# WAVE INTERACTIONS Waves transfer energy without transferring matter

• Slides: 38

WAVE INTERACTIONS

Waves transfer energy without transferring matter.

Mediums Most waves require a medium to travel through. These are called Mechanical Waves. A medium is any matter that a wave travels through.

Electromagnetic Waves Any wave that does not need a medium to travel through is called an electromagnetic wave. Although we now have gravity waves……. . that are not technically electromagnetic.

Longitudinal Wave wave particles vibrate back and forth along the path that the wave travels. Compressional Wave

Compressions The close together part of the wave Rarefactions The spread-out parts of a wave

Transverse waves wave particles vibrate in an up-and-down motion.

Transverse waves Crests Highest part of a wave Troughs The low points of the wave

Amplitudeis the maximum distance the particles in a wave vibrate from their rest positions.

Wave Length For a transverse wave the wave length is from one crest or trough to another. For a longitudinal wave a wave length is from one compression or rarefaction to another.

Period and Frequency Period the time required for one full wave length to pass. It is represent with T. And is usually measured in seconds

Frequency - the number of waves produced in a given time (usually 1 second). Represented by a lower case f Units are measured in Hz

Wave Velocity - is the speed with which a wave crest passes by a particular point in space It is measured in meters/second. Wave Velocity = Frequency Wavelength

Medium Speed of Sound air (20 C) velocity m/sec 343 air (0 C) 331 water (25 C) sea water diamond iron 1493 1533 12000 5130 copper 3560 glass 5640

The Type of Wave Matters The type of wave also determines the speed. Electromagnetic waves do not need a medium. All electromagnetic waves travel through a vacuum at c = 2. 99792458 x 108 m/s. Put them in a medium and they get bounced around.

Doppler Effect How a wave sounds (pitch) depends upon the frequency. Meaning the more waves pass by in a second the higher the pitch. This can be created by the Doppler effect.

II. Properties of Sound

Pitch - description of how high or low the sound seems to a person . Loudnesshow loud or soft a sound is perceived to be.

Loudness of Sound in Decibels Sound Loudness (dbs) Hearing Damage Average Home 40 -50 Loud Music 90 -100 After long exposure Rock Concert 115 -120 Progressive Jet Engine 120 -170 Pain

Ultrasound waves with frequencies above the normal human range of hearing. Sounds in the range from 20 -100 k. Hz - Infrasound - sounds with frequencies below the normal human range of hearing. Sounds in the 20 -200 Hz range

Interference the result of two or more sound waves overlapping

Different sounds that you hear include (A) noise, (B) pure tones, and (C) musical notes.

Standing sine wave patterns of air vibrating in a closed tube. Note the node at the closed end and the antinode at the open end. Only odd multiples of the fundamental are therefore possible.

Standing waves in these open tubes have an antinode at the open end, where air is free to vibrate.

Standing sine wave patterns of air vibrating in an open tube. Note that both ends have anitnodes. Any whole number of multiples of the fundamental are therefore possible.

Doppler Effect is the apparent change in the frequency of a sound caused by the motion of either the listener or the source of the sound.

Sounds from Moving Sources. A moving source of sound or a moving observer experiences an apparent shift of frequency called the Doppler Effect. If the source is moving as fast or faster than the speed of sound, the sound waves pile up into a shock wave called a sonic boom. A sonic boom sounds very much like the pressure wave from an explosion

Supersonic Flight

Resonance the frequency of sound waves exactly matches the natural frequency of an object.

Water Waves

Tsunami Wave length, 500 to 600 km in ocean

Tsunami Warning • On December 26, they were playing in the sea when Tilly • • suddenly found the water was bubbling, like on top of a beer. She immediately realized tsunami was coming because the scene reminded her of a geography lesson about Hawaii's 1946 tsunami. Right away, Tilly told her parents, sister and other tourists to escape quickly, but at first they were in half belief. However, seeing Tilly's serious and firm expression, people started to be convinced of the seriousness of the thing and instantly left the beach. At last over 100 tourists were ended up in safety with no death

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