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 Teaching Physics Blog

## AP PhysicsTeaching waves with the iPad

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Learning Objectives
Students will be able to demonstrate their knowledge of wave terminology, the principle of superposition, and resonance using iPad apps.

Activity Type
These activities could be used as an introduction to the associated wave topics, or they could even be used as a form of assessment.

Assignment Details
• Each of the iPad apps below can be used by teachers or students to demonstrate physics principles related to wave motion, the principle of superposition, and resonance. For each app, a sample activity idea is provided. Each of the apps listed in this post are free educational apps available in the iTunes App Store.
• String: This app consists of a simple string running the length of the iPad. Much like the "Wave on a string" simulation from PhET, you can adjust the properties of the string to make a variety of pulse, oscillating, standing, or traveling waves.
• Make a wave activity: Students work as individuals or in groups to create types of waves specified by the instructor. They pause the screen to demonstrate to the instructor that they have successfully created the assigned wave type. For example, students could be asked to create: one fast and one slow traveling wave, a standing wave with two antinodes, or two pulse waves headed toward destructive interference.
• LU Wave Lab: This app acts as a virtual wave table with several different modes of operation. A simple touch on the screen can send a single 2D pulse wave in all directions or start a sinusoidal pulse oscillating.
• Characterizing interference patterns: Students use the "sinusoidal wave source" mode of the app to experiment with how the separation between two pulsing sources influences the shape of the interference pattern. Student should try a variety of source arrangements to determine a general rule that describes the shape of the interference pattern based on the placement of the sources. After discussing as a class, formalize the rule by writing it on the board. Then ask students to predict what an interference pattern would look like with three oscillating sources.
• Fourier Touch: This app provides a wonderful illustration of the principle of superposition and Fourier synthesis. Any touch on the screen produces a sinusoidal waveform and an associated sound. The exact location of the touch on the screen influences the frequency and amplitude of the waveform. Multiple simultaneous touches produce multiple waveforms - each of their own frequency and amplitude. The sum of all of these waveforms is shown in the center of the screen.
• Beat patterns demonstration: By selecting two waveforms that are very close in frequency, this app nicely demonstrates the beat pattern that emerges. The audio generated by the two waveforms will clearly illustrate the characteristic wah-wah of a beat. By making small changes to the frequencies of the two waveforms, you can convincingly show that the beat frequency is equal to the difference between the frequencies of the two waveforms.
Instructor's Notes
• Each of these activities could be modified for a one-to-one setting or a classroom with only a single iPad. If only one iPad is available, ask a student volunteer to come to the front of the room to use the app as a demonstration.
• In the LU Wave Lab, be sure that you modify the "mesh boundaries" setting to "MTC" to make sure that the waves don't bounce off of the walls of the simulation.
• For further analysis of sound waves include Fourier decomposition, you may consider using the free iPad apps: oScope Lite, Octave Lite, and Fourier Lite, which use the built-in microphone to analyze sounds by creating a frequency spectrum.