Physics 12: 1-9 Sound
Text Reading: Giancoli, Physics - Principles with Applications, Chapter 12: 1-9 (all)
- 12.1: When we talk about sound, we have two phenomena: the wave itself, and human ability to hear sound. So many of our measurements about sound relate to human interaction. Pitch, loudness, audible range all describe human hearing. The sound wave itself is a longitudinal wave, made of successive areas of compression and expansion of air.
- 12.2: Loudness is our experience of intensity, which in turn is related to the actual energy carried by the wave. Intensity is measured in decibel units: Β = 10 log I/I0.
- 12.3*: Air molecules move only 1.1 * 10-11 m in creating the highest note we can hear (around 1000Hz). Intensity and frequency together determine whether we can hear a sound.
- 12.4: Standing waves occur in three situations: on strings fixed at both ends; in pipes closed at both ends, and in pipes open at one end. For a standing wave to occur, there must be a node at a closed end and a maximum amplituded at an open end.
- 12.5*: Sound waves are additive; if a wave is sufficiently garbled, we hear it as noise.
- 12.6: Expanding wavefronts from two or more sources will interfer with each other. Where maxima add, we get beats.
- 12.7: The Doppler affect occurs when a wave source and the observer are moving relative to each other. Sound waves will appear to be longer (and lower in pitch) if the distance between a source and observer is increasing, and shorter (higher in pitch) if the distance is decreasing.
- 12.8*: If the source of a wave is traveling faster than the wave, the wave fronts become increasingly closer together, eventually "piling up" at the point of the object and creating a sonic boom.
- 12.9*: Because sound waves are generally non-destructive, sonar and ultrasound can be used to create images denser objects embedded in rarer medium, such as the ocean floor or bones in a baby still in utero.
Read the following weblecture before chat: Sound
clicking to run the simulation will download a Java file to your computer. If you have the appropriate Java library loaded, you will be able to run the simulation locally.
Use the simulation to explore how waves interact when you very frequency, amplitude, and number of speakers, and when you use a wall at different angles to reflect the sound.
Physics simulation Java Applets are the product of the PHET Interactive Simulations project at the University of Colorado, Boulder.
Chat Preparation Activities
- Forum question: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer before chat starts for this session.
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- Required: Complete the Mastery exercise with a passing score of 85% or better.
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