Measuring the Speed of Sound
Lesson 3 of 6
Objective: Students will measure the speed of sound in air using resonance tubes.
During the previous two lessons, students were introduced to the fundamental characteristics of sound and the Doppler Effect. The goal for today's lesson is to expand on our understanding of sound characteristics and investigate the speed of sound in the classroom (HS-PS4-1). Specifically, students use resonance tubes to compare the speed of sound in our classroom with the accepted value of 340m/s (SP3 - SP5). I start the class with an attention-grabbing video before moving into the actual lab activity. Today's lesson ends with an ABC summary.
This lab requires the following materials for each lab group: graduated cylinder filled with water, a resonance tube, a meter stick, and tuning forks.
As soon as students come into the room and are seated, I play this video to pique the students' interests about resonance tubes. The goal is to get students engaged by watching what they are about to do in the activity portion of today's lesson. The video provides students with a great example of what they should experience, along with a little humor and fun music. Because students are active for the majority of today's class, I don't worry much about this introductory strategy being passive.
The video describes harmonics, shows the equations to calculate harmonics, and then demonstrates the physical process of finding harmonics using a resonance tube. Because this video provides an example of what students do in the lab portion of today's class, it serves as a way to introduce students to the conceptual and quantitative concepts of harmonics (and the speed of sound).
Speed of Sound Lab
The goal of this lab is for students to apply their knowledge of sound waves and calculate the speed of sound in the classroom. At this point in the year my students have formed deep relationships with each other, so I allow them freedom in choosing lab partners. Groups of three seem to work best for the lab so one student can operate the resonance tube height, a second can activate the tuning fork, and a third student is able to record the data. After they've chosen their groups, someone from each group needs to get a copy of the lab and necessary materials.
Students start by taking a variety of measurements, including the temperature of the room and the inside diameter of the resonance tube. After they've recorded these initial data, students vibrate one of the tuning forks and move the resonance tube up until they reach a point of loud sound. At this location, students record the length of the tube that is above the water level and then repeat the process with different tuning forks. After recording the tube length for at least four different forks, students graph frequency vs. wavelength, and then draw conclusions about the relationship between frequency, wavelength, and the speed of sound in air.
The procedure in the lab document is straight-forward, but I still make sure to circulate throughout the room and check-in with the groups. I offer feedback on how students can start vibrating their tuning forks and raise the resonance tube. I also help students relate the lab activity to the harmonics equations discussed in the introductory video. At this point in the year, students understand the expectation that once they have completed collecting the data it's time to move into the data analysis section. As I walk around, I might ask student to "Tell me why the inside diameter of the tube is so important." Or "What sort of unit conversions do you need to make as you collect and record data?"
When there is approximately 10 minutes prior to the end of class (5 minutes left of the time I've allowed for this activity), I ask students to put everything back the way they found it and return to their seats. I also tell them at this point that the completed lab is due at the start of the next class meeting.
ABC Closure: Speed of Sound
In today's closure, students are each assigned a letter of the alphabet and must come up with a word that starts with that letter and pertains to the concepts covered in class today. After about thirty seconds of processing time, students share out their words with the rest of the class. I use this closure strategy when I want to do a basic check for understanding, and today students did a nice job of summarizing what was learned with their words. When I hear students contributing words such as "resonance" and "column" I see evidence of learning because those were words students needed to use to successfully complete the lab. Some of their responses were most certainly creative, such as "quantized" and "Young's Modulus", but I give them credit for at least having some fun with the activity and using physics vocabulary!