Vibrations and Waves Flashcards
Vibration
The repeated motion of a particle in a medium.
Cycle
One complete vibration (oscillation)
Wave
A disturbance that transfers energy over a distance
What are the 3 types of vibrations?
Transverse Vibration, Longitudinal Vibration, Torsional Vibration
Transverse Vibration
Object vibrates perpendicular to its axis. Ex: kid on swing, guitar string.
Longitudinal Vibration
Object vibrates parallel to the axis. Ex: baby jumper, shocks on car.
Torsional Vibration
Object twists back and forth around its axis.
Amplitude
Distance from equilibrium position to max displacement
Frequency
of cycles completed per unit time ( f = #cyc / total t )
Period
The time to complete one full cycle. ( T = total t / #cyc )
What is Periodic Motion?
Motion that occurs when the oscillation/vibration of an object repeats (exactly) in equal time intervals.
What is the universal wave equation?
V=fλ
What does a reflected pulse from a fixed end look like?
reflected and inverted
What does a reflected pulse from a free end look like?
reflected
What is the Principle of Superposition?
At any point on the medium the resulting amplitude is the algebraic sum of the two interfering amplitudes.
Define Wave
A periodic disturbance which transfers energy over a distance
What are the characteristics of a wave?
Crest: The region where the displacement is positive
Trough: The region where the displacement is negative
Amplitude (A): The distance above/below its equilibrium position to max displacement
Wavelength (λ): The distance between any consecutive points on the waves which are in phase (crest-crest)
Does amplitude of a pulse affect its speed?
No
Which is faster, the initial pulse or reflected pulse?
They should be equal.
How do you make a wave go faster?
More force
What happens to wavelength if frequency of vibrations is increased?
As frequency increases, wavelength decreases
What is wave interference?
When two waves simultaneously act on the same particles in a given medium
What are the two types of interference?
Destructive and Constructive interference
Destructive Interference
The two amplitudes cause the waves to cancel out / reduce amplitude
Constructive Interference
When two amplitudes build up creating a larger amplitude
Node
Points at rest on a standing wave
Anti node
Points between nodes which experience maximum displacement
Why wont every frequency create a standing wave?
The λ and velocity must “fit” on the spring
What happens when a wave moves to a slower medium?
If velocity decreases, λ decreases. The heavy/slow medium acts like a fixed end causing reflection to be inverted
Resonant Frequency
The natural frequency at which an object vibrates best
Mechanical Resonance
The transfer of energy from one object to another with the same natural frequency
Sound Waves
A form of energy produced by a rapidly vibrating object. They are longitudinal vibrations which require a medium.
Human Audible Range
20 Hz to 20 000 Hz
Sound Intensity
Energy per unit area at a particular point per second measured in W/m^2
Sound Intensity Level
Each increase by 10dB causes 10x as intense sound. Every 3dB increase doubles sound intensity.
Hearing Loss/Protection
85dB = 8h max exposure. As the intensity doubles (safe) exposure time is cut in half.
Resonance in closed air columns
1st resonant length = 1/4λ, 2nd r.l. = 3/4λ, 3rd r.l. = 5/4λ
Resonance in open air columns
1st resonant length = 1/2λ, 2nd = 1λ, 3rd = 3/2λ
Doppler effect
Moving towards = shorter λ, (Vw/Vw-Vs), fd > fs
Moving away = longer λ, (Vw/Vw+Vs), fd
What are: (Vw), (Vs), (fs), (fd)
Vw: speed of wave, Vs: speed of source, fs: frequency of source, fd: observed (Doppler) frequency
The Sound Barrier
As object velocity gets close to speed of sound, the highly compressed sound waves in front pile up and make it hard to break through
Super-Sonic Speed
At speeds faster than the speed of sound, sound waves form a cone, trailing off behind (plane). Because the waves line up along the edges of the cone, we hear a sharp “crack” or sonic boom
Mach Speed
Mach # = speed of object / speed of sound
Beats
Two nearly identical sounds are played simultaneously and will both act constructively and destructively, producing alternating loud and quiet sound waves (beats).
Beat frequency
f(beat) = I f2-f1 I
