What are waves?

Wave Review:

Definition: A disturbance that transfers energy from place to place.

What carries waves? A medium, a medium is the material through which a wave travels.

A medium can be a gas, liquid, or solid.

Not all waves require a medium to travel.

Light from the sun travels through empty space.

What causes waves?Waves are created when a source of energy causes a medium to vibrate.

A vibration is a repeated back and forth or up and down motion.

Types of waves: Waves are classified according to how

they move.

Transverse waveWaves that move the medium at right angles to the direction in which the waves are traveling is called a transverse wave.

Transverse means across.The highest parts are called crests the lowest parts are called troughs.

Longitudinal/Compressional Wave

Matter vibrates in the same direction as the wave travels.

Example: Slinky

Combinations of wavesSurface waves are a combination of transverse and longitudinal waves.The waves occur at the surface between water and air.

Properties of Waves

Basic Properties of Waves

Amplitude

Wavelength

Frequency

Speed

Amplitude

Amplitude is the maximum distance the particles of the medium carrying the wave move away from their rest positions.

The farther the medium moves as it vibrates the larger the amplitude of the resulting waves. The greater the amplitude the greater the amount of energy

Amplitude of transverse waves

The amplitude of a transverse wave is the maximum distance the medium moves up or down from its rest position. You can find the amplitude of a transverse wave by measuring the distance from rest to crest or rest to trough.

Amplitude of a longitudinal wave.

The amplitude of a longitudinal wave is a measure of how compressed or rarefied the medium becomes.

WavelengthA wave travels a certain distance before it starts to repeat. The distance between two corresponding parts of a wave is its wavelength.

Transverse measure from crest to crest or trough to trough.

Longitudinal measure from one compression to the next.

Frequency

The number of complete waves that pass a given point in a certain amount of time.

AKA number of vibrations per second.

Frequency measured in hertz (Hz).

Speed

The speed, wavelength, and frequency of a wave are related to each other by a mathematical formula.

Speed = wavelength x frequency

Frequency = speed/wavelength

Wavelength = speed/frequency

Ways Waves InteractInterference

Constructive

Destructive

Standing Waves

Reflection

Refraction

Diffraction

Interference

Constructive interference occurs whenever two waves combine to make a wave with a larger amplitude.

Destructive interference when the amplitudes of two waves combine producing a smaller amplitude.

Standing waves:If the incoming wave and the reflected wave combine at the right places the combined wave appears to be standing still.

It appears to be standing in one place, even though it is two waves interfering as they pass through each other.

Nodes and AntinodesNodes: at certain points, destructive interference causes the two waves to combine and produce an amplitude of zero.

Antinodes are the points of maximum energy. The crests and troughs of a standing wave.

ResonanceMost objects have a natural frequency of vibration. Resonance occurs when vibrations traveling through an object match the object’s natural frequency.

An object that is vibrating at its natural frequency absorbs energy from the objects that vibrate at the same frequency. This often occurs in music.

Resonance: GuitarsWhen you pluck a single guitar string, hardly any sound is heard

When the same string is on a guitar and plucked, the intensity increases dramatically. This is called forced resonance.

The vibrating of the string causes the body of the guitar to vibrate as well.

The forced vibrations are called sympathetic vibrations.

More Examples of ResonanceEx 1: Tacoma Narrows Bridge

the wind blowing through the canyon matched the natural frequency of the bridge, causing it to oscillate and eventually crumble.

http://www.youtube.com/watch?v=3mclp9QmCGs

More Examples of Resonancehttp://www.youtube.com/watch?v=dU0OqVDl7kc&feature=related

Ex 2: Wine glasses

Singers can match the natural frequency of the glass with their voices, causing the glass to vibrate and eventually shatter.

More Examples of ResonanceEx 3: A child on a swing

A child pumps their legs in rhythm with the natural frequency of the swing, moving higher and higher.

ReflectionWhen an object or wave hits a surface through which it cannot pass, it bounces back.

KEY IDEAS:

Angle of incidence

Angle of reflection

Examples of reflection

Ball against a wall

Mirror (light waves)

Echo (sound waves)

Reflection Diagram

Refraction is when a wave moves from one medium into another medium at an angle, it changes speed as it enters the second medium which

causes it to bend. The bending of waves due to a change in speed is called

refraction.

RefractionThough all waves change speed when they enter a new medium. Bending occurs when one side of the wave enters the new medium before the other side

Diffraction

When a wave passes a barrier or moves through a hole in a barrier it bends and spreads out.