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

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

Electromagnetic Waves They can travel through empty space- a vacuum- they don’t require a material medium. Examples: x-rays, UV, visible light, infrared, … 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

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- Measured in meters

Amplitude, A Maximum distance above or below equilibrium- Measured in meters As the amplitude increases, the energy the wave transmits also increases.

Period, T Shortest time interval during which the pattern repeats- -- measured in seconds Frequency, f The number of waves per second-- Measured in Hz f = 1 / T and T = 1 / f Example: While watching waves go by a pier, you count 6 waves every 12 seconds. What is the frequency and period of the waves? f = 6 waves / 12 s = 0.5 Hz T = 1 / f = 2 s

Velocity, v The velocity of a wave depends on what kind of material through which it is traveling. For example, ALL sound waves, regardless of their pitch, travel at the same speed through air and at the same speed through water. But the speed in water is faster than the speed in air!

The velocity of a wave depends on the medium through which is travels. If you know some things about the medium, you can find the velocity by “Modulus”- a characteristic of different substances Bulk modulus- fluids Elastic modulus- solids

Velocity, v You can find that speed if you know both the wave’s period and its wavelength: Velocity = Distance / time = /T, so v = /T but since frequency, f = 1/T, v = f

Water Wave “Surface” water 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

Get a calculator!!!

Period = time per wave Frequency = waves per time If you observe 3 waves go by every 9 seconds, what is the period of the wave? The frequency? T = 3 sf = 1/3 Hz

A sound wave moves at about 343 m/s through air. The musical note “C” has a frequency of 128 Hz. What is its wavelength in air? v = f = v/f= v/f = 343 m/s / 128 Hz = 2.7 m

What is the frequency of red light, whose wavelength is 620 nm? nm = m Velocity = c = 3 x 10 8 m/s v = f f = c / f = c / f = 3E8 / 620E -9 f = 4.8E14 Hz

Two different sound waves are produced by different band instruments- 512 Hz and 106 Hz. Which has a longer wavelength? Since the velocity is the same for both, the smaller frequency has the larger wavelength! v = f