# A disturbance in a medium that transfers energy and momentum

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A disturbance in a medium that transfers energy and momentum
Waves A disturbance in a medium that transfers energy and momentum

To produce a Wave: A vibration (disturbance)
A medium – a substance to travel through.

Examples of Waves Sound Light Water

There are two types of waves

Transverse – the individual wave particles move perpendicular to the velocity of the wave.
Examples: Electromagnetic waves (light waves, radio waves, microwaves, x-rays) Wave on a string

Longitudinal – the individual wave particles move parallel to the velocity of the wave.
Examples: Sound Waves

Parts of a wave: Frequency – The number of wave cycles in 1 second.
Wavelength Amplitude Frequency – The number of wave cycles in 1 second. Units 1/s = Hertz (Hz)

Wave Interference – The combination of two or more waves.
Constructive interference – Two waves combine to make a bigger wave. Destructive interference – Two waves combine to make a smaller wave.

wavelength = (velocity)(Period) wavelength (m)
Period (s) wavelength (m) frequency (hz)

The Wave Equation v = velocity of the wave (m/s) λ = wavelength (m)
f = frequency (1/s = Hz)

Example1: A sound wave has a frequency of 256 Hz
Example1: A sound wave has a frequency of 256 Hz. What is the wavelength? The speed of sound is 340m/s.

Example 2: A radio wave has a frequency of 96. 9MHz
Example 2: A radio wave has a frequency of 96.9MHz. What is the wavelength? The speed of light is 3.0 x 108 m/s.

Standing Waves on a String
The velocity of a wave on the string depends on the mass per length of the string and the tension in the string. v = velocity of the wave (m/s) FT= Tension in the string (N) m = mass of the string (kg) L = length of the string (m)

The fundamental frequency 1st Harmonic.

The fundamental frequency 2nd Harmonic.

The fundamental frequency 3rd Harmonic.

The fundamental frequency 4th Harmonic.

The fundamental frequency 5th Harmonic.

Summary fn=nf1 fn= nth harmonic n = 1, 2 ,3, …..
f1 =1st harmonic (fundamental frequency)

Conditions for interference
L2 L1 P δ = path difference = L2 – L1 Constructive Interference δ = 0, λ, 2λ, 3λ ……. δ = nλ n = 0, 1, 2, 3, … Destructive Interference δ = λ/2, 3λ/2, 5λ/2 ……. δ = (n+ ½)λ n = 0, 1, 2, 3, ….…

Sound Waves The speed of sound in air at room temperature is 340m/s.
The speed of sound increases with increasing temperature. The speed of sound in water is 1500m/s. The speed of sound in aluminum is 5100m/s.

Human Perception Physics frequency Pitch Intensity/Amplitude loudness

Pressure fluctuations in air due to a vibrating tuning fork.
Applet

Frequency range of the human ear.

Ultra Sound

Human Ear

Sound intensity and the decibel scale

Beats Beats occur when two sound waves have slightly different frequencies interfere with one another. The number of beats per second is called the beat frequency. The beat frequency is determined by subtracting the two frequencies.

Standing Sound Waves in a Tube
The wave travels at the speed of sound (340m/s) Open ends must have an antinode Closed ends must have a node. A pressure wave is set up in the tube. A tube open at both ends acts just like the string. A tube closed at one end only has odd harmonics.

Open Tube Just like the string

Closed Tube Odd Harmonics

Pushing someone on a swing. The Tacoma Narrows bridge.
Resonance occurs when the driving frequency matches the natural frequency, resulting in large amplitude vibrations. Here are some examples of resonance Pushing someone on a swing. The Tacoma Narrows bridge. Breaking a wine glass with a sound wave Earthquakes totally destroying some buildings and not damaging others.

The Doppler Effect is a change in frequency (pitch) due to the relative motion of the sound source and observer. As the sound and listener approach each other the frequency is higher. As the sound and listener move away from each other the frequency is lower. The Doppler effect also occurs with light producing the red and green shift of distant stars. Doppler radar is used to track weather systems

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