Waves and Sound. 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?
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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.
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.
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 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
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?
