Waves and Sound 2024 PDF

Waves & Sound Characteristics of Waves Water waves, microwaves, sound waves, and radio waves are all types of waves that transfer energy from one place to another. Waves-rhythmic disturbances that carry energy through matter or space EX: Water waves transfer energy through the water & e...

Waves & Sound Characteristics of Waves Water waves, microwaves, sound waves, and radio waves are all types of waves that transfer energy from one place to another. Waves-rhythmic disturbances that carry energy through matter or space EX: Water waves transfer energy through the water & earthquakes transfer energy through Earth Characteristics of Waves Both water waves and earthquakes travel through a medium. Medium-a material through which a wave transfers energy—can be a solid, liquid, or gas Waves that require a medium are mechanical waves  Electromagnetic waves Electromagnetic waves, such as light, do NOT need a medium to transfer the energy they carry  Types of Waves Transverse waves- the medium moves at right angles to the direction the wave travels EX: Water waves, light waves  Compressional (Longitudinal) Waves Compression wave-matter vibrates in the same direction as the wave travels (the medium is displaced in the same direction as the energy is moving) EX: Sound waves, Ultrasound  Measuring Transverse Waves Crest-highest points on a wave Trough-lowest points on a wave Wavelength-the distance between a point on one wave and the identical point on the next wave (distance from crest to crest) Measuring Transverse Waves Amplitude-the distance from the crest of a wave to the rest position of the medium Amplitude corresponds to the amount of energy carried by the wave Large energy --🡪 large height (amplitude) Small energy 🡪 small height (amplitude)  Wave Frequency Frequency-the number of wave crests that pass one place each second Frequency is expressed in hertz (Hz) 1 Hz = 1 wave per second  Wave Frequency As frequency (the # of waves that pass one place each second) INCREASES, the wavelength (distance from one point on a wave to the identical point on the next wave) DECREASES.  Diagram These two waves have the same frequency but different amplitudes These two waves have the same amplitude but different frequencies.  Wave Velocity Wave velocity (υ) describes how fast a wave moves forward Wave velocity (υ) can be determined by multiplying the wavelength and frequency. Wavelength is represented by the Greek letter lambda, (λ). Calculating the Velocity of a Wave  Calculating the Velocity of a Wave: Example A wave is generated in a wave pool at a water amusement park. The wavelength is 3.2 m. The frequency of the wave is 0.60 Hz. What is the velocity of the wave?  ANSWER Wavelength (λ) = 3.2 m Frequency (f) = 0.60 Hz Velocity (ν) = ? ν = λ x f ν = 3.2 m x 0.60 Hz = 1.92 m/s  Sound Waves Molecules in the air vibrate about some average position creating the compressions and rarefactions. We call the frequency of sound the pitch. The greater the frequency, the higher the pitch.  Pitch Bats interpret sounds surrounding them using their ears, and emit ultrasonic sounds of such high frequencies, that a human ear can't even hear them. They use these sounds to both orient within the space, hunt and communicate with each other. Elephants communicate with low-frequency rumbles, called infrasounds, that can travel more than a mile.  Doppler Effect An increase (or decrease) in the frequency of sound, light, or other waves as the source and observer move toward (or away from) each other. The effect causes the sudden change in pitch noticeable in a passing siren. Sound Waves  Speed of Sound Depends on the material of the vibrating medium Sound can vibrate water, wood (speakers, pianos), metal, plastic, etc. Speed of sound in dry air is 330 m/s at 0o C Faster in warm air, slower in cold Water 4 times faster than air, steel 15 times faster  Wave Reflection When a sound wave reflects (bounces off of) from a surface we generate an echo Wave reflection from surfaces depends on the characteristics of the surface Smooth hard surfaces reflect best Rough soft surfaces reflect poorly Energy not reflected is absorbed or transmitted through the material  Wave Reflection Think of arrows pointing in the direction of the wave motion We can trace the path of these arrows Law of Reflection states that the angle of incidence equals Wave Reflection Acoustics is the study of sound. Room design is very important for concert hall, meeting room etc.. Some reflections help with sound quality. Too many reflections can cause sounds to be distorted. https://www.youtube.c om/watch?v=bSlHewU 0hfQ  Wave Refraction If there is a change in the characteristics (density, temp.) of a medium, waves are bent. Ex. traveling from air to water This occurs because different parts of the wave front travel at different speeds Think of a marching around a curved track The inside people have to move more slowly than the outside people to keep the lines straight Wave Refraction  Wave Reflection & Refraction The combination of reflection and refraction enables imaging Examples: Ultrasonic medical imaging Naval SONAR for detecting submarines Bats catching mosquitoes  Natural Frequencies A stringed instrument, such as a guitar, generates a sound when you pluck the string. Waves are created on the attached strings that reflect back and forth. A guitar string stretched across the guitar vibrates at its natural frequency. The vibration of the guitar string on a guitar and the air inside is called a forced vibration, and this makes the sound of the string louder.  Resonance When the forced vibration matches a natural frequency we get a “resonance” condition Resonance describes the phenomenon of increased amplitude that occurs when the frequency of a periodically applied force is equal or close to a natural frequency of the system on which it acts.  Resonance Think about a swing on a playground You go higher when you pump the swing at its natural vibration frequency Famous Tacoma Narrows bridge collapse https://www.youtube.com/watch?v=y0xohjV7 Avo Can marching soldiers bring down a bridge? If their frequency is closely matched to the bridge’s natural frequency, the soldiers’ rhythmic marching will amplify the vibrational frequency of the bridge. If the mechanical resonance is strong enough, the bridge can vibrate until it collapses from the movement. So, soldiers are told to break step with each other when crossing a bridge.  Noise vs. Music? The most common kind of sound is noise, which has no set pattern and no definite pitch. White noise-when all the frequencies of noise are present in equal amplitude White noise has been found to have a relaxing effect on people. Music to Your Ears Music-is created using specific pitches (related to frequency) and sound quality and by following a regular pattern.  Musical Sounds A note of the same pitch & loudness on a violin and on a piano wouldn’t sound the same. These instruments have a different quality of sound. Sound quality-describes the differences among sounds of the same pitch & loudness Distinct sounds from instruments are produced by different combinations of wave frequencies.  Acoustics Reverberation-the effect produced by many reflections of sound Acoustics-the study of sound Concert halls and theaters are designed by acoustical engineers to provide the audience with the best sound. Soft, porous materials and certain room shapes can reduce excess reverberations.  Interference Interference-the ability of 2 or more waves to combine and form a new wave Musicians in a band play the same note at the same time so their compressions overlap to form a greater compression. As a result, the music sounds LOUDER.  Interference Constructive interference occurs when the compressions of different waves arrive at the same place at the same time. Destructive interference is when the compression of one wave arrives with the rarefaction of another wave. They cancel each other and decrease loudness.