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WAVES
Waves
• A wave is any disturbance that transmits ENERGY through matter and space.
• Waves carry energy NOT matter.
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Kinds of Waves
– Longitudinal Wave
• The material that the wave is in vibrates back and forth along the path that the wave travels.
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Kinds of Waves
– Transverse Wave• The material that the wave is in moves
perpendicular (at right angles) to the direction that the wave is traveling.
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Longitudinal Waves• Compression
– Section of a longitudinal wave where the particles are crowded together
• Rarefaction– Section of a longitudinal wave where the
particles are less crowded than normal
Transverse Waves
• Crests– The highest point in a transverse wave.
• Troughs– The lowest point in a transverse wave.
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Crest and Trough
Amplitude
• Amplitude– Maximum distance the wave vibrates
from its rest position
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Which one of these waves has a larger amplitude?
Wavelength• Wavelength (λ)
– The distance from any point on one wave to that same point on the next wave
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SIM2
λ
λ
The wavelength of a longitudinal wave can be measured as the
distance between the center of two compressions or
rarefactions.
Which one of these waves has a larger wavelength (λ)?
Frequency• Frequency
– The number of waves (or cycles) produced in a given amount of time
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Which one of these waves has a higher frequency?
Review
Reflection
• Reflection– When a wave bounces back after striking a
barrierSIMSIM2
Refraction
• Refraction– The bending of a wave as it passes at an angle
from one material (medium) to another.
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Diffraction
• Diffraction– The bending of waves around a barrier or
through an opening.
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Interference
• Interference is the result of two or more waves overlapping.
• Constructive Interference– Occurs when the crests of one wave overlap the
crests of another wave OR the troughs of the waves overlap
Interference
• Destructive Interference– Occurs when the crests of one wave and the
troughs of another wave overlap
Standing Waves
• Standing wave SIM– A wave that forms a stationary pattern. – Portions of the wave do not move and other
portions have a large amplitude– At rest= total destructive interference – Large amplitude=constructive interference.
Sound waves are reflected at a
boundary.(SIM1) (SIM2)
Sound waves are refracted at a boundary.
Interference.– Constructive interference– Destructive interference
Here’s what is occurring.
(SIM1)(SIM2)
SIM - Interference
Multiple sound sources interfere (SIM)
Changing separation distance.
Multiple sound sources interfere.
Changing source frequency.
What is a Medium?
• A substance through which a wave can travel– Water– People– Air– Coiled wire
What is a Mechanical Wave?
• A wave that requires a medium
• Examples:– Sound– Water
Resonance
• Objects have resonant frequencies
• An object vibrating at the resonant frequency of a second object causes the second object to vibrate too!
SIM - Resonance
What Effects The Speed of Sound?
• Medium
What Effects The Speed of Sound?
• Temperature
• As the temperature rises, the sound travels faster!
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Pitch
• How high or low you perceive a sound to be
• Determined by the frequency
High Pitch
Low Pitch
• Ultrasonic– Sounds with frequencies that are higher than
20,000 Hz
• Infrasonic-– Sounds with frequencies that are lower than 20
Hz
Volume• Decibel (dB) - unit to express volume
• Exposure to sounds above 85 dB causes hearing loss
SIMSIM - dB
What is an Ultrasound?
Ultrasound Simulation
Beat Frequency• Two waves with similar frequencies alternate
constructive/destructive interference
• Causes sound to alternate loud and soft
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Beating Frequency (SIM1) (SIM2)
Beating Frequency Applet 2
Beating Frequency Applet 3
Sound from:
A stationary object
A moving object
(SIM1)(SIM2)
SIM – Doppler Effect LabeledSIM – Hear DopplerSIM – Doppler/hear police sirenSIM – Doppler/see police siren
Final Note:
Mechanical waves and
Electromagnetic Waves
are different!
Sources:
Bloomfield, How Things Work.Krauskopf & Beiser, The Physical Universe. 10th ed. Tillery, Physical Science.www.physicsclassroom.com
