Unit 6 Vibrations and Waves Flashcards
Vibration
a back and forth motion about an equilibrium position
Periodic Motion
a repeated motion
-back and forth
-doesn’t stop at equilibrium
Hooke’s Law
Fs = -k /\x
Spring constant (k)
a measure of the stiffness of a spring (unit: N/m)
Simple Harmonic Motion
Any period motion or vibration that is the result of a restoring force that is directly proportional to the displacement
Pendulum
consists of a mass attached to a string
Amplitude (A)
the maximum displacement from equilibrium
Period (T)
the time it takes a complete cycle to occur
Frequency (f)
the number of cycles or vibrations per unit of time
units: Hertz
Frequency and Period are inverses so the formula is
f = 1/T
formula for period of a mass spring system
Ts = 2π√(m/k)
formula for period of a pendulum
Tp = 2π√(L/ag)
Wave
a disturbance that is transmitted progressively from one place to the next with no actual transport of matter
-a transfer of energy
-cannot exist in one place, but must extend from one place to another
Medium
a physical environment through which a wave can travel
-the particles in the medium move in vertical circles as the wave passes
The source of waves
The source of all waves is something that vibrates. The vibrating causes a disturbance in the medium that travels to the receiver
Crest
the high point on a wave
Trough
the low point on a wave
Wavelength (λ)
the distance between two adjacent similar points of a wave such as from crest to crest or trough to trough
Transverse Wave
a wave whose particles vibrate perpendicular to the direction the wave is traveling
(normal example wave)
Examples of Transverse Waves
stringed instruments, bridge cables, electromagnetic waves
Longitudinal Waves
a wave whose particles are parallel to the direction the wave is traveling
Examples of Longitudinal Waves
sound waves, pressure waves, density waves
Compression of a Longitudinal wave
the part where the wave is closest together (dar par in water waves
Rarefaction of a Longitudinal Wave
the most stretched out part of the wave (light part)
What does the speed of a wave depend on?
the medium through which it travels
Equation for speed of a wave
v = λf of v = λ / T
interference patterns
a regular arrangement of places where wave effects are increased, decreased,or neutralized
Constructive Interference
the crest of one wave overlaps the crest of another wave and their individual effects add together
-also known as reinforcement
Destructive Interference
the crest of one wave overlaps the trough of another wave and their individual effects are neutralized
-also known as cancellation
Standing Wave
a wave patter that results when two waves of the same frequency, wavelength, and amplitude travel in opposite directions and interfere
-a wave that appears to stay in one place and does not seem to move through the medium
Node
a stationary point on a standing wave
Antinode
the points on a standing wave with the highest amplitde
What creates standing waves?
interference.
a standing wave only forms if half a wavelength or a multiple of half a wavelength fits exactly into the length of the vibrating medium
Doppler Effect
as a wave approaches, an observer encounters waves with a higher frequency; as a wave source moves away, an observer encounters waves with a lower frequency
supersonic
faster than the speed of sound
Bow wave
occurs when a wave source moves faster than the waves it produces
-forms a v shape
-the faster the source, the narrower the wave
-2d wave
shock wave
occurs when an object moves faster than the speed of sound
-3d wave
sonic boom
a sharp crack hear when a shock wave behind a supersonic airplane reaches a listener
Sound
a longitudinal wave and form of energy that spreads out through space
Pitch
a measure of how high or low a sound is perceived, to be depending on the frequency of a sound wave
-high pitched sound = high vibration frequency
-low pitched sound = low vibration frequency
Infrasonic
sound waves with frequencies below 20 Hz
-too low for the human ear
Ultrasonic
sound waves with frequencies above 20,000 Hz
-to high for the human ear
characteristics of sound through different mediums
sound travels fastest in solids, then liquids, then gasses because of particle spacing.
-the speed of sound in a gas depends on temperature and mass.
-the speed of sound in a solid depends on elasticity
-sound can’t travel in a vacuum/space because it requires a medium to transmit.
Elasticity
the ability of a material to change shape in response to an applied force and then resume its initial shape once the disturbing force is removed
How is loudness measured
It is called sound intensity and it measured by an oscilloscope
- it is directly proportional to the square of the amplitude of the sound wave.
Natural Frequency
the frequency at which an object vibrates when it is disturbed
-depends on the elasticity
-minimum energy required to produce vibrations
Forced Vibration
occurs when an object is made to vibrate by another vibrating object that is near by
-causes resonance
Resonance
a phenomenon that occurs when the frequency of a vibration forced on an object matches the object’s natural frequency
-resonance occurs when there is enough force to pull it back to it’s starting position and enough energy to keep it vibration
-resonance creates standing waves at max amplitudes in 1/4 wavelength
constructive interference in a sound wave = (louder/quieter sound)
louder
destructive interference in a sound wave = (louder/quieter sound)
quieter
beat
a periodic variation in the loudness of sound
- occurs when two tones of slightly different frequencies are sounded together,
Photon
massless bundles of concentrated electromagnetic energy
-have no mass but still have momentum and they travel at the speed of light
Photoelectric Effect
the ejection of electrons from certain metals when light falls on them
Electromagnetic Wave
energy that is emitted by accelerating electric charge that travels in a wave that is partially electric and partially magnetic.
-fields are perpendicular to each other
-the waves don’t need mediums to travel
Electromagnetic Spectrum
consists of gamma rays, x-rays, ultraviolet, visible light, infrared waves, microwaves, and radio waves
-in order from highest to least frequency
What is the significance of ROY G BIV
Red has the longest light wavelength, green has a medium length light wavelength and violet has the shortest wavelength
speed of light (c)
in a vacuum/space, light travels at 299,920 km/s a year or 3 x 10^8 m/s
Light year
the distance light travels in a year
scattering
occurs when light bounces off an object in a variety of directions
-makes the sky blue
-used to track clouds and natural disasters
Transparent Materials
materials that light passes through whose atoms absorb that energy and immediately reemit it as light; no change in frequency
-ex: glass, water
Opaque Materials
materials that absorb light without being reemited and thus allow no light to to pass through them
Ray
a thin beam of light
Shadow
formed where light rays cannot reach
Umbra
total shadow
(dark part where all light is blocked)
Penumbra
Partial Shadow
(lighter part around the edges that experience some light)
Solar Eclipse
when the moon’s shadow falls on the earth
-the moon is in between Earth and the sun
Lunar Eclipse
an eclipse of the moon when the earth’s shadow falls on the moon
-the moon is being blocked by earth
Polarization
the alignment of electromagnetic waves in such a way that the vibrations of the electric fields of each wave are parallel to each other
-polarized light vibrates in only one direction while normal light vibrates in all directions
Spectrum
a spread of the colors of the rainbow
Primary Colors
Red, Blue, Green - mix to white
Reflection
the return of a wave back into it’s original medium
Law of Reflection
the angle of incidence (incoming light) = the angle of reflection
Diffuse Reflection
when incident light hits a rough surface and bounces in many different directions
Specular Reflection
when incident light hits a smooth surface and bounces in one direction
Refraction
the bending of a wave as it crosses the boundary between two mediums at an angle due to changes in wave speed
-makes things appear closer than they really are
speed of light in water
75% of the original speed of light
speed of light in glass
67% of the original speed of light
speed of light in diamond
40% of the original speed of light
Dispersion
the separation of light into colors according to their frequency
-involves reflection and refraction
-produces a rainbow
Diffraction
the bending and spreading of waves around an obstacle
-bending by means other than reflection or refraction
-think of the light expanding through a hole or slit
Diffraction Grating
has multiple closely spaced parallel slits which separate light into color by interference and cause iridescence.
Radiation
energy that travels and spreads out as it goes
Electron Volt (cV)
the amount of kinetic energy needed to move an electron through 1 volt of potential
In a mass spring system
as /\x increases,
A child is being pushed on a swing. The child’s natural frequency of swinging is once each for seconds. For maximum amplitude, the man should push at a rate of once each:
4 seconds, creating resonance
the reason that the sky is blue is that air molecules
scatter blue light in all directions
