bring the second tuning fork to within a few centimeters of your ear. Observe what happens. Record your observations. 3. Resonance B: Strike a tuning fork and note the loudness of the sound. Strike the tuning fork again and touch the base of its stem to the top of the resonance box. Note the loudness of the sound. Record your observations. 4. Interference A: Strike a tuning fork and bring one of the prongs to within 2 or 3 cm of your ear. Slowly rotate the tuning fork completely. Carefully note any change in the loudness of the sound. Record your observations. 5. Interference B: Fasten a rubber band securely on the middle of one prong of a tuning fork. See Figure 1. Using a second tuning fork of the same frequency, strike both forks. Touch the bases of the stems of the forks on the resonance box. If the sound is constant, reposition the rubber band and try again. Carefully note the sound emitted by the forks. Record your observations. 6. Moving sound source: Make sure you have plenty of room to swing your arm to the side. Strike a tuning fork extra hard. Rapidly move the tuning fork in a wide arc from your side to over your head. Note and record what you hear. Repeat this experiment with your partner standing several meters away. Does your partner observe any difference in sound at a greater distance? Record your observations and those of your partner.

4 Name Date Class Observations Data Table Test Loudness Change Pitch Change Description of Effect Analyze and Conclude 1. Did the loudness of the sound change in some tests? If so, give examples and explain why the loudness changed. 2. Why did the experiment include two tuning forks that vibrate at the same frequency? 3. How did the pitch change in the moving sound source test? Explain this observation.

5 Name Date Class Tuning Forks (continued) Critical Thinking and Applications 1. How does one vibrating object make another object vibrate, when they re not touching? What is true of both objects vibrations when this happens? 2. Why does sound get louder with the use of the resonance box? 3. The two tuning forks shown in Figure 1 have slightly different frequencies because there is a rubber band around a prong of one of the forks. How does this difference in frequencies explain what you heard in Step 5 of the procedure? More to Explore How might a change in the resonance box affect the sound that you heard from the resonance test? For example, what would happen to its resonance if the box were a different size or shape? What if it were filled with a gas other than air or a liquid medium? Choose one of the following variables: size of resonance box shape of resonance box substance within resonance box Write a procedure you would follow to test that variable. Include a hypothesis about how that variable affects the sound from the box. Have the teacher approve your procedure before you carry out the investigation.