Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
VIBRATIONS AND WAVES Equilibrium and Stability ● Equilibrium – ● An arrangement which produces zero net force Stability – – – Forces can push a system toward or away from equilibrium Forces push toward a stable equilibrium Forces push away from an unstable equilibrium Stable equilibrium leads to vibrations: System “wiggles” around the equilibrium state Unstable equilibrium Mass-Spring Vibrations ● Mass attached to spring → stable equilibrium – – ● Frequency – – – ● Produces a vibration! Called “Simple Harmonic Motion” (SHM) The number of vibrations per second Measured in units called Hertz (Hz) “Period” = seconds per vibration Amplitude – – “Size” of vibration → how far away from equilibrium? Bigger amplitude → more energy in vibration Waves ● Substances have a “stable equilibrium state” – – – ● Uniform pressure everywhere throughout the substance “Atomic springs” are at their equilibrium length Can make a wave by disturbing the equilibrium Physics definition of a wave – – – A vibration which moves through a substance Each individual molecule undergoes SHM... ...but energy moves from molecule to molecule Molecule motion Wave motion Wavelength ● Vibrational motion repeats itself after one period – ● Notice that the wave is moving during this time Wavelength – Distance moved by a wave during one period Wavelength is symbolized by the Greek letter λ λ Wave Speed wavelength Wave Speed = = wavelength × frequency period ● Calculating wave speed – ● Wave speed depends on the substance – – ● Wave moves one wavelength every period Called the “medium” of the wave Wave speed is a constant in a specific medium So if the frequency of a wave increases... – ...Wavelength must decrease! Common Wave Examples ● Sound waves → produced by: – – ● Waves on a string: – ● String under tension → “shaking” it produces a wave Water surface waves – ● Quick changes in pressure Vibrating objects Produced by disturbing a flat water surface Electromagnetic waves – Produced by “wiggling” charged particles Transverse vs. Longitudinal Waves ● Two different motions to describe in a wave: – – ● Transverse waves → Two motions are perpendicular – ● Waves on a string, water surface waves Longitudinal waves → Two motions are parallel – ● Motion of the wave's energy Motion of individual molecules of the wave Sound waves Waves can have both transverse and longitudinal motion – Earthquakes, ocean waves produce “rolling” motion Doppler Effect ● If a wave source moves: – – ● Source moving toward listener: – ● Wavelength and frequency of the wave are affected During one period, the location of the source changes Wavelength is decreased; frequency is increased Source moving away from listener: – Wavelength is increased; frequency is decreased Doppler Effect Example: Hubble Expansion ● Stars contain the same elements as Earth – ● Astronomers do see this light... – ● We expect to see light of specific frequencies from them But the frequencies are shifted! Using Doppler → calculate the star's velocity – – – Edwin Hubble: observed many stars in early 20th century Found that almost all stars move away from Earth Therefore the universe is expanding! Shock Waves ● Source moves through medium → Doppler effect – – – What if a source moves near the speed of sound? Waves start to “overlap” and produce a shock wave Shock waves take up small volume but have large energy