Units 10-11 Flashcards
Mechanical waves
Waves that move through matter.
A “disturbance” with a repeating shape.
True or False: Mechanical waves are a disturbance
True
Why are waves called disturbances?
Waves cause a disturbance or a deviation in the equilibrium of the matter they are passing through.
What continues PROPOGATING waves?
Forces attempting to restore the medium to its equilibrium position.
Without restoring forces, there would be no waves.
How many types of mechanical waves are there?
2
What are the types of mechanical waves?
Longitudinal (compression)
Transverse (shear)
What is a longitudinal wave?
A wave that causes the molecules of the medium to vibrate in the SAME direction the wave is moving.
What is a transverse wave?
A wave that causes the molecules to vibrate at RIGHT ANGLES to the wave direction.
What is a compression wave?
A longitudinal wave driven by the force of pressure
What is a shear wave?
A transverse wave driven by shearing forces between molecules
What is a surface wave?
A wave that travels along the surface of a medium (like water)
True or False: Surface waves contain both longitudinal and transverse motions.
True
What kind of wave is light?
Transverse, but not shear
Example of compression wave
Sound
Why do shear waves ONLY propagate through solids?
Because when traveling through liquids, gases, and plasmas, the molecules are not rigidly bound to each other and drift away in the direction the force pushes on them.
Why do compression waves successfully pass through solids AND liquids, gases, and plasmas?
The molecules are not rigidly bound, but resist being compressed enough to provide a restoring force. They don’t drift (caused by shear forces).
What do restoring forces do?
Seek to restore equilibrium
Does the energy of the wave decrease or stay the same as it travels?
Decreases.
Crest
Places in waves of maximum forward OR upward displacement.
Upward for shear
Forward for compression
Trough
Places of maximum downward OR backward displacement.
Where are the equilibrium positions located between crests and troughs?
Halfway between them
How many properties define how particles vibrate back and forth between crest and trough?
4
What are the four properties of particle vibrations?
- Amplitude
- Wavelength
- Frequency
- Speed
Amplitude
The maximum distance a particle moves from its natural resting place.
ie. the distance between equilibrium and a crest or trough
True or False: High amplitude equals high energy
True
How does amplitude manifest in sound waves?
Loudness
Wavelength
The distance between successive repeating parts of a wave (like crests or troughs)
How does wavelength manifest in visible light?
Color
True or False: Red is a short wavelength and violet is a long wavelength
FALSE
Reverse
True or False: Longer wavelengths of sound waves produce lower tones.
True
Frequency
Measures the number of wave crests passing a particular point every second.
What is the unit of measurement for frequency?
Hertz
“oscillations per second”
How does frequency affect visible light?
It manifests as color. Red is low frequency, violet is high frequency
How does frequency manifest in audible sounds?
Higher frequencies produce higher tones, etc.
What is the range of sound frequency our ears are sensitive to?
20 to 20,000 hertz
Wave speed
The rate that the disturbance travels through the medium.
What does wave speed depend on?
The medium’s elastic properties, its density, and the type of wave going through it.
True or False: Compression waves travel faster than shear waves
True
True or False: Wave speed is INDEPENDENT of wavelength, frequency, or amplitude
True
A scream travels as fast as a whisper.
Wave speed formula
wave speed = frequency x wavelength
True or False: Wave length and frequency have an INVERSE relationship
True
True or False: It is ALWAYS true that high frequency corresponds to short wavelengths and low frequency corresponds to long wavelengths.
TRUE