Ch. 10,11, 13 Waves

Name some waves Water Sound Light Radio waves (TV) Microwaves (cell phones) X-rays Ultrasound Earthquakes! (seismic waves)

Definition Wave: repeating disturbance or movement that transfers energy through matter or space. How does it transfer energy? By making things MOVE

Mechanical Waves Mechanical Waves: travel through a medium - sound waves, water waves Medium: Solid, liquid or gas Light doesn’t need a medium Sound waves DO

Types of Mechanical Waves Transverse: side to side motion 90º to the direction of wave travel; ocean, seismic s- waves Compressional: back and forth in the direction of wave motion; sound waves, seismic p-waves

Other mechanical waves Water waves: combination transverse and compressional Seismic waves: earthquakes s-waves = transverse p-waves = compressional

Wave Properties - Transverse Wavelength: distance between 2 crests Wavelength λ Amplitude (at crest) Trough

Wave Properties – Compressional Wavelength: distance between 2 compressions

Comparison

Compressional and Transverse

Transverse Wave

Compressional Wave

Water Wave Watch the blue particle

Wave Characteristics Frequency- f: # of waves that pass a point per second. Unit = Hertz (Hz) = 1 / second Higher frequency = shorter wavelengths Period-T: Amount of time it takes for one complete wave to pass a point Unit = seconds T = 1/f

Amplitude and Energy Amplitude = height of crest or depth of trough OR Amplitude = density of the compression Greater amplitude = greater energy Ever been knocked down by a BIG wave at the beach? Two waves with equal frequency and wavelength – the larger amplitude wave has the greater energy.

Wave parts Transverse parts Crest – top of the wave (or a toothpaste) Trough bottom of the wave Wavelength- space between two crests or troughs Compression parts Rarefaction- less dense area Compression- more dense area Wavelength- space between compressions or refractions

Wave speed Different waves have different speeds Light is faster than sound waves Baseball stadium cheap seats: See the ball hit before you hear it

Wave Speed Sound moves faster in solids/liquids than air Light waves move more slowly in liquids

Wave Speed Calculating wave speed: v = f∙λ where v = wave speed λ = wavelength f = frequency

Example λ = 4 m, f = 2 Hz, v = ? v = f ∙ λ = 4 m ∙ 2 Hz = 8 m/s v f λ

Example v = 14 m/s, f = 2 Hz, λ = ? v = f ∙ λ 14 = 2 Hz x λ 14 / 2 = λ λ = 7 m v f λ

Behavior of Waves Reflection: when a wave hits an object and bounces off Examples: echos = sound waves image in mirror = light waves

Law of Reflection Angle of incidence = Angle of reflection

Refraction The bending of a wave caused by a change in it’s speed as it moves from one medium to another Air Water

Example Standing in pool, legs look shorter Look at object at bottom of bathtub and try to grab it

Refraction

Diffraction Diffraction: occurs when an object causes a wave to change direction and bend around it Look closely at a shadow – transition area between light and dark Shine light through thin slit – see diffraction and interference

Diffraction

Interference when two or more waves overlap and combine to form a new wave Constructive: add to each other Destructive: subtract or cancel each other

Constructive Interference

Standing Waves wave pattern that forms when waves of equal wavelength and amplitude but opposite directions continuously interfere Nodes: zero amplitude Examples: musical instruments – strings, woodwinds, etc.

Standing Waves

Resonance when an object vibrates at it’s natural frequency. Example: ringing bell, tubular chimes, tuning fork Badly balanced tires on a car – resonance at certain speeds.