Sound Waves More Than Meets the Eye!!

What type of wave is this??? Transverse

How does this wave travel??? Perpendicular

What types of waves are Transverse??? Electromagnetic Visible Light Microwaves X-Rays

An Example…….

What type of wave is this??? Longitudinal Compressional

Parallel How does this wave travel???

Sound!! What type of wave is Longitudinal???

How sound works….

Waves are periodic, meaning they are disturbances of energy which repeat.

1 Cycle Successive identical parts of a wave is a cycle, or λ The time it takes for one cycle is a period or T

Frequency is cycles per second. f= 1 T

A wavelength ( λ ) is a cycle. λ is usually crest to crest.

A wavelength ( λ ) is a cycle. But λ can be any two successive identical points on a wave.

Sound is vibrations which create compressions in the air.

These compressions travel to our ear drums where we experience sound.

High frequency waves have a high pitch.

Low frequency waves have a low pitch.

This is best observed in the Doppler Effect.

When wave source is moving waves are high frequency in front of the object.

When wave source is moving waves are low frequency in behind the object.

A wave on a string moves faster the more tension the string has on it.

Just like compressions move through a slinky faster when the coils are tighter..

Remember….. v = λf or v = λν The frequency of a sound wave determines the pitch of the sound. High frequency = High pitch Low frequency = Low pitch The loudness of sound is determined by the amplitude. More amplitude (thicker compression) means louder sound.

Sound moves faster through warmer air because the molecules in warmer air are moving faster. Medium Speed of Sound Air at 0°C 331 m/s Air at 20°C 343 m/s

Sound moves faster through more dense matter and slower through less dense matter. Substance State Speed of Sound Oxygen at 20°CGas316 m/s Freshwater (20°C)Liquid1482 m/s CopperSolid5010 m/s Glass (Pyrex)Solid5640 m/s

Speed of sound in Various Media Medium m/s Air (0°)331 Air (20°)343 Helium (0°)972 Water (25°)1493 Seawater (25°)1533 Copper (25°)3560 Iron (25°)5130

Sound is measured in decibels (dB) Common Sound Approximate Decibels Threshold of hearing 0 dB Whisper20 dB Normal Talking65 dB Car without muffler 100 dB Loud Music120 dB Hurts Ears130 dB

Ultrasonic sounds are so high frequency we can’t hear them Bats can hear much higher frequency of sound, which they use as sonar.

Sonograms use ultrasonic sound to make images of developing fetuses.

Humans hear best at frequencies of 1,000 to 5,000 HZ.

Sonograms are done at up to 15,000,000 Hz !!!

Sound waves can be used to look at the heart as well.

Sound Waves and Music 1 st Harmonic 2nd Harmonic 3rd Harmonic 4th Harmonic 5th Harmonic 6th Harmonic

Sound Waves and Music At n = 1, λ = ½ At n = 2, λ = 1 or 2/2 At n = 3, λ = 2/3 At n = 4, λ = 2/4 or 1/2 At n = 5, λ = 2/5 L = length of string

Standing Waves are created in musical instruments.

We can look at compressions and rarefactions as crests and troughs..

And apply this to musical instruments….. In the first harmonic of an instrument closed at one end and open at the other ( a clarinet) the harmonic is ¼ of the total wavelength.

Saxophone is closed end.

And apply this to musical instruments….. Instruments with a closed end resonate at antinodes.

And apply this to musical instruments….. 4 λ

λ = 4L 4 λ L

λ = 4/3 L 4 λ L 3 Node

λ = 4/5 L 4 λ L 5 Node

Closed-Tube Harmonics Resonates at odd number quarter wavelengths

Flute is open pipe.

Open-Tube Harmonics Resonate an even number of quarter wavelengths.

Some wavelengths for open pipes. λ = 2L λ = L λ = 2/3 L

They are the same just at nodes or antinodes. λ = 2L λ = L λ = 2/3 L

Excellent Summary!!

The End