Waves

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Waves

Doppler Effect

An example of this occurring is when a car honks while it moves at a fast speed past you; the honk will sound like it is changing pitch.

Doppler Effect: when a source of sound approaches an observer, the observed frequency of the sound increases; when the source moves away from an observer, the observed frequency of the sound decreases.

Waves at Media Boundaries:

Fundamental Frequency or First Harmonic (f0): the lowest frequency that can produce a standing wave in a given medium.

Antinode: in a standing wave, the location where the particles of the medium are moving with greatest speed; the amplitude will be twice the amplitude of the original wave.

Node: in a standing wave, the location where the particles of the medium are at rest.

Standing Wave: an interference pattern produced when incoming and reflected waves interfere with each other; the effect is a wave pattern that appears to be stationary.

Transmission: the motion of a wave through a medium, or motion of a wave from one medium to another medium.

Fixed-end Reflection: a reflection that occurs at a media boundary where one end of the medium is unable to vibrate; reflections are inverted.

Free-end Reflection: a reflection that occurs at a media boundary where the second medium is less dense than the first medium; reflections have an amplitude with the same orientation as the original wave.

Properties of Sound Waves:

Decibel (dB): the unit of sound level used to describe sound intensity level

Mach number (M): the ratio of the airspeed of an object to the local speed of sound.

(M) = the airspeed of the object divided by the local speed of sound.

The speed of sound is 331.4 m/s + (0.606 m/s/°C)T where T is the temperature in celsius.

Echo: the sound energy reflected off a surface back to the producer of the sound

-Sound waves are audible to humans between 20 Hz and 2 kHz. Sound waves < 20 Hz are called infrasonic waves. Sound waves > 2 kHz are called ultrasonic waves.

Types of Mechanical Waves:

-Many wave motions in nature are a combination of longitudinal and transverse motion.

-Sound, an important example of a longitudinal wave, is a form of energy produced by rapidly vibrating objects.

-In a fluid, longitudinal waves transfer energy through regions of higher and lower pressure. These regions are called compressions and rarefactions, respectively.

-In longitudinal waves, the particles of the medium move parallel to thedirection of the flow of energy.

-In transverse waves, the particles of the medium move perpendicular to thedirection of the flow of energy.

Beats:

-Many musical instruments can be tuned using beats.

Beat Frequency: the frequency of beats produced by the interference of two waves with slightly different frequencies; equal to the difference in the frequencies of the interfering waves.

Beats: periodic change in sound intensity caused by the interference between two nearly identical sound waves.

Interference of Waves:

Subtopic

Destructive Interference: the process of forming a wave with a smaller amplitude when two or more waves combine.

Constructive Interference: the process of forming a wave with a larger amplitude when two or more waves combine.

Principle of Superposition: at any point the amplitude of two interfering waves is the sum of the amplitudes of the individual waves.

Interference: the process of generating a new wave when two or more waves meet.

Characteristics of Waves:

Simple Harmonic Motion: any motion that repeats itself at regular intervals

Wave speed (v): the rate at which a wave is travelling through a medium; also a measure of how fast the energy in the wave is moving

Factors that affect wave speed and how to calculate them.

Linear Density (m):the mass per unit distance of a string; units are kilograms per metre (kg/m)

Equation to calculate wave speed.

Period (T): the time for a wave to complete one cycle, usually in seconds.

Frequency (f): the number of complete cycles that occur in unit time, usually 1 s; measured in hertz (Hz)

Phase shift: the shift of an entire wave across the x-axis.

Trough: the minimum point of a transverse wave.

Crest: the maximum point of a transverse wave

Wave forms: the shape of a wave when graphed

Vibrations:

-The speed of a wave and the distance it can travel depend on the composition of the medium. A rigid medium allows a wave to travel longer and faster than a less rigid medium. A less rigid medium disperses more energy, thus reducing the speed and distance that a wave can travel.

-the particles of an elastic medium return to their original location after a wave passes through.

-a medium is a material that allows the transmission of energy due to vibrations; can be a solid, liquid, or gas.

-a mechanical wave is a transfer of energy through a medium by particle vibration. Particle vibration is caused by a disturbance to the medium (

-all vibrations need a medium to transfer waves

-a vibration is the cyclical motion of an object around an equilibrium point.