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