38-41;Elasticity/Travelling waves/Wavelength/Doppler Effect/ Flashcards
elasticity
property of object that restores to its org dimensions after distorting froces are removed
EG spring/rubber band; when stretched will return to its og length = demonstrates elasticity
hooke’s law
linear relationship, deformation of elastic solid proportional to deforming force
periodic motion
motion which repeats itself at regular time intervals
characteristic of elastic objects moving under influence of Hooke’s forces
= when spring hung vertically w/ mass suspended = spring stretches until elastic restoring force is great enough to support weight
when mass pulled down and releases = oscillates up and down in simple harmonic motion = finally at rest until energy has been dissipated into U
amplitude of motion
max distance moved from equil point
resonant frequency
periodic motion occurring at one or more natural freq
determined by physical properties of system EG mass/lengt/stiffness
travelling waves
any part of elastic object disturbed to propagate to all parts of object
matter w/ definite equil state has a tendency to periodic motion, in extended body = periodic motion takes form of travelling wave
EG waves in a pond
transverse waves
particles of medium oscillate back and fourth perpendicular to direction of propagation of wave
EG waves in string, light/radio/x-ray waves
longitudinal waves
periodic motion of particles parallel to propagation direction
EG sound waves
speed of propagation
determined by the medium in which the wave is travelling, not freq/amplitude of wave
wavelength
shortest repeat distance for periodic wave
distance btw crest/compressions of spring
freq
no. of times a periodic function/vibration repeats in 1 sec
wave properties of sound
sound= travelling pressure wave, can be propagated though a material medium but cannot travel through vacuum
audible sound = 20-20000Hz
Ultrasound = f>20000Hz
infrasonic f<20Hz
sound originates when elastic object vibrates back and fourth rapidly = sends audible freq thru medium in which it vibrates
EG tuning a fork
wave properties of light
travelling wave consisting of propagating electric and magnetic fields
transverse wave v=2 x 10^8 m/s
infrared/uv = waves w/ freq below and above visible light
energy in waves
all travelling waves carry certain amount of energy that travels in ordered motion until finally dissipated into disordered motion IE internal energy
interference
addition of 2 or more waves that pass the same point in space
destructive Interference = waves from 2 diff sources meet w/ same amplitude = will cancel each other = leaves momentary flat spot
constructive interference = 2 wave crests coincide and add = produces larger crest
standing wave
interference btw reflected waves so will vibrate up and down in fixed segments = natural/resonant freq
doppler effect
EG when vehicle passes you, noticeable drop in pitch of sound of siren
Due to sound wave consisting of series of high and low pressure areas in air
v=345 m/s at T=20 C
generalised doppler equation
used when source or observer may be moving w/ respect to the medium
doppler shift
when sound source is stationary and observer is moving
DS of light freq = astronomers measure speed of recession of distant stars
DS of freq of microwave radiation = air traffic controllers measure speed of approaching aircraft
ultrasound uses
SONAR/SOund Navigation And Ranging
use of US echo for:
- observing blood flow through major arteries
= US from source transducer produces DS that echoes off moving RBC into arteries = doppler probe can locates constrictions of vascular system = identifies increase of speed of blood flow
-detecting foetal heart tones
= US waves directed at body = reflections at interface between diff tissues/fluids produces change of speed of sound = speed of sound depends on density = outlines produced due to density changes
