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Waves
Transferring Energy
Waves: traveling disturbance that carries energy from one place to
another
Waves travel through water, but they do not carry the water (or the duck) with them.
What causes waves?
• Vibration: repeated motion starting waves; how waves get their energy
Medium
• Material through which waves travel
Mechanical Waves
• Must have a medium to travel– Examples: ocean waves, sound waves
• Bell jar example
Electromagnetic waves
• Need no medium to travel– Heat waves (radiation)
– Light waves
Transverse waves: move the medium at right angles to the
direction in which the waves travel
vibrationDirection of travel
Longitudinal: waves move the medium parallel to the
direction in which the waves travel.
Sound Waves
Direction of wave travel
Sound waves are longitudinal waves
Wavelength
• The distance between a given point on a wave to the same point on the next wave.
• Most commonly measured from the center of one crest to the center of the next crest.
wavelengthcrest
trough
normal
am
plitu
de
Amplitude
• Measured from the crest to the wave normal (wave “at rest”).
• Amplitude is the “power” of the wave
wavelengthcrest
trough
normal
am
plitu
de
Frequency
• The number of waves that pass a certain point in one second.
• Besides cycles per second, many times frequency is measured in Hertz (Hz). One Hertz is equal to one cycle per second
Which wave has the longer
wavelength?
Which wave has the higher
frequency?
Which wave has the longer
wavelength?
Which wave has the higher
frequency?
•Wavelength and frequency have an inverse relationship.
•As wavelength increases, frequency decreases.
•Brainpop on Waves
Speed of Waves
Velocity = frequency x wavelength
v = f λ• v = velocity
• f = frequency
• λ = wavelength
Speed of waves practice
• A middle C note has a wavelength of 1.34 meters. Its frequency is 256 Hz. What is the speed of this sound?
• Formula:
• Substitutions:
• Answer:
• The approximate outdoor temperature can be calculated by the number of times a cricket chirps per minute. Sound travels at the same speed (343 m/s) at sea level under the same atmospheric conditions (humidity, temperature, etc.). If a cricket’s chirp has a frequency of 180 Hertz, what is the wavelength of the sound?
• Formula: velocity = frequency x wavelength
• Substitutions:
• Answer:
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