Ch. 10,11, 13 Waves. Name some waves Water Sound Light Radio waves (TV) Microwaves (cell phones)...
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Transcript of Ch. 10,11, 13 Waves. Name some waves Water Sound Light Radio waves (TV) Microwaves (cell phones)...
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 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
Behavior of Waves
• Reflection: when a wave hits an object and bounces off
• Examples:
echos = sound waves
image in mirror = light waves
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
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
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
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.
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.
• http://www.archive.org/details/SF121