Vibrations and WavesWhat are waves?

A waves is a disturbance that repeats in spaces and time and that carries energy from one region to another.

A vibration is a wiggle in time. We can create this vibration by disturbing the medium (solid, liquid, or gas)- vibrations cause waves

Waves carry energy and information from one place to another, but they do NOT carry particles or matter along with them. Through wave motion, energy is transferred from a source to the receiver.

Wave CharacteristicsAmplitude-the height if the wave measured

from the baseline to the top of the wave crest or the bottom of the trough; indicates the energy of the wave.

Wavelength-the distance between any two adjacent corresponding locations on the wave; crest to crest or trough to trough; symbol is the Greek letter lambda λ

Characteristics cont.Crest-highest point on the wave

Trough-lowest point on the wave

Baseline-the point at which the wave is in equilibrium

Frequency-the number of vibrations or wavelengths per second; measured in Hertz (Hz)

1 Hertz = 1 wave/sec

Characteristics cont.Period-the amount of time it takes to make on

complete wavelength; measured in seconds; symbol is T

period = sec/cycle OR 1/frequency

Wave Speed-depends on the medium in which the wave travels; in a given medium the speed is constant; measured in m/sec

wave speed = frequency X wavelength υ = f X λ

Collisions of WavesThe interaction between two or more waves

that produces a new wave is called interference.

Constructive interference-when the amplitudes of the initial waves are in the same direction (two crest combine); the waves are “in phase”. The resulting wave is larger than the original wave

Collisions of Waves cont.Destructive interference-when the

amplitudes of the initial waves are in the opposite direction (crest of one wave and the trough of another); these waves are “out of phase”; the amplitude of the resulting wave will be zero

Types of WavesLongitudinal waves

+Causes the medium to move parallel to the direction of the wave

+Particles of the medium move horizontally, but not up and down

+Examples: sound waves, shock waves, and some types of seismic waves

Types of Waves cont.Transverse Waves

+Cause the medium to move perpendicular to the direction of the wave

+Particles to the medium move up and down, but not horizontally

+Examples: waves on a rope, shaking a blanket, the “wave” at a sporting event, electromagnetic waves (radio, microwaves, infrared, visible, ultraviolet, x-rays and gamma)

Types of Waves cont.Surface waves

+A combination of longitudinal and transverse waves

+Example: water waves

Mechanical waves+Require a physical medium to travel

through (solid, liquid or gas)+Examples: sounds waves (air), seismic

waves (Earth’s crust)

Types of Waves cont.Electromagnetic Waves

+Do not require a physical medium to travel through, although they can travel through them

+Travel at the speed of light+Examples: light waves and

electromagnetic waves

Traveling wave-one in which it is readily apparent that the wave exhibits forward movement; it is possible to track the progress of peaks and troughs

Types of Waves cont.Standing wave-one in which certain points,

called nodes, appear to remain motionless. Standing waves are the basis fro producing musical sounds.

Just as node is a point of stillness or no motion, the antinode is a point of maximum motion. Antinodes are spaced evenly between the nodes in standing waves.

Standing waves are created by the constructive and destructive interference if the incident and reflected waves.

Sound WavesWhenever an object vibrates, it causes the air

around it to vibrate also. These vibrations spread out and travel as pulses or waves called sound waves.

Sound waves are mechanical, longitudinal wavesSound waves are made of 2 parts

+compression-as the vibrations move through the air, the forward vibration of the molecules ahead to be pushed close together or compressed (comparable to the crests)

+rarefaction-when the molecules vibrate backward, they become spread further apart or rarefied (comparable to the trough)

Sound Waves cont.3 aspects of sound:

+source: the source of a sound wave is a vibrating object

+energy is transferred from the source in the form of longitudinal sound waves

+sound is detected by an ear or an instrument- receiver

Velocity of SoundMost sounds we hear are transmitted through

air. Compared to solids and liquids, air is a relatively poor conductor of sound.

The velocity of sound in water is 4 to 5 times faster than in air.

The velocity of sound through steel or other metals is 15 to 20 times faster than air.

***Sound will not travel in a vacuum. The transmission of sound requires a medium; if there is nothing to compress and expand, there can be no sound.***

Sound Waves cont.Loudness is related to the energy in the sound

wave. The loudness of a sound depends primarily upon the amplitude of the sound wave.+the greater amplitude produces a louder sound+Pitch refers to whether the sound is high or low. High pitch sounds are produced by sources vibrating at high frequency; low pitch sounds are produced by sources vibrating at low frequency+Loudness is measured in decibels

Sound Waves cont.

Sound Waves cont.Pitch corresponds to frequency. Different

musical notes are obtained by changing the frequency of the vibrating sound source. This is usually done by altering the size, the tightness, or the mass of the vibrating object.

High pitch sounds used in music are most often less than 4000 Hz. The human ear can hear sounds up to 18,000 Hz. The upper limit of hearing in people gets lower as they grow older.

Sound Waves cont.The Doppler Effect refers to the change in

pitch (shift in frequency) of a sound due to the motion either of the source or the listener. If they are approaching each other, the pitch is higher. If they are moving apart, the pitch is lower.

Period vs. FrequencyThe frequency of a wave measures how many

cycles of the wave pass a fixed point per unit time.The unit of frequency is cycles per second:

1 cycle/sec = 1 Hertz = 1 Hz

Remember that the period of a wave is how many seconds are in one cycle.

The unit of period is seconds per cycle or seconds

Looking at the units of frequency and period, it becomes clear that one is the reciprocal of the other.

Wave SpeedThe speed of the wave depends on the medium

through which the wave moves.

A relationship exists between speed, frequency and wavelength

wavelength = frequency X wavelength

υ = f X λ

υ = wave speed (m/sec)F = frequency (Hz)Λ = wavelength (m)

Wave Speed cont.Sample Problems:1.What is the wavelength of a 340 Hz sound

wave when the speed of sound in air is 340 m/sec?

2. What is the frequency of a wave whose speed is 340 m/sec and wavelength is 0.64 m?

Light WavesLight can pass through, bounce off, and be absorbed

by matterLight is electromagnetic radiationAll electromagnetic radiation forms transverse

electromagnetic wavesLight travels through space at 3 X 10 8 m/secLight can travel in a vacuumLight travels in a straight lineLight is a form of energy known as radiant energyLight does not need a medium to travel through,

although it CAN travel through a medium

Light Waves cont.No kind of matter transmit 100% of the light

that strikes it. Nothing reflects 100% or absorbs 100% of the light.

Transparent objects (glass, air, water) transmit light readily, allowing objects to be easily seen through them

Translucent objects readily allow light to penetrate them but light is scattered and objects appear distorted

Opaque objects prevent transmission of nearly all light rays

Light Waves cont.Electromagnetic spectrum- an arrangement of all

electromagnetic radiation by wavelength, frequency, and energy

The order is as follows (highest energy-shortest wavelength)Gamma rays-emitted in nuclear reactions (fusion,

fission); absorbed by heavy metals and the earth’s atmosphere

X-rays-used in medicine; absorbed by heavy metals and the earth’s atmosphere

Ultraviolet-causes sunburn, suntan, skin cancer; not completely absorbed by the earth’s atmosphere

Light waves cont.Visible light-the only type of electromagnetic

radiation that we see; ROYGBIVInfrared-warm objects emits thisMicrowave-used in cooking because water

absorbs it wellRadio waves-used in communication (lowest

energy-longest wavelength

All types of electromagnetic radiation travel at the speed of light but differ in wavelength and frequency

Light waves cont.Reflection-refers to the rebounding of light rays off an

objectObjects are visible to us because of the light they

transmit to our eyesRough, light-colored surfaces, such as sand and

paper, reflect much light. Smooth, shiny surfaces also reflect much light but in a different way. If you look at a shiny surface, you can see a likeness of image of objects facing the surface.

If you shine a beam of light on a mirror, the light does not travel through the mirror, but it is returned at the surface back into the air.

Reflected waves simply travel back in the direction from which they came.

Light waves cont.The Law of Reflection describes light as “the angle

of incidence is equal to the angle of reflection”

θi = θr

where θi is the angle of incidence and

θr is the angle of reflectionIncident ray- the ray of light that strikes an objectReflected ray- the ray that rebounds from a surfaceNormal-an imaginary line that is perpendicular to

the surface

Light waves cont.Reflection

Light waves cont.Refraction-the bending of light when it

passes from one medium to anotherExample: when light passes from air into

glass, it is bent. This is the principle that lens-makers use in creating glasses and contacts

All electromagnetic waves, including light, travel in a vacuum at the rate of 3.00 X 108 m/s

In other media, light slows down

Light waves cont.Refraction

Light waves cont.“Refraction in Action” An apparently “wet” road-refraction of light by

warm air near the road gives use to the “wet” spot on the road surface (a mirage)

Hot air rising from a road surface-due to a property of gases that makes us sense the gas is rising when heated

Twinkling of stars-air through which starlight travels continually changes in density due to temperature changes and turbulance

“Not where it should be”- trying to reach something underwater-the object appears to be closer to the surface than it actually is

ColorThe color of an object depends upon the

wavelengths of light that the objects absorbs, transmits, or reflects

Black objects absorb most of the visible light that is incident on them

White objects reflect most of the visible light that is incident on them

Because of this, we say that black is not a color, but rather is the absence of color.

Conversely, white light includes all wavelengths of visible light-white light is not a color, but rather a sum of all colors.

Color cont.The primary colors of light are red, green,

and blue, not red, blue and yellow (these are the primary pigments). White light is the sum of these 3 primary colors.