Waves A “wiggle” or “oscillation” or “vibration” produces a Wave

Types of Waves Mechanical Waves Examples: water, rope, sound, slinky Requires a material through which to travel- a “material medium”

Electromagnetic Waves Examples: x-rays, UV, light, radio They can travel through empty space- a vacuum- they don’t require a material medium. In a vacuum, they all travel at the same speed— The “speed of light” This speed is constant and is called “c”. c = 3 x 10 8 m/s

Wave Motion Transverse Waves The wave disturbance is PERPENDICULAR to the direction of the wave’s velocity. “Crest”, the peak of the wave “Trough”, the valley of the wave “Equilibrium” line

Longitudinal Wave (compression wave) The wave disturbance is PARALLEL to the direction of the wave’s velocity.

How does this motion make a “wave”??wave

I. Sound is a longitudinal wave. * A.Molecules move parallel to the direction of the waves velocity. B.Areas of high pressure and low pressure C.“compression” and “rarefaction”

Wave pulse- one disturbance Traveling wave- repeated disturbances

Polarized waves If there are many waves and ALL the waves are vibrating in the same plane, they are said to be “polarized”

Measurements Wavelength, Wavelength, Distance between points where the wave pattern repeats- meters

Amplitude, A Maximum distance above or below equilibrium- meters

Period, T Shortest time interval during which the pattern repeats--- seconds Frequency, f The number of waves per second-- Hz f = 1 / T and T = 1 / f Velocity, v Distance / time = /T So… v = /T but also v = f

Water Wave “Surface” waves are combinations of transverse and longitudinal waves.

Waves transmit energy without transmitting matter. energy Most waves move through a substance but only move it backwards and forwards (longitudinal) or up and down (transverse) while the wave passes. After the wave has gone, the substance is back where it started but energy has been carried by the wave from its origin (where it begins) to its destination (where it finishes). longitudinaltransverselongitudinaltransverse

Behavior of All Waves Reflect : To bounce back from a surface Law of Reflection: The angle of reflection is equal to the angle of incidence.

Refraction : The change in direction as a wave passes from one medium into another.

Diffraction : The curving of a wave around boundaries or barriers or through small openings.

Simulations More simulations More simulations

What happens to a wave when…. …the medium through which it travels changes? The wavelength and the velocity change, but NOT the frequency!

What happens to a wave when…. …it runs into another wave? The two waves will pass through each other At the moment of intersection, the size of the resulting wave is determined by SUPERPOSITION- Adding the amplitudes together.

Constructive Interference: Waves are on same side of equilibrium Waves are on same side of equilibrium

Destructive Interference: waves are on opposite side of equilibrium

What happens when…. … a wave reflects back upon itself? It MAY result in a standing wave. Node: the locations along a standing wave where the medium is undisturbed. Antinode: the locations where there is maximum displacement.

Sound

I. Sound is a longitudinal wave. * A.Molecules move parallel to the direction of the waves velocity. B.Areas of high pressure and low pressure C.“compression” and “rarefaction”

II. Requires a vibrating object A.Guitar string B.Stereo speaker C.Voice: vocal cords *

III. Speed A.At standard temp and pressure, v = 343 m/sv = f B.As the temp goes up, the velocity increases C.As the density of the medium goes up, the velocity increases D.Travels much slower than light Count time to thunder- divide by 5 III. Speed A.At standard temp and pressure, v = 343 m/sv = f B.As the temp goes up, the velocity increases C.As the density of the medium goes up, the velocity increases D.Travels much slower than light Count time to thunder- divide by 5

The velocity of a wave depends on the medium through which is travels. If you know the medium, you can also find the velocity by Bulk modulus- fluids Elastic modulus- solids

What kind of sound wave is produced when the source of the sound is moving?

Sonic booms occur when the source of sound exceeds the speed of sound * Sonic Booms captured on video Sonic Booms captured on video

IV. Reflection A.Echo B.Sonar: invented in 1915 C.Ultrasound D.Autofocus cameras

V. Pitch A.Determined by the frequency B.Hi frequency = high pitch C.Musical notes- if you double the frequency you go up by one OCTAVE Example: 400 Hz, 200 Hz, 800 Hz A.Range of hearing humans 20 Hz up to about 20,000 Hz dogsup to about 50,000 Hz catsup to about 70,000 Hz

VI. Doppler Shift Doppler Shift Doppler Shift A.A detected change in the frequency of a wave as the source of the wave moves B.Police siren, weather, stars Police sirenPolice siren

Wave Amplitude For a sound wave, the wave amplitude corresponds to the VOLUME. Loudness is measured in decibels, dB Where zero decibels is the threshold of human hearing and 120 dB is the point at which sound becomes painful and hearing can be damaged.

Resonance  If two objects are vibrating with the same frequency, they are said to be in “resonance”  Examples: two tuning forks  Tacoma Narrows bridge A “driven” oscillator A “driven” oscillator

Beats  A “beat frequency” is produced when two objects are vibrating at nearly the same frequency.  Used for tuning orchestral instruments Beat frequency = f 1 – f 2

Resonators  All musical instruments create standing wave forms within them.  Wind instruments: waves of air molecules inside the cavities  Stringed instruments have vibrating strings, but the majority of sound is produced when that vibration is spread to a resonating box, often called the “sound board”

“Open Pipe” resonator  a node at each end  “fundamental frequency”- the lowest note produced  Length of pipe = ½ of a wavelength

Harmonics  Other frequencies, called “harmonics” are produced AT THE SAME TIME as the fundamental frequency.  2 nd Harmonic  Length = one wavelength

 3 rd Harmonic  Length = 1 ½ wavelengths

Closed Pipe Resonators  Node at open end. Antinode at closed end.  Fundamental frequency:  Length = ¼ of a wavelength

Closed Pipe Resonators 2 nd Harmonic  Length = ¾ of a wavelength

For the same length, which type of organ pipe will produce a lower note, an open pipe or a closed pipe? A closed pipe!

Copy this: Standing Waves and Harmonics 1. Draw three 10-cm. (0.10 m) long open “pipes” 2. Draw the fundamental, second and third Harmonic standing waves. 3. Determine the wavelength and the frequency of each of the three waves. v = 343 m/s and v = f