Waves

What is a wave?

• A wave is a repeating disturbance or movement that transfers energy through matter or space.

Waves and Energy

• Waves and Matter– Waves transfer energy without transferring

matter from place to place• In the water energy is transferred from water

molecule to the next water molecule, that is why a boat doesn’t move much.

• A boat will move some in waves, especially up and down. That is because only a small amount of energy is transferred to the boat.

Waves and Energy

• Making Waves– A wave will only travel as long as it has

energy transfer.– All waves are produced by something that

vibrates

Mechanical Waves

• Medium – matter the waves travel through– Medium can be a solid, liquid, gas or a

combination of these.– Not all waves need a medium– Waves that can travel only through matter are

called mechanical waves • Two types – transverse and compressional

Mechanical Waves

• Transverse Waves – Transverse wave the medium moves back

and forth at right angles to the direction that the wave travels,

• Shaking a rope up and down, waves in the ocean

Mechanical Waves

• Compressional Waves– Compressional Waves matter in the medium

moves back and forth along the same direction the wave travels

• Holding several coils together in a spring and then letting go

• They are also called longitudinal waves

Mechanical Waves

• Sound Waves– Sounds waves are compressional waves– Vibrations push air molecules together by

vibrations made.

• Sound in Other Materials– Sound can travel in other meduim such as

water and wood.– Sound reaches your ear it causes your ear

drum to vibrate and brain interprets the signals as sound

Mechanical Waves

• Water Waves– Not purely transverse waves, also moves a

short distance back and forth along the direction the wave is moving.

Mechanical Waves

• Seismic Waves– Seismic waves are a combination of

compressional waves and transverse wave– When objects on Earth’s surface absorb some

of the energy transferred by seismic waves they move and shake

Parts of a Wave

• Transverse wave– Crest – High point of a Wave– Trough – Low points of a waves

• Compressional Wave– Compressions – region where coils are close

together– Rarfactions – spread apart or less dense

Wavelength

• Wavelength – Distance between one point on a wave and the nearest point just like it.– Crest to Crest, Trough to Trough, Rarefaction

to Rarefaction, Compression to compression.– High sounds have shorter wavelengths(few

centimeters), Low sounds have longer wavelengths (many meters).

Frequency and Period

• Frequency – the number of wavelengths that pass a fixed point each second– Frequency is expressed in Hertz (Hz)

• Period – amount of time it takes one wavelength to pass a point– As the frequency of a wave increases the

period decreases.

Frequency and Period

• Wavelength is related to frequency– As frequency increases, the wavelength

decreases.

Wave Speed

• The speed of the wave depends of the medium it is traveling through.

• Sounds waves usually travel faster in liquids and solids than they do in gasses.

• Light waves travel more slowly in solids and liquids than they do in gasses or empty space

• Waves travel faster in a medium when the temp is increased

Wave Speed

• Calculating Wave Speed– Speed = frequency x wavelength

Amplitude and Energy

• Amplitude – related to the energy transferred by a wave. The greater the waves amplitude the more energy the wave transfers

Amplitude and Energy

• Amplitude of a Compressional Wave– Related to how tightly the medium is pushed

together at the compressions– Denser the medium is at the compressions,

they larger the amplitude is and the more energy the wave has.

Amplitude and Energy

• Amplitude of a Transverse Wave– Amplitude of a transverse wave is the

distance from the crest or the trough of the wave to the rest position.