Wave Energy Transfer & Sound Wave Energy

If a vibrational disturbance occurs, energy travels out in all directions from the vibrational source. Ripple demo

All points on a wave that are in phase comprise a wave front.

Wavefronts join points in phase.

Rays – a ray is an arrow sketched through the wave fronts (perpendicular) to show direction of wave propagation.

Rays

Waves transfer energy Rate of E transfer is proportional to the A. Less energy More energy

For light increased amplitude increases brightness.

For sound: increased amplitude increases volume.

What does wave frequency ( f ) determine? Wave type for EM waves. Color for light. Pitch for sound

Hear different frequencies ds.htmlhttp:// ds.html Sound

Sound is a Mechanical Longitudinal/Compressional Wave

solid liquid gas In gas hot faster. cold slower. Increasing velocity Sound velocity

The Doppler Effect Stationary Source Emitting Waves all Directions. Circular wavefronts have = & f.

Doppler Effect from Moving Source In front of source is less, behind is longer.

In front of source -short higher f: hear higher pitch sound- see shorter light (blue). behind source - longer lower f: hear lower pitch sound see longer light (red).

When objects are in relative motion: a) Toward each other, f received increases. b) Away from each other, f received decreases. Doppler Effect

Doppler Clip 3.1 minutes pN5tlIhttp:// pN5tlI BYrbCjYhttps:// BYrbCjY

Resonance & Sympathetic Vibration

* Fact * All objects have a natural frequency of vibration. Resonance - the inducing of vibrations of a natural rate by a vibrating source having the same frequency “sympathetic vibrations”

Push at natural frequency, amplitude increases

Resonance: An oscillatory system that is driven by a force with a f = to its natural f. System will resonate – amplitude will increase. The natural frequency of objects is the frequency that produces a standing wave in the object. Can occur from reflection causing a standing wave. Amplitude is increased.

Sympathetic Vibration when a wave is near an object & is vibrating at the natural frequency of the object. Object vibrates sympathetically at same frequency – they resonate. Causes the amplitude to increase.

Break the glass 20 sec. 17tqXgvCN0E

Standing Waves on Guitar String ½.

hwk Rd Text 13 – 1 and 13-2 Wksht Review concepts sound.

hwk Rd 13 – 1 & pg 491 – 493 p.507 #1, 3, 6-8, 11-13, 15, 16

The three components of sound are: Pitch (how high or low) Loudness (volume) Timbre (tone color)

Pitch Vibration patterns are also called waveforms. Each repetition of a waveform is called a cycle. We can hear frequencies between 20 hertz to 20 kHz i.e. 20,000 Hz.

When the frequency of a sound doubles we say that the pitch goes up an octave. We can hear a range of pitches of about ten octaves. Many animals can make sounds and hear frequencies that are beyond what we can hear.

Loudness To create vibration energy is used. The greater amount of energy used the louder the sound. The strength of the changes in air pressure made by the vibrating object determines loudness.

As the distance from the source increases the amount of power is spread over a greater area. The amount of power per square meter is called the intensity of the sound.

Humans do not perceive sound intensity linearly. For us to perceive a sound as twice as loud its intensity must be ten times greater. The perceived intensity level of sound is measured in a logarithmic scale using a unit called the decibel (dB).

The scale begins (0 dB) on the softest sound that a person can hear. This is called the threshold of hearing. The scale ends at the volume that causes pain (120 dB) and is therefore called the threshold of pain.

Tacoma Narrows Bridge

mechanical universe resonance

“Timbre” (TAM-ber) or tone color is the specific property of sound that enables us to determine the difference between a piano and a harp.

A broad variety of tone colors exist because most sounds we perceive as pitch contain many frequencies. The predominant pitch is called the fundamental frequency. It is the longest that forms a standing wave.The predominant pitch is called the fundamental frequency. It is the longest that forms a standing wave.

Standing Wave patterns form notes. Each string or pipe vibrates with particular frequencies of standing waves. Other frequencies tend to die out.

Although we would perceive a string vibrating as a whole, it vibrates in a pattern that appears erratic producing many different overtone pitches. What results are particular tone colors or timbres of instruments and voices.

Waveform with overtones.

Frequencies which occur along with the primary note are called the harmonic or overtone series. When C is the fundamental the pitches below represent its first 15 overtones.

There are several standing waves which can be produced by vibrations on a string, or rope. Each pattern corresponds to vibrations which occur at a particular frequency and is known as a harmonic. Harmonics

The lowest possible frequency at which a string could vibrate to form a standing wave pattern is known as the fundamental frequency or the first harmonic.

2 nd Harmonic

Which One??

String Length L, & Harmonics Standing waves can form on a string of length L, when the can = ½ L, or 2/2 L, or 3/2L etc. Standing waves are the overtones or harmonics. L = n n. n = 1, 2, 3, 4 harmonics. 2

Harmonic Frequencies form where ½ can fit the string exactly. To calculate f: Substitute v/f for.

1 st standing wave forms when = 2L First harmonic frequency is when n = 1 as below. When n = 1 f is fundamental frequency or 1 st harmonic.

For second harmonic n = 2. f 2 = v/L Other standing waves with smaller wavelengths form other frequencies that ring out along with the fundamental.

In general, The harmonic frequencies can be found where n = 1,2,3… and n corresponds to the harmonic. v is the velocity of the wave on the string. L is the string length.

It is helpful to note that the distance between nodes on a standing wave is ½. ½

Pipes and Air Columns

A resonant air column is simply a standing longitudinal wave system, much like standing waves on a string. closed-pipe resonator tube in which one end is open tube in which one end is open and the other end is closed open-pipe resonator tube in which both ends are open

Open Pipe – open end has antinode.

Standing Waves in Open Pipe Both ends must be antinodes. How much of the wavelength is the fundamental?

The 1 st harmonic or fundamental can fit ½ into the tube. Just like the string L = n 2 f n =nv 2L Where n, the harmonic is an integer.

Closed pipes must have a node at closed end and an antinode at the open end. How many wavelengths??

Here is the next harmonic. How many ’s?

There are only odd harmonics possible. L = 1/4. L = 3/4. L = 5/4  f n = nv where n = 1,3,5 … 4L

Beats – caused by constructive & destructive interference from 2 frequency sounds interacting. Beat Frequency heard is the difference between 2 frequencies. If a 50 Hz wave and a 60 Hz wave overlap, you hear beat of 10 Hz.

hear beat frequencies

Traveling Waves Beats

Holt read pg 499 #1 – 4 Start in class finish for hwk.

Hwk read 491 – 503 do 499 and 503