Upload
gerald-wiggins
View
216
Download
0
Tags:
Embed Size (px)
Citation preview
WavesWaves
What is a Wave?What is a Wave?
• A wave is an energy vibration that usually takes place in matter
• Key word: vibration. Waves repeat
• A single “wave” is called a pulse
Wave TypesWave Types
• Transverse Waves vibrate at a right angle to their direction of motion
• Examples: Light, ocean waves, waves on a rope
• Longitudinal Waves vibrate in the direction of motion
• Examples: Sound, P-Waves, “Slinky” Waves
Wave PropertiesWave Properties
• We use four different characteristics to talk about waves: frequency, wavelength, amplitude, period, and speed
• Wavelength is the distance between identical parts of a wave (crestcrest, troughtrough)
• Amplitude is half the wave’s total height, or the distance between the crest and the rest position
Wave TimeWave Time
• A wave’s period is the time it takes for one vibration to occur
• If you divide wavelength by time, you get a wave’s speed (speed = distance/time)
FrequencyFrequency
• A wave’s frequency tells us how often waves occur (2 waves a second, 4 waves a second, etc)
• The units of frequency are Hertz, or Hz
• 1 Hz = 1 wave/second
• Frequency = 1/period
Source or Medium Dependence?Source or Medium Dependence?
• Amplitude?– Source Energy
• Period– Source
• Speed– Medium
• Wavelength– Medium/Source
Some WavelengthsSome Wavelengths
• Microwaves: .03 m
• Radio Waves: 10 m
• Ocean Waves: 200 m
• Tsunami: 11,000 m
• 200,000 m
Two ViewsTwo Views
• Position/Time View– We focus on how one point on the wave
evolves in time
• Snapshot View– We focus on how the wave evolves in multiple
dimension
Time ViewTime View
• Which wave properties can we deduce from this graph?
SnapshotSnapshot
• What can we deduce from this graph?
Interference with Standing WavesInterference with Standing Waves
ResonanceResonance
• Questions of Interest:
• Can you break a wine glass with sound?
• Why did the Tacoma Narrows bridge collapse?
Forced VibrationsForced Vibrations
• Vibrating an object at a specific frequency
• Think back to the lab from last week (part C)
• Forced vibrations can create either organized or unorganized patterns
• On what does the pattern’s organization depend?
Natural FrequencyNatural Frequency
• Most objects (media) have so called natural frequencies
• If we vibrate an object at one or more of its natural frequencies, something interesting occurs
ResonanceResonance
• When a source vibrates an object at its natural frequency, we call it resonance
• You can create large amplitudes with fairly small input
Other Examples?Other Examples?
• Swing sets
• Singing in the shower
• Tuning fork
• Standing waves on spring
Raising the stakesRaising the stakes
• If you continue vibrating something at its resonance frequency, the amplitude of the vibration increases
Shattering a Wine Glass?Shattering a Wine Glass?