Chapter 15 WAVES

Waves

• Wave a disturbance that transfers energy through matter or a medium.

Waves

- waves transfer energy http://www.youtube.com/watch?v=Y dnv2xo9Ndw -Most waves are caused by vibrating objects.

Types of Waves

1. Mechanical wave a wave that requires a medium to travel through.

Ex.

Sound, ocean waves,earthquake waves

Types of Waves

2. Electromagnetic wave a wave that does NOT require a medium to travel through.

- these pass though by magnetic fields or electromagnetic fields Ex.

light

Wave Forms

1. Transverse waves a wave that causes the particles to vibrate perpendicular to the direction the wave travels Ex.

Stadium wave, radio waves, Heat waves,

Wave Forms

2. Longitudinal waves a wave that causes the particles of the medium to vibrate parallel to the direction the wave travels.

Ex.

Sound wave, compression wave

Wave Forms

3. Surface waves – particles move both perpendicular and parallel to the direction in which the wave travels.

Ex.

Sound Wave

Sound wave – require a medium to travel through.

- longitudinal waves - causes the particles of the medium to vibrate parallel to the direction the wave travels.

Wave Properties

• Wavelength The distance between any one point on a wave to an identical point on next wave.

Determines the type and color of the wave.

Wave Properties

- crest The top of a wave - trough The bottom of a wave

Wave Properties

• Amplitude Half the distance from the crest and the trough.

- determines the loudness of the sound.

Wave Properties

• period The time it takes a complete wavelength or wave oscillation to occur.

- same distance as the wavelength.

Wave Properties

• frequency How many waves created in a given time; the number of cycles or vibrations in a given time. - SI label is Hertz (Hz) - determines the pitch of the sound.

- high frequency = high pitch.

Frequency wave

Wave Speed

• Wave speed (v)- the speed of a wave is equal to wavelength divided by period, or frequency multiplied by wavelength.

Two ways you can find wave speed: - wave speed (v) = wavelength/period OR v = frequency x wavelength

Wave Speed

• Ex. Waves passing by a pier have a frequency of .5 Hz and a wavelength of 10 m. What is the wave speed?

Determinates of wave speed:

-The medium determines the speed of the wave.

Ex. Sound: travels fastest in solid ( 15-20 x faster than air ) travels fast in liquid travels slowest in air (about 340 m/s) Ex. Light: travels fastest in empty space (c = 3 x10 8 m/s or 186,000 mi/s) slows down when it has to go through air or water

Determinates of wave speed:

Kinetic energy explains this.

In air, molecules are far apart and won’t hit one another quickly. In solids, they are very close and will easily hit (vibrate) one another.

Doppler Effect

•

Doppler effect

– an observed change in frequency of a wave when the source or observer is moving.

Doppler Effect

• As the ambulance is coming towards you, the siren sound is hitting you quicker, so the pitch is higher. As the ambulance is going away from you, the siren sound is going away, so it takes longer to hit your eardrum, so the pitch is lower.

http://videos.howstuffworks.com/discovery/27963 assignment-discovery-doppler-effect-video.htm

Wave Interactions

• What happens when a wave meets an object or another wave?

– Waves can reflect, diffract, refract or interfere

Reflection

•

Reflection

-The bouncing back of a wave when it meets a surface or boundary • Examples: – Water waves reflect off the side of a boat – Light waves reflect off the surface of a lake

Diffraction

•

Diffractio

n-A change in the direction of a wave when the wave meets an obstacle (ex. An opening) • Examples: – Sound waves diffract around corners – Water waves diffract around r ocks http://phet.colorado.edu/en/simulation/wave interference

Refraction

• Refraction-The bending of a wave when it passes between 2 mediums in which the speed of the wave differs • Example: Straw in water

Interference

• Interference-The combination of 2 or more waves that result in a single wave

Interference

• Constructive interference-The combination of 2 or more waves that produce a wave with an increased amplitude • Destructive interference-The combination of 2 or more waves that produce a wave with a decreased amplitude

Interference

Interference: Sound Waves

• Interference of sound waves produce beats – Beats-A pattern of alternating loud and soft sounds

Interference: Light Waves