Learning+Sequence+for+Sound+Waves

Introduction
Even though sound could be heard, sound waves can not be seen. Normally students can not accept easily what they can not prove. So, this learning sequence is designed to show that understanding the wave nature of sound is necessary to understand and use sound in a variety of ways.

Sound is one example of wave behavior. GSES related to wave behavior include:
 * PS3 (9-11)–10

Sound Concepts

 * 1) Phenomena of sound: reflection (echo), refraction, superposition
 * 2) Hearing is normally limited to frequencies between about 20 Hz and 20,000 Hz.
 * 3) Sound is a mechanical wave, i.e a wave propagating in a material medium. Sound can not travel in a vacuum.
 * 4) Longitudinal motion & Transverse motion (Sound is transmitted through gases, plasma, and liquids as longitudinal motion; Through solids, however, it can be transmitted as both longitudinal waves and transverse motion.
 * 5) The speed of sound in the air: v=(331+0.606*T), where v is measured in meters/sec and T is the temperature measured in YYYY. The speed of sound varies with temperature and medium. Sound waves travel faster in solids than in gases, which explains why soldiers in ancient times listened to the sound of approaching enemy forces by placing their ears to the ground.
 * 6) The average power per unit area is called the **intensity**. The intensity measures energy per unit time per unit area, and has SI units of watts per meters squared (W/m^2). Intensity is proportional to the square of both the amplitude and the frequency. Additionally, sound intensity is the product of the sound pressure and the particle velocity.
 * 7) The [|Decibel] scale, in which the measure of intensity, is a dimensionless quality with units of decibels (dB).
 * 8) Doppler Effect is the shift in frequency and wavelength of waves that results from a source moving with respect to the medium, receiver moving with respect to the medium, or even a moving medium.

An Activity Sequence - Investigating Sound
A. Standing sound waves Object: math \lambda=v \times T math 3. standing wave **Misconception:** standing wave is static without speed.
 * The activity before investigation/ Basic concepts:**
 * 1) node, antinode, wave length, amplitude, frequency, period, speed
 * 2) wave length = wave speed * period

=
Standing waves: all the different parts of the medium move together with the same time dependence. Stand waves are typically present when the ends of a string are fixed or otherwise Constrained.Traveling waves: energy is propagated in a definite direction and with a definite speed, such as hipping one end of a rope. ======

B. Ruben Tube **Misconception:** Sound is transmitted through gase as transverse motion. C. Energy density of sound is expressed as the sound intensity over the sound speed. Activity: The sound breaks the cup. There are several Youtube videos related to this. Here is a page full.

media type="custom" key="9569890" align="center"

D. Rubbing the edge of cup with different amount of water in it to produce the standing sound waves with different frequencies. A Tuning Fork Tuning Fork could produce the sound with fixed frequency. After collecting the sound by microphone, students could use computer to do the analysis on the sound wave, which includes the wave length, amplitude, frequency, period, speed.
 * Guided Investigation:**

B Produce Harmonic Waves Using computer to make sound with specific amplitudes and frequencies. This activity could provide direct outcomes. Students could learn when amplitude becomes bigger, the sound is louder; Frequency becomes bigger, the sound is sharper.

C Music (Decompose random sound waves) Students could collect the music to computer, then decompose the random waves as the superpostion of Harmonic waves. The results could be viewed like spectrum after Fourier transform. Superposition principle: Any wave could be expressed as the superposion of sinusoid waves/ Harmonic waves.

D Produce Music by computer (Composition) With inverse sequences as Investigation C, students could make their own music by combining the sound waves with different frequency and amplitude.

(I) they know tools; (Students learn the basic functions from investigation and could explore other functions themselves.) (II) they are interested in topic.
 * The activities after investigation/ Personal investigation:**
 * Students will investigate only if
 * Team work
 * Options
 * 1) How a speaker works? How a microphone works? Compare a microphone to a speaker.
 * 2) Interference (Beats)
 * 3) Music and noise


 * Share/ Public**