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Waves, Optics. Waves, Vibrations, Frequency. 1. Why does sound transfer easier through a solid? (use the word energy) 2. Waves, Vibrations, Frequency. Where have you seen waves before?. Objectives. Describe what a wave is Know where waves come from
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Waves, Optics Waves, Vibrations, Frequency
1. Why does sound transfer easier through a solid? (use the word energy) • 2.
Waves, Vibrations, Frequency • Where have you seen waves before?
Objectives • Describe what a wave is • Know where waves come from • Name and describe features of the two main wave types (transverse and longitudinal) • Note the different types of waves • Be able to calculate Frequency and Period of a vibration
If you scream in space does it make a sound? • If a tree falls in the forest and no one is there, does it make a sound?
Sound sensation produced by stimulation of the organs of hearing by vibrations transmitted through the air or other medium.
Waves • Waves transfer energy from one place to another through a medium • Although the waves (and thus the energy) is moving the medium does not
Waves http://www.history.com/videos/tacoma-narrows-bridge-collapses#tacoma-narrows-bridge-collapses
Waves Wave Types: • Mechanical (through media) • Ocean waves • Sound Waves • Flapping Flag • Electromagnetic (through space) • Light • X-ray • Ultraviolet • Infrared • Radio waves • Microwaves
Waves Waves travel in 2 ways: 1. Transverse: • Black = Wave direction • Red = Particle direction • Wave direction is perpendicular to particle direction • Deep ocean wave, guitar string
Waves Waves travel in 2 ways: 2. Longitudinal: • Black = Wave direction • Red = Particle direction • Wave direction is parallel to particle direction • Sound, deep earthquake
Waves Surface Waves: • When a water wave is near the surface we get both Longitudinal and Transverse waves together
Measuring Vibrations • All waves are caused by vibrations • Frequency = vibrations / second • Frequency = cycles / second • Frequency is measured in Hertz (Hz) • 1 Hz = 1 cycle / second
Cycle • 1 cycle = the time it takes to go from here • To here • And then back again
Frequency • HSBC Pendulum
Period • Period is the amount of time for a single vibration to occur. • Period = 1/frequency • Period is measured in seconds
Summary • A wave transfers energy through a medium • Waves originate from a vibrating source • Frequency (Hz) = cycles / time (s) • Period (s) = 1 / Frequency (Hz) • Transverse waves – Wave direction is perpendicular (ḻ) to particle direction • Longitudinal waves – Wave direction is parallel (ǁ) to particle direction
1. A boat bobs up and down 20 times every minute, what is its frequency? • 2. What is the boat’s period
Practice Questions 1. A boat bobs up and down 20 times every minute, what is its frequency? • f = cycles / time = 20 / 60s = 0.3Hz 2. What is the boat’s period? • t = 1 / f = 1 / 0.33Hz = 3s
Homework • Heath - Physics Pg. 371: 1-6
1. What variable are you testing in your pendulum experiment? • 2. Create a diagram of a pendulum showing when it reaches maximum potential energy and maximum kinetic energy
What does the period of a pendulum depend on? • Here is the equation for a pendulum, solve for g. • Due today – Claim evidence and reasoning write up for the pendulum.
For the pendulum experiment is time the dependent or indepedent variable? • Which variable is time usually? (heart rate versus time) • Why
The speed of sound is 761.2 mph. How far away is lightning if you see the lightning then hear it 3 seconds later? • Who hears the sonic boom first?
1. Compare and contract a transverse wave and on longitudinal wave. • 2. 4 waves past by in 2 seconds that have a wavelength of 3 meters, find the • A. frequecy • B. period • C. velocity
Frequency = 1 / period • V= λ* f • Wave speed = wavelength * frequency
Warm up see hand out • Explain why you hear a beat when you hit two tuning forks of slightly different frequency
Doppler effect – apparent change in frequency causes by a moving object • -as an object approaches the frequency increases • - as an object moves away the frequency decreases • See doppler applet
Doppler effect • http://www.loncapa.org/~mmp/applist/doppler/d.htm
1. A sound wave is a pressure wave; regions of high (compressions) and low pressure (rarefactions) are established as the result of the vibrations of the sound source. These compressions and rarefactions result because sound • a. is more dense than air and thus has more inertia, causing the bunching up of sound. • b. waves have a speed which is dependent only upon the properties of the medium. • c. is like all waves; it is able to bend into the regions of space behind obstacles. • d. is able to reflect off fixed ends and interfere with incident waves • e. vibrates longitudinally; the longitudinal movement of air produces pressure fluctuations
Since the particles of the medium vibrate in a longitudinal fashion, compressions and rarefactions are created Compression – high pressure Rarefaction – low pressure
26.2Sound in Air • Opening and closing a door produces compressions and rarefactions. • When the door is opened, a compression travels across the room. • When the door is closed, a rarefaction travels across the room.
Pitch – what we hear (depends on frequency) • Below 20 hertz – infrasonic • Above 20,000 hertz -
26.1The Origin of Sound All sounds originate in the vibrations of material objects.
26.2Sound in Air Clap your hands and you produce a sound pulse that goes out in all directions. Each particle moves back and forth along the direction of motion of the expanding wave.
What does the speed of a wave depend on? • What is the relationship between frequency, wavelength, and wave speed?
26.3Media That Transmit Sound Most sounds you hear are transmitted through the air. Put your ear to a metal fence and have a friend tap it far away. Sound is transmitted louder and faster by the metal than by the air. Click two rocks together underwater while your ear is submerged. You’ll hear the clicking sound very clearly. Solids and liquids are generally good conductors of sound.
26.4Speed of Sound The speed of sound in a gas depends on the temperature of the gas and the mass of the particles in the gas. The speed of sound in a material depends on the material’s elasticity.
26.4Speed of Sound The speed of sound in dry air at 0°C is about 330 meters per second, or about 1200 kilometers per hour. This is about one-millionth the speed of light. Increased temperatures increase this speed slightly—faster-moving molecules bump into each other more often. For each degree increase in air temperature above 0°C, the speed of sound in air increases by about 0.60 m/s.
26.4Speed of Sound • The speed of sound in a solid material depends not on the material’s density, but on its elasticity. Elasticity is the ability of a material to change shape in response to an applied force, and then resume its initial shape. • Steel is very elastic. • Putty is inelastic. • Sound travels about 15 times faster in steel than in air, and about four times faster in water than in air.
26.5Loudness • Starting with zero at the threshold normal hearing, an increase of each 10 dB means that sound intensity increases by a factor of 10. • A sound of 10 dB is 10 times as intense as sound of 0 dB. • 20 dB is not twice but 10 times as intense as 10 dB, or 100 times as intense as the threshold of hearing. • A 60-dB sound is 100 times as intense as a 40-dB sound.
Natural frequency - - natural frequency at which an object vibrate – springiness • Drop a wrench and a baseball bat on the floor, and you hear distinctly different sounds. • Objects vibrate differently when they strike the floor. • Resonance- increase in amplitude when a frequency of a vibration reaches the natural frequency
26.6Natural Frequency Drop a wrench and a baseball bat on the floor, and you hear distinctly different sounds. Objects vibrate differently when they strike the floor. We speak of an object’s natural frequency, the frequency at which an object vibrates when it is disturbed.
26.6Natural Frequency Most things—planets, atoms, and almost everything in between—have a springiness and vibrate at one or more natural frequencies. A natural frequency is one at which minimum energy is required to produce forced vibrations and the least amount of energy is required to continue this vibration.
