……A MOVEMENT OF A MOVEMENT OF ENERGYENERGY

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

SURFACE WAVES

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 WaveParts 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 When light enters a particular medium at an angle (or enters a prism) the wave will an angle (or enters a prism) the wave will change it’s change it’s speedspeed; speed depends upon ; speed depends upon wavelength, and since the colors that wavelength, and since the colors that make up light have different wavelengths, make up light have different wavelengths, they have different speeds and will then they have different speeds and will then be visible; be visible; Frequency did not change, that property Frequency did not change, that property depends upon the source, not the depends upon the source, not the medium.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 heard 0dB

Whisper Quiet Library 30dB

Normal conversation (3-5') 60-70dB

Telephone dial tone 80dB

City Traffic (inside car) 85dB

Train whistle at 500', Truck Traffic 90dB

Subway train at 200' 95dB

Level at which sustained exposure may result in hearing loss 90 - 95dB

Power mower at 3' 107dB

Snowmobile, Motorcycle 100dB

Power saw at 3' 110dB

Sandblasting, Loud Rock Concert 115dB

Pain begins 125dB

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 Blast 140dB

Death of hearing tissue 180dB

Loudest sound possible 194dB

 

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