…A MOVEMENT OF ENERGY

What are waves? A wave is a movement of energy from a vibrating source outward  A vibration – any movement that follows the same path repeatedly  Vibration = movement = energy Waves carry energy from one place to another

Some waves need something to travel through… Mechanical Waves Waves that require a medium to travel A medium is any form of matter (solid, liquid, gas) The energy moves – not the medium Sound is one example of a mechanical wave

Some waves do not need something to travel through… Electromagnetic Waves Waves that do not require a medium Can travel with or without a medium Light, radio, x-rays, microwaves…..

Waves can be further classified by HOW THEY MOVE TRANSVERSE WAVES LONGITUDINAL WAVES SURFACE WAVES

Transverse Waves Waves that move the medium at right angles to the direction in which the wave is moving Up and Down Light is a transverse wave

LONGITUDINAL WAVES Waves that move the medium parallel to the direction in which the wave is moving Back and forth Sound is a longitudinal wave

A combination of Transverse and Longitudinal Occur between two mediums Up and down with a back and forth motion creates a circle motion

Parts of a Wave

All Waves have FOUR Basic Properties Amplitude Wavelength Frequency Speed

Amplitude The maximum distance the particles of the medium carrying the wave move away from the rest position; Corresponds to the amount of energy in the wave Higher amplitude = more energy

Wavelength The distance between two corresponding parts of a wave Shorter wavelength=more energy! Crest to crest or Trough to trough Compression to compression or rarefaction to rarefaction

Frequency The number of complete waves that pass a given point in a certain amount of time; Higher frequency=more energy The number of vibrations in a second Measured in the Hertz (Hz) 1 Hz = 1 wave per second

Speed How far a wave travels in one unit of time Speed = wavelength x frequency m/s = m x Hz (waves/sec) The type of medium will affect wave speed For example, sound travels faster/slower in different mediums; light travels through water at a different speed than through air

High Frequency, Low Amplitude

High Frequency, High Amplitude

Low Frequency, Low Amplitude

Low Frequency, High Amplitude

A wave with a high amplitude and a frequency of 1.5 Hz 2 sec

A wave with a low amplitude and a frequency of 5.5 Hz 1 sec

Wave Interactions Waves interact with each other and their surroundings Waves interact in FOUR basic ways

When an object or wave bounces back from a surface None of the properties of a wave are changed by reflection. The wavelength, frequency, & speed are same before and after reflection. The only change is the direction in which the wave is traveling.

Reflecting Waves Reflected light waves allow us to see things Reflected sound waves allow echoes to occur If something is not reflected, it may be absorbed by or transmitted through the item

Reflection and sound Echolocation Sonar Ultrasonography

When a wave bends due to a change in speed When a wave moves from one medium to another at an angle, speed changes as it goes into different mediums Due to change in speed, the wave bends

When light waves are traveling through air, they have a certain speed; When they enter the glass, and then the water, their speed changes; To the right is an “overhead” view, showing that the wavelengths changed once the wave entered the new medium

When light enters a particular medium at an angle (or enters a prism) the wave will change it’s speed; speed depends upon wavelength, and since the colors that make up light have different wavelengths, they have different speeds and will then be visible; When light enters a particular medium at an angle (or enters a prism) the wave will change it’s speed; speed depends upon wavelength, and since the colors that make up light have different wavelengths, they have different speeds and will then be visible; Frequency did not change, that property depends upon the source, not the medium. Frequency did not change, that property depends upon the source, not the medium.

The bending of waves around the edge of a barrier When a wave passes through or around a barrier it bends and spreads out

Each of the dark lines represents a barrier that is “in the way of” the wave None of the properties of the wave are changed with diffraction; The wavelength, frequency and speed are the same before and after the diffraction; Again, like with reflection, the only change is in the direction of the wave

When two or more waves meet Constructive Interference  When two waves meet, combine, and create a wave with a larger amplitude  Crest meets crest Destructive Interference  When two waves meet, combine, and create a wave with a smaller amplitude  Crest meets Trough

Resonance Standing waves – those that appear to be still; actually a wave and its reflection experiencing interference as they travel; this occurs a medium’s “resonant frequency.” Resonance occurs when an object that is vibrating at or near another objects natural (resonant) frequency causes that other object/medium to vibrate

SOUND  Sound travels as a longitudinal wave  Energy from a vibration is carried through the medium as the molecules of the medium move back and forth as the disturbance goes by  You hear the sound when (and if) the disturbance reaches the medium near your ear

Speed of sound The speed of sound is dependent upon the properties of the medium through which it travels; those properties include Temperature  Elasticity  Density

Temperature Sound travels slower at lower temperatures Sound travels faster at higher temperatures

Elasticity Sound travels faster in a more elastic medium;  Fastest in solids, slowest in gases  Speed of sound in the ground is four times faster than in air!

Density Density affects the speed of sound when considering mediums that are the same state or phase of matter The less dense the medium, the faster the sound; The more dense the medium, the slower the sound

Chuck Yeager On October 14, 1947, Captain Chuck Yeager became the first person to fly a plane faster than the speed of sound. How did Chuck Yeager “cheat” to break the sound barrier?

Speed of sound and the sonic boom " At sea level a plane must exceed 741 mph to break the sound barrier, or the speed at which sound travels. The change in pressure as the plane outruns all the pressure and sound waves in front of it is heard on the ground as an explosion or sonic boom. The pressure change condenses the water in the air as the jet passes these waves. Altitude, wind speed, humidity, the shape and trajectory of the plane - all of these affect the breaking of this barrier. The slightest drag or atmospheric pull on the plane shatters the vapor oval like fireworks as the plane passes through," he said. "You see this vapor flicker around the plane that gets bigger and bigger. You get this loud boom, and it's instantaneous. The vapor cloud is there, and then it's not there.”

Sonic Boom

What determines the sound you hear? Properties of sound include what you hear and how high or low it sounds. Each of these is dependent upon the properties of the wave producing the sound

Amplitude The amplitude of a sound wave indicates the energy carried by the wave The higher the amplitude, the more intense the sound, or the more loud the sound seems Turn It Off!

The amplitude of sound, or its loudness, is measured in DECIBELs. Environmental Noise Weakest sound heard0dB Whisper Quiet Library30dB Normal conversation (3-5')60-70dB Telephone dial tone80dB City Traffic (inside car)85dB Train whistle at 500', Truck Traffic90dB Subway train at 200'95dB Level at which sustained exposure may result in hearing loss dB Power mower at 3'107dB Snowmobile, Motorcycle100dB Power saw at 3'110dB Sandblasting, Loud Rock Concert115dB Pain begins125dB Pneumatic riveter at 4'125dB Even short term exposure can cause permanent damage - Loudest recommended exposure WITH hearing protection 140dB Jet engine at 100', Gun Blast140dB Death of hearing tissue180dB Loudest sound possible194dB

Frequency Frequency refers to the number of waves that pass a point in a second; The frequency of sound waves indicates the pitch (how high or low) the sound has.

Frequency The lower the frequency, the lower the pitch 700 Hz sound The higher the frequency, the higher the pitch 1400 Hz sound Turn It Off!

Draw a sound wave with a high pitch and low volume.

Draw a sound wave with a loud volume and a high pitch

Draw a sound wave with a low pitch and high volume.

Draw a sound wave with a low pitch and low volume.

The Doppler Effect The apparent change in frequency as the wave source moves in relation to the listener This is heard as a change in pitch

Assignment Complete page 605 #’s 2-5 Read pages 606 – 611; add info to your notes if necessary Complete page 611 #’s 3-5, 7-10