Chapter 10 Sect. 1 The Nature of Waves

Wave—a repeating disturbance or movement that transfers energy through matter or space Ex: ocean waves (resulting from earthquakes Waves carry energy without transporting matter from place to place. All waves are produced by something that vibrates. A wave will travel only as long as it has energy to carry

Medium-the matter that waves travel through Ex: sound waves through air, etc. Not all waves need a medium (light waves) Medium can be a solid, liquid, gas or combination of these

Mechanical Waves—have to have a medium to travel (air, water or some other medium) There are two types: Transverse: matter in the medium moves at right angles to the wave motion (zig-zag movement) ex: water waves Compressional: matter moves in the same direction as the wave movement (straight line motion w/no crests and troughs, instead compressions and rarefactions) ex: sound waves

Sound waves Can travel through air, water, solids like steel and wood Particles in these mediums are pushed together and move apart as sound waves move through them When a sound wave reaches your ear, it causes your eardrum to vibrate then signals messages to your brain

Water Waves Not purely transverse waves There is a combination of up and down and back and forth motion Therefore, water moves in circles (Also: wind speed changes vibration of the waves )

Seismic waves Combinations of compressional and transverse waves They travel through the Earth’s crust after an earthquake and cause great damage to houses, buildings, structures

Section 2: Wave Properties

Parts of a Wave Crests—the highest points of a transverse wave Troughs—lowest points of a transverse wave (transverse waves have alternating high pts and low pts)

Compressional waves -have no crests and no troughs More dense area of the wave— compression Less-dense region of the wave-- rarefaction

Wavelength Wavelength—property of a wave –The distance between one point on a wave and the nearest point just like it. –(measured from crest-crest or trough-trough OR compression to compression or rarefaction to rarefaction)

Frequency Frequency of a wave is the # wavelengths that pass a fixed point ea/second. –Expressed in Hertz (Hz) –Hertz is the same as 1/s

More on wavelengths and frequency With transverse waves, when frequency increases, wavelength decreases Frequency of a wave = rate of vibration of the source that creates it

Wave Speed Speed of a wave depends on the properties of the medium it is traveling through –Ex: sound waves travel faster in liquids and solids than in gases –Ex: light waves travel more slowly in liquids and solids than they do in gases

Calculating Wave Speed Speed = wavelength X frequency OR V = wavelength X f (pg. 335)

Amplitude and Energy Amplitude—related to the energy carried by a wave The greater the waves amplitude, the more energy the wave carries Amplitude is measured differently for compressional and transverse waves

Amplitude of Compressional Waves Related to how tightly the medium is pushed together at the compressions Denser medium, larger amplitude, more energy the wave carries The closer the coils are in a compression, the farther apart they are in a rarefaction, & the more energy carried

Amplitude of Transverse Waves Amplitude of a transverse wave increases as the energy carried by the wave increases A tall ocean wave has a greater amplitude than a short ocean wave