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## Waves and Sound

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**Intro**A. Pick up your notes and worksheet packets B. Write the following questions on a blank piece of paper (don’t answer yet) 1. What is the difference between a mechanical and electromagnetic wave? 2. What is the difference between a transverse and longitudinal wave? 3. What do all waves transfer? 4. What don’t waves transfer?**Waves**• Are disturbances that move through an empty space or through medium (material) • Waves transfer energywithout transferring matter. • Particles of medium move in simple harmonic motion Mechanical: Through a medium Electromagnetic: Through empty space**Mechanical wave:**• Caused by a disturbed medium and move by action reaction of particles • ex: water wave, sound • A medium is matter particles like gas (ex. air), liquid (ex. Water), and solid (ex. earth) Two types of mechanical waves that require a medium Transverse Wave Longitudinal Wave**Electromagnetic wave:**• Move through empty space (no medium) • Created by moving electrons • Ex. radio waves, microwaves, light • SOL= 3.0 x 10 8 m/s Types Electromagnetic Waves Through empty space**In order to start and transmit a wave, a source of**disturbance (vibration) and a disturbed medium are required. • Mechanical caused by vibrating particles • Like seen here • Electromagnetic by vibrating electrons**Damping:**• A decrease in the amplitude of a wave • Caused by energy loss or the spreading out of the wave over a larger area.**Wave pulse is a single wave disturbance**• Wave train (continuous wave) - is a series of pulses at intervals**Transverse**Longitudinal Section 2: Types of Mechanical Waves**Transverse Wave:**• Wave particles move perpendicular to the direction the wave travels • Ex. vibrating string of a musical instrument Perpendicular to the direction of travel Direction of travel**Parts of a transverse wave**Crest Wavelength (ג) amplitude Equilibrium Position Wavelength (ג) amplitude Wavelength (ג) Trough**Crest- highest point on a transverse wave**• Trough- lowest point on a transverse wave • Equilibrium position- center around which simple harmonic motion occurs • Amplitude- from the equilibrium position to the crest or trough**Longitudinal Wave:**• Particles vibrate parallel to the direction the wave travels • ex. sound wave Direction of travel Particles vibrate parallel to the direction of travel**Parts of a Longitudinal Wave:**• Compression- point where the particles are closest together • Rarefaction- point where the particles are furthest apart Rarefaction Compression**Intro Questions**• What do all waves transfer? • What don’t waves transfer? • What starts a wave? Pick between the following choices and answer this correctly: 4. Sound is a (mechanical or electromagnetic) (transverse or longitudinal) wave.**Section 3: Relationship between Wavelength, Frequency and**Wave Speed**velocity ( v ): speed of the wave.**• unit: m/s (meter/second) • frequency ( f ): vibrations per second of the wave • unit: Hz (hertz) • wavelength ( ג ): length of one wave pulse • unit: m (meter)**d**t V= ___ Lets revisit our old equation What is the velocity of an object that moves 25 meters in 3 seconds?**d**t V= ___ Lets revisit our old equation What is the velocity of an object that moves 25 meters in 3 seconds?**d**t V= ___ Now lets look at the new equation you can use as well. new old Example what is the velocity of a wave that has a frequency of 3Hz and a wavelength of 5m?**d**t V= ___ Now lets look at the new equation you can use as well new old**d**t V= ___ Now lets look at the new equation you can use as well new old**d**t V= ___ Now lets look at the new equation you can use as well new old**d**t V= ___ Now lets look at the new equation you can use as well new old**Relationship between frequency and wavelength.**• Wavelength and frequency are inversely related • As frequency goes up the wavelength gets shorter (assuming no change in velocity) Click for animation**Period (T) vs. Frequency (f)**• Period (T) – seconds for one cycle • (unit s) • Frequency (f) – cycles for one second • (unit Hz) • If you know one you can solve for the other**Example 1Wave Math**The frequency of a wave is 560 Hz. What is its period?**Example 2Wave Math**A girl floats in the ocean and watches 12 wave crests pass her in 46 s. Calculate the wave: a) frequency b) period**A girl floats in the ocean and watches 12 wave crests pass**her in 46 s. Calculate the wave: a) frequency b) period**Example 3Wave Math**The period of a wave is 0.044s. How many cycles will the energy source make in 22s? cycles second**The period of a wave is 0.044s. How many cycles will the**energy source make in 22s?**Example 4Wave Math**A distance of 0.33 m separates a wave crest from the adjacent trough, and the vertical distance from the top of a crest to the bottom of a trough is 0.24m. A. What is the wavelength? B. What is the amplitude? 0.33m 0.24m**Example 4Wave Math**A distance of 0.33 m separates a wave crest from the adjacent trough, and the vertical distance from the top of a crest to the bottom of a trough is 0.24m. A. What is the wavelength? B. What is the amplitude? 0.33m 0.66m**Example 4Wave Math**A distance of 0.33 m separates a wave crest from the adjacent trough, and the vertical distance from the top of a crest to the bottom of a trough is 0.24m. A. What is the wavelength? B. What is the amplitude? 0.12m 0.24m**Example 5Wave Math**What is the speed of a 256 Hz sound with a wavelength of 1.35 m?**Example 5Wave Math**What is the speed of a 256 Hz sound with a wavelength of 1.35 m?**Example 6Wave Math**You dip your finger into a pan of water 14 times in 11s, producing wave crests separated by 0.16 m. A. What is the frequency? B. What is the period? C. What is the velocity?**Example 6Wave Math**You dip your finger into a pan of water 14 times in 11s, producing wave crests separated by 0.16 m. A. what is the frequency B. What is the period C. Velocity**Assignment to work on:**CP • Worksheet Packet Section 3 Honors • Worksheet Packet Section 3 • Book Problems 4,5,6 pg 486-487**Pendulum Lab day: Your into is to read over your lab; I will**ask you if there are any questions soon Length (L) Amplitude (A) Equilibrium Position**Pendulum Lab day**One complete cycle**Intro after pendulum labAll labs are due today: Turn them in**on my desk • Your pendulum makes 5 complete cycles in 10 seconds. • What is the pendulums frequency? • What is the pendulums period? • What is the definition of frequency (can be in equation form) • When you increase the length of the pendulum string, what happens to frequency?**Pendulum- a weight on a string that moves in simple harmonic**motion (swings back and forth). • Movement from a to c and back to a is one complete cycle or vibration This is the equilibrium position. decelerating accelerating**Simple harmonic motion- vibration about an equilibrium**position • Constant back and forth motion over the same path. • 15º is the maximum angle for a pendulum to have simple harmonic motion where our equations work**Masses do not effect the period in simple harmonic motion.**• What effects the period: • L – length of the string • g – acceleration due to gravity