Sound Waves

Sound Waves

• Sound waves are MECHANICAL WAVES.

• Sound waves are LONGITUDINAL WAVES.

• Sound waves are used in a variety of techniques in exploring for oil and minerals.

Sound Properties

• What does the loudness of the sound affect in the wave?

• What does the pitch affect in the wave?

• What is the difference between a smooth wave and a jagged “wave”?

Sound Properties

Sound Property Physical Wave Characteristic

Loudness Amplitude

Pitch Frequency

Quality Shape of wave

- Noise is jagged/not a smooth wave

Range of Hearing

What is this measured in???

What determines the speed of sound?

• The medium (mechanical waves need a medium)

Why is our voice distorted in water?

Speed of Sound in Air

• Sound waves are affected by the temperature.

• Formula: v = 331 + 0.59Tc

• Units: v is in m/s

• Tc is temperature of the substance in °C (which is actually not an SI unit!)

Example 1

• Suppose the room temperature was 22’C. Calculate the speed of sound in the classroom.

• Answer: v = 331 + 0.59 x 22

• v = 343.39 m/s = 340 m/s

Speed of Sound in Air

Example 2

Solution

Example 3

• The temperature is 4.0°C outside. If Mrs. Evans yells at her dog Pi to come inside and it takes Pi 0.015s to hear her, how far away is Pi?

• Answer: v = 331 + 0.59 x 4.0 = 333.36m/s• Assume the speed is constant!• v = d/t d = vt = 333.36 x 0.015 = 5.0 m• Pi is 5.0 m away!

Try These!

• Page 390, questions 1 to 6

• You may need to use the table on page 387!

Doppler Effect

• https://www.youtube.com/watch?v=z0EaoilzgGE

Doppler Effect

• The Doppler effect is observed whenever the source of waves is moving with respect to an observer.

• The Doppler effect: If the source of a wave is approaching you, the frequency will be higher.

• The actual frequency doesn’t change; we just “hear” that it changes because of our relative position. It appears this way because the source is moving closer (or the distance is decreasing between you and the source).

Doppler Effect

Doppler Effect

• https://www.youtube.com/watch?v=Kg9F5pN5tlI

• Video: http://www.bing.com/videos/search?q=doppler+effect&qpvt=doppler+effect&FORM=VDRE#view=detail&mid=9D8CCDECF5D691F025C79D8CCDECF5D691F025C7

• Discuss the “look” of each wave.

Doppler Effect

• What does this mean in terms of tone?

• As the object approaches you, the frequency will be higher, therefore higher tone/pitch.

• Vice versa: If you are in a position where the sound wave is moving away from you, what type of tone do you hear? Why?

• The Doppler Effect is how astronomists know that our universe is expanding. (PI video 3)

Check Your Learning – Sound Waves

1. The average human ear cannot hear frequencies above:

a) 20 Hzb) 2000 Hzc) 20000 Hzd) 200000 Hz

Answer: c)

Check Your Learning2. When the amplitude of a sound wave increases,

a) The wavelength of the sound decreasesb) The sound gets louderc) The pitch increasesd) The speed of sound increases

Answer: b

Check Your Learning3. Sound in a longitudinal wave because:

a) The oscillations in pressure are in the same direction that the wave moves.

b) The oscillations in pressure are perpendicular to the direction that the wave moves.

c) The wavelength is long compared to light waves.d) The wavelength is always longer than the amplitude.

Answer: a)

Check Your Learning4. The wavelength of a sound wave can be calculated bya) Multiplying the amplitude by the frequency.b) Dividing the amplitude by the frequency.c) Multiplying the speed by the frequency.d) Dividing the speed by the frequency.

Answer: d): the wave equation

Check Your Learning5. The speed of sound in air at 7.0’C is

a) 331 m/sb) 332 m/sc) 335 m/sd) 338 m/s

Answer: c) using v = 331 + 0.59T

6. A person is behind an ambulance as it moves away from her. The pitch of the sound that she hears is

a) Lower than if the ambulance was stationary.b) The same as if the ambulance was stationary.c) Higher than if the ambulance was stationary.

Answer: a)

Worksheet