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PHYSICS Mr. BALDWIN WAVES 14-Jan-14

PHYSICS Mr. BALDWIN WAVES 14-Jan-14. AIM: What is periodic or harmonic motion? DO NOW A mass is attached to a spring on a horizontal frictionless surface. The system is then compressed and released. Describe the motion of the mass.

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PHYSICS Mr. BALDWIN WAVES 14-Jan-14

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  1. PHYSICS Mr. BALDWIN WAVES 14-Jan-14 AIM: What is periodic or harmonic motion? DO NOW • A mass is attached to a spring on a horizontal frictionless surface. The system is then compressed and released. Describe the motion of the mass. • A mass is attached to the end of a string (simple pendulum). The mass is slightly pulled from its rest position and released. Describe the motion of the pendulum. • What do both systems have in common? HOME WORK: WkSh 19.2: Harmonic Motion Graphs

  2. What is Periodic Motion? What would happen if you slightly displace (push) the mass attached to the spring on a frictionless surface? The mass vibrates or oscillates back and forth over the same path, each cycle taking the same amount of time, the motion is called periodic.

  3. Look at the Compressed spring/Mass system again • What type of energy does the system possess when it is compressed? • spring potential energy • What type of energy does the system possess when it passes through the equilibrium position? • kinetic energy • What type of energy does the system possess when it is stretched? • spring potential energy • What is happening to the system in terms of energy? • It’s converting between spring potential and kinetic energy

  4. The Simple Pendulum • ..\..\WHSAD PHYSICS 2013 2014\pendulum-lab_en.jar

  5. Look at the simple pendulum • What type of energy does the system possess when it is at rest? • No energy • What type of energy does the system possess when it displaced from its equilibrium position? • Potential energy • What type of energy does the system possess when it is released and passes through its equilibrium position? • Kinetic energy • What is happening to the system in terms of energy? • It’s converting between potential and kinetic energy

  6. Periodic Motion: Compressed Spring/Mass • Displacement is measured from the equilibrium point • Amplitude (A) is the maximum displacement from the equilibrium point • A cycle is a full to-and-fro motion; this figure shows half a cycle • Period (T) is the time required to complete one cycle • Frequency (f)is the number of cycles completed per second

  7. Property Relations • The frequency f is inversely proportional to the period T • Unit of frequency is called the Hertz (Hz) 1Hz = 1cycle/s

  8. PHYSICS Mr. BALDWIN WAVES 15-Jan-14 AIM: How can we describe a wave? DO NOW • What are some things you know about a wave? • Light and heat energy comes to us from the Sun. How does it get here? • What is the name and call number of your favorite radio station? • Do you know what the call number represents? HOME WORK: WkSh 20.1: Waves

  9. Wave Motion: Wave characteristics • A wave is a periodic disturbance that transfers energy from one point to another • ex. light, sound, (electromagnetic {E-M} waves) • Water waves, sound waves, and light waves are very different from one another in various ways, but all have in common some basic properties: • Wavelength • Frequency • Period • Amplitude • Wave speed

  10. Wave characteristics • Amplitude, A • Frequency f and period T • Wavelength, l

  11. Wave Properties • Wavelengthl is the distance between successive points on a wave. Ex. distance between adjacent crests or troughs. • Meters (m) • The frequencyf of waves is the number of waves passing a particular point per second. • Hertz (Hz) • The periodT is the time needed for a one complete wave to pass a given point. • Seconds (s) • The amplitude A of a wave is the maximum displacement on either side of its normal position of the wave.

  12. CHECK Below is a snap shot of a wave travelling for 1 sec.About how many waves do you see?What is the period and frequency of the wave?

  13. Wave Property Relations • The frequency is inversely proportional to the period • Hz = 1/s • The wave speed is equal to the product between the frequency & wavelength • m/s • Speed of light (E-M) • c = 3.0 x 108 m/s • Range of visible light l: 380 - 720 nm.

  14. CHECK • What is a nm? • 10 -9 m • What are the call letters and numbers of your favorite radio station? • 107.5WBLS • Do you know what the numbers represent? • frequency (in MHz) • What is a MHz? • 10 6 Hz • What is the wavelength of such a wave?

  15. PHYSICS Mr. BALDWIN WAVES 23-Jan-14 AIM: How can the speed & type of a wave be determined? DO NOW • What do waves transport? • What do all waves have in common? • What is the frequency of blue light that has a wavelength of 480 nm? HOMEWORK: Worksheet: 20.1 Waves

  16. RECALL: Wave Property Relations • The frequency is inversely proportional to the period • WAVE EQUATION: The wave speed is equal to the product between the frequency & wavelength • Speed of light (E-M) • ALTERNATE FORMS

  17. Types of Waves: Transverse & Longitudinal The motion of particles in a wave can either be perpendicular to the wave direction (transverse) or parallel to it (longitudinal).

  18. Transverse Waves • Transverse waves has propagations in both the horizontal & vertical directions but perpendicular to wave direction • ex. Light (E-M) waves

  19. Longitudinal Waves • Longitudinal waves have propagation in one direction only (Unidirectional). Particles vibrate parallel to wave direction • ex. Sound waves

  20. Sound waves are longitudinal waves: pressure waves (Rarefaction)

  21. PHYSICS Mr. BALDWIN WAVES 7-Feb-14 AIM: How does sound travel? DO NOW • How is sound generated (created)? • What is an echo? • What type of wave is a sound wave? Homework: In your own words, write a short ESSAY on the Doppler Effect (do not plagiarize) & WkShts 20.1 & 21.1

  22. Standing Wave • A standing wave is generated in a pipe closed at one or both ends or on a string bounded on one or both ends. • ex. Organ pipe or guitar string • A standing wave is generated by most musical instruments. • Sound waves require the presence of matter in order to propagate. Light does not.

  23. Antinode: points that undergo maximum displacement Node: points of zero displacement What do you observe about the distance between nodes and antinodes? The distance between two consecutive nodes (or antinodes) in a standing wave is half the wavelength.

  24. Velocity of Sound • Most sound are produced by vibrating objects, such as a cone of a loud speaker. • Speed of sound depends on temperature • CHECK…What is the speed of sound at 200C? • Speed of sound at standard temperature & pressure (STP - 200C & 1atm) vsound = 343 m/s

  25. Velocity of Sound • Sound waves are described as pressure waves in a solid, liquid or gas • Sounds waves are longitudinal waves • The molecules in their path moves back and forth in the same direction as that of the wave • The velocity of sound also depends on the density of the medium. • WHY? • The denser the medium the faster it travels. • 1500 m/s in water; 5000 m/s in iron

  26. Frequency of Sound • Range of Audible Frequency of sound (sound that humans can hear): 20 Hz – 20 kHz. • Infrasonic frequency range < 20 Hz • Sources includes earthquakes, thunder, volcanoes, heavy machinery • Ultrasonic Frequency range > 20 kHz • Dogs & Bats hear in this range

  27. PHYSICS Mr. BALDWIN WAVES 5-Feb-14 AIM: How do you know a fire engine is coming towards you? (What is the Doppler Effect?) DO NOW: Describe what you observe as a siren approached you and when it goes away from you. TURN IN • Your ESSAY on the Doppler Effect • Completed Worksheets 20.1 & 21.1

  28. Velocity of Sound • How are sound waves produced? • Most sound are produced by vibrating objects, such as a vibrating cone of a loud speaker. • Speed of sound depends on temperature (0C) • CHECK…What is the speed of sound at 200C? • Speed of sound at standard temperature & pressure (STP - 200C & 1atm) vsound = 343 m/s

  29. The Doppler Effect • The apparent change in the observed frequency of a wave between a moving source and observer.

  30. It is applicable to any type of wave. • Austrian physicist Christian Doppler (1803-1853). train sound clip Simulations • physlet animation • http://www.walter-fendt.de/ph14e/dopplereff.htm

  31. Analyze this. • If the observer & source is moving apart, vs is positive • If the observer & source is moving closer, vs is negative • The velocity of sound is about 340 m/s. What are the frequencies observed as a fire engine, with siren blaring at 200Hz and moving at 17 m/s, approaches and then passes you?

  32. DO IT YOURSELF An ambulance is approaching a stationary observer. The siren of the ambulance emits a frequency of 480Hz and the speed of the ambulance is 50km/h(=13.88m/s). What wavelength and frequency will the stationary observer hear when the ambulance is approaching? Assume T=20oC.

  33. ADVANCE QUESTIONING • Determine the wavelengths of the sound waves of the siren as the fire engine approaches and as it leaves. • What are some common everyday uses of the Doppler Effect? • Doppler Radar (Weather Systems) • Red & Blue Shifts (Astronomy) • Speed detection (Police radar)

  34. A physics student sitting on the beach notices that a wave hits the beach every 5.0 seconds, and the waves seem to be about 15m apart. • What is the frequency of the waves? • What is the period of the waves? • What is the speed of these waves? • What is the frequency of laser light that has a wavelength of 623nm?

  35. PHYSICS Mr. BALDWIN WAVES AIM: What are the properties of sound? DO NOW • Describe a longitudinal wave. • Describe a transverse wave. Homework: Handout

  36. PHYSICS Mr. BALDWINWAVES 11-Feb-14 AIM: What happens when you exceed the speed of sound? How loud is loud? DO NOW: QUIZ: Handout Homework: Handout

  37. The graph below displays how displacement varies with TIME when a wave passes a fixed point at a speed of 12.0 m/s. How many waves are there? What is the amplitude of the wave? Determine the frequency and wavelength of the wave based on the previous information.

  38. LOUDNESS • Noise is measured in units called decibels (dB), on a scale from zero to 140. The higher the number in decibels, the louder the noise. • For every 20 dB increase, a sound is twice as loud.

  39. OBSERVE • What do you observe about the wave-fronts as the source approaches the speed of sound? • http://dev.physicslab. • org/asp/applets/doppler/default.asp

  40. The speed of sound • What is the speed of sound at STP? • The speed of sound in air is 343 meters per second at one atmosphere of pressure and room temperature (20°C). • Convert this to mph (1mi=1609m) • (760 miles per hour) • An object is subsonic when it is moving slower than sound. • An object is transonic when it is moving at the speed of sound.

  41. We use the term supersonic to describe motion at speeds faster than the speed of sound. • A shock waveforms where the wave fronts pile up. • The pressure change across the shock wave is what causes a very loud sound known as a sonic boom.

  42. Mach number The unitless Mach number was named after the Austrian physicist Ernst Mach. The Mach number is ratio of the speed of the aircraft to the speed of sound . An airplane flying at less than Mach 1 is traveling at subsonic speeds; at about Mach 1, or transonic , it is at the speed of sound, and greater than Mach 1 is supersonic . An aircraft traveling at Mach 2 is traveling at twice the

  43. Mach vs. Knot • http://www.grc.nasa.gov/WWW/k-12/BGA/Corrine/mach_number_wks.htm • http://www.grc.nasa.gov/WWW/K-12/WindTunnel/Activities/knots_vs_mph.html

  44. PHYSICS Mr. BALDWINWAVES 12-Feb-14 AIM: What is light? What is the electromagnetic (E-M) spectrum? DO NOW: What are the colors of the rainbow? Why are they different? How is it that heat comes to us from the Sun? Homework: Worksheet 24.1 - The Electromagnetic Spectrum

  45. Electromagnetic Waves • The electromagnetic spectrum consists of all types of electromagnetic radiation • Gamma rays, x-rays, ultraviolet radiation, visible light, infrared radiation, millimeter waves, microwaves, and radio waves are all electromagnetic waves that differ only in their frequencies & wavelengths. • ALL Electromagnetic waves travel in a vacuum with the same speed of light. (300,000,000 m/s) • Write this in scientific notation.

  46. Infrared radiation (IR) created by molecular vibrations Visible light (white light) created by electron excitation Ultraviolet radiation (UV) created by electron excitation X-ray radiation created by high energy electron excitation Gamma (γ) radiation created within the atomic nuclei by high energy nuclear processes Ionization Radiation is any radiation that is energetic enough to ionize biological matter. Causes genetic mutation of DNA Penetrate deep into matter As λ decreases, the f increases, and hence the energy E increases Electromagnetic Spectrum

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