Students are shown a video of vocal chords generating sound, followed by a discussion about how vocal chords generate sound by vibrations, sound being a propagation of the vibrations through the air as a variation in air pressure, eventually causing the ear drums to vibrate. Students are then shown a demonstration with a slinky to visualize compressions and rarefactions. They also see a video of a spring moving by compression and expansion, to visualize compressions and rarefactions. Through a class discussion, the teacher graphs the air pressure variations along a sound wave as a function of distance on the board to show how it is a sinusoidal wave.
Students then do a lab using tuning forks, microphone and loggerpro software to graph the wave generated. Students calculate the amplitude, frequency, period. Students use a different tuning fork to see how pitch variations translate to frequency.
Students start with warmup questions to refresh frequency and period calculations from the previous lesson. Then they listen to a demonstration of how sound from two sources of almost identical frequencies generate beats that match the difference in the frequency.
Students then work in pairs explore the behavior of reflections on waves with a fixed end and loose end, with a PhET simulation. And students explore interference between the incident and reflected pulses using two pulses, and make inferences on constructing and destructive interference. Students watch three short videos that demonstrate the wave reflection with a real objects.
Students are shown a demonstration of standing waves using a spring. Students understand standing waves with the concept of constructive and destructive interference through a simulation on standing waves. This is extended to resonance by showing demonstrations of singing wine glass, a tube of air resonating with a tuning fork by changing the height of the air column above the water, and a singing tube that resonates at different harmonics when rotated in the air.
PhET simulation: Reflections: handout
Students warm up by participating in a quizlet game that reviews the concepts and vocabulary introduced so far.
Students then work through a lab to determine the speed of sound. The lab uses a "Direct Measurement" video from the Science Education Research Center (SERC) at Carlton College, where people standing in a line at different distances from a metronome clap when they hear the metronome. They clap at different times because of the time it takes for sound to propagate to each person. The interactive video at the SERC website allows advancing or rewinding frame by frame, allowing the students to capture the frame where any one person claps. The time between frames is 1/480 of a second, since the frame rate of the video is 480 FPS. The distance between each person is known, allowing the students to calculate the speed of sound as distance divided by the time.
Students discuss among themselves and propose a method to determine the speed of sound from the interactive video. The most common solution proposed is to determine the time it takes to reach the last person, and divide the distance by it. Another solution provided is to find the time when each person claps, and graph the distance versus time. The slope of the line will be the speed. Students are given the option of using the calculation method, or encouraged to use the graph method for extra credit. Students submit their notes from the lab handout to Google Classroom.
Students then predict in a whole class discussion if sound will travel faster in air or water. They then watch a video made by a UCLA professor on the speed of sound, with which they can check their prediction.
Students explore an Physics Classroom simulation, using which they can observe the relationship between frequency, wavelength and velocity of sound. This is followed by a whole class discussion through which the equation for the velocity of a wave in terms of its frequency and wavelength are established.
Students end the class with two practice problems, using which they apply the relationship for velocity of sound that they have learnt.
Keep in Time: Interactive Video
Speed of sound in different media: Video