Music, Math, and Motion

Dr. E.J. ZitaThe Evergreen St. College

Winter week 6

Friday 13 Feb. 2009

Ch.12: Intro to SOUND

• Where to find solutions to HW online

• Overview of 12a: § 1, 2, 3

• Discuss sections• Practice problems together

• Choose homework together, due next Friday

• Looking ahead

Giancoli solutions on Moodle

Overview of Ch.12.1: Characteristics of Sound

( )

20 ( )sound wavesin air

longitudinal

Elastic restoring force Air pressure Pspeed Temp Kelvin

Inertia air density n

You already know sound = longitudinal PRESSURE waves

and that the speed of sound depends on its medium.

using PV = nKT (ideal gas law). The result can also be expressed as

v ~ (331 + 0.60 T ) m/s (where temperature T is in Kelvin)

Overview of Ch 12.2: Intensity of Sound: Decibels

Intensity = I = Power / Area of sound wave (in W/m2)

Loudness = = perceived sound level (in decibels)

Basic tutorial in logarithms:In general, if mx = y ↔ logm y = x, or, in wordsIf m to the x power = y, then the (log of y to the base

m) = x.For example, log base 10, or common logs:

10x = y ↔ log10 y = x100 = 1 ↔ log10 1 = 0101 = 10 ↔ log10 10 = 1102 = 100 ↔ log10 102 = 2

Overview of 12.3: The Ear and its Response: Loudness

Sound (pressure waves) channeled down ear canal tympanum

(eardrum) vibrates middle ear transfers and amplifies signal (x 40) to

“oval window” in cochlea, which transforms vibrational energy to

electrical energy to brain. Sensitivity varies with frequency.

Jigsaw learning-through-discussion

1. Count off by 1, 2, 3• Each team discuss your section• Identify key points• Zita will circulate, answering questions

2. Mix teams so there is one expert for each chapter on each team

• Discuss all sections – share your key points

3. Whole group gather: resolve questions, share insights and examples, and choose homework together

Let’s try some HW together – you choose which

HW Ch.12. 2

HW Ch.12.3

General Problems Ch.12.1-3

Looking aheadTODAY