Chapter 2

SoundSubject : Physics

Teacher : Piyanuch Plaon

Sound

Energy is transferred from particle to particle through matter.

How we hear?

Video about How we Hear?

How we hear?

a. Outer ear collects sound.b. Middle ear amplifies sound.c. Inner ear converts sound.

Longitudinal Wave (คลื่��นตามยาว)wave particles vibrate back and forth along the path that the wave travels.

Transverse waves (คลื่��นตามขวาง)wave particles vibrate in an up-and-down motion.

Parts of a Longitudinal

Wave

Compressions

Rarefactions

Rarefactions (ส่�วนขยาย) are regions of low air pressure Compressions (ส่�วนอั�ด) are regions of high air pressure

Compressions

Rarefactions

Sound Waves• Like other waves, a sound wave can be

described by its wavelength and frequency. • Wavelength is the distance from one

compression to another or one rarefaction to another.

• The frequency of a sound wave is the number of compressions or rarefactions that pass at a given point in one second.

Sound waves also reflect, refract, diffract, and interfere.

Propagation of sound

Medium (ต�วกลื่าง)- Material that sound waves can travel through.- It can travel through solids, liquids and gases but not through a vacuum.

The Speed of Sound• The speed of sound is usually fastest in

solids, where molecules are closest together, and slowest in gases, where molecules are farthest apart.

Speed of Sound

Depends on:1. Type of medium (ชน�ดขอังต�วกลื่าง)

- travels better through liquids and solids and gas can’t travel through a vacuum.

2. Temperature of medium (อั�ณหภู�ม�ขอังต�วกลื่าง)

- travels faster at higher temperature.

3. Density (ความหนาแน�น) - sound moves well through dense materials.

Video about relation between amplitude and

frequency

Intensity and loudness (ความเข�มเส่�ยง แลื่ะความด�ง)

1) Intensity depends on the energy in a sound wave.

2) Loudness is human perception of intensity.

3) Loudness is measured on the decibel scale.

Properties of sound

Amplitude and Energy

• Sound waves with greater amplitude carry more energy and sound louder.

• Sound waves with smaller amplitude carry less energy and sound quieter.

• The higher the amplitude of the wave is, the more compressed the particles in the compression are and the more spread out they are in the rarefactions.

Relation between amplitude and loudness

- High frequency means more vibrations hitting the ear.- Pitch is how high or how low a sound seems to be.- Healthy humans can hear from 20 Hz to 20,000 Hz- We are most sensitive from 440 Hz to 7,000 Hz.

Frequency and pitch

Relation between frequency and pitch

- Ultrasonic sound has a frequency greater than

20,000 Hz.

a) Dogs (up to 35,000 Hz) b) Bats (over 100,000 Hz)

- Infrasonic sound has a frequency below 20 Hz

Frequency and pitch (Con.)

Range of frequency