2. Waves

3. Waves Disturbance that carries energy through matter or space The matter through which a wave travels is called a medium Waves spread out in circles (wave front) that get bigger as the waves move farther from the center Wave front energy most concentrated energy most spread out

4. Energy in the form of Waves Essentially energy is being transferred through waves Two main types of waves: 1. Electromagnetic – “no stuff needed”-Particles – Ex: Light 2. Mechanical – “stuff needed”-Particles – Ex: Sound

5. Room Example Pretend we take all of the air out of this room... Besides exploding, what would happen if we tried to conduct class?

6. The speed of waves depends on the medium through which they travel. Sound waves travel faster in solids than in gas or in liquid. Light waves travel slower when they have to pass through solids, gases or liquids. Waves that require a medium are called mechanical waves. Most waves are mechanical with the exception of light waves – which make up the electromagnetic spectrum. http://aspire.cosmic-ray.org//labs/seismic/ Wave Movement

7. Types of Waves 1.Transverse motion of particles is perpendicular to motion of wave Ex. Rope 2. Longitudinal motion of particles is parallel to motion of wave Ex. Slinky US http://aspire.cosmic-ray.org//labs/seismic/

8. Types of Waves 3. Surface motion of particles move both parallel & perpendicular producing a circular motion Ex. Water waves Wave Characteristics 1. Crest highest point 2. Trough lowest point 3. Amplitude half the distance between crest & trough 4. Wavelength (lambda) – distance from one crest/trough to next crest/trough; measured in meters (m) 5. Frequency (f) - # of wavelengths that pass a point in a given time interval; measured in Hertz (Hz) http://aspire.cosmic-ray.org//labs/seismic/long_waves.swf

10. Period vs. Frequency Period – # of seconds it takes for one wave to pass Frequency – # of waves that pass by in one second

11. Sound Waves Properties of Sound Waves: Are longitudinal waves, like that of a stretched spring Caused by vibrations Spread in all directions from the source Like the coils in a slinky, some areas are compressed, while others are stretched Compressions Rarefactions These areas are called Compressions and Rarefactions

13. Speed of Sound Depends on the material of the vibrating medium Sound can vibrate water, wood (speaker enclosures, pianos), metal, plastic, etc. Sound speed in dry air is 330 meters/second at 0 o C Faster in warm air, slower in cold Water 4 times faster, steel 15 times faster EVERYONE STAND UP AND LINE THE BACK OF THE ROOM

14. Sound Waves

15. Relative intensity of sound is measured in decibels, dB Loudness is perceived on a logarithmic scale

17. Molecules in the air vibrate about some average position creating the compressions and rarefactions. We call the frequency of sound the pitch.

19. Sound Waves Pitchfrequency Pitch is determined by frequency : High-pitched sounds have high frequencies Low-pitched sounds have low frequencies Infrasound Infrasound -Sound waves with frequencies lower than 20 Hz Ultrasound Ultrasound -Sound waves with frequencies higher than 20,000 Hz

20. Go to EMS, Wave Basics 2 and Wave Behaviors

21. Sound Waves Resonance occurs when vibrations of one object cause the vibration of another object at a natural frequency Tacoma Narrows Bridge Disaster aka “Galloping Gertie” Tacoma Narrow Bridge Disaster Video

22. Sound Waves How do humans hear? Our eardrums act somewhat like normal drums, only in a reversed fashion How do bats hear? Bats use ultrasonic sonar location Bats use reflected sound waves to determine the distance to, and location of, objects

23. Sound Waves Ultrasound is also used in medicine This method is known as Ultrasonography and we see a picture known as a Sonogram

24. Doppler Effect an observed change in the frequency of a wave when the source or observer is moving http://www.explorelear ning.com/index.cfm?m ethod=cResource.dspV iew&ResourceID=19

26. Wave Speed Wave speed is equal to the frequency multiplied by the wavelength; v = f (lambda) Sample Problems: 1.The average wavelength of ocean waves is 15.0 m and the frequency is 0.10 Hz. What is the average speed of the waves? 2.A wave along a guitar string has a frequency of 440 Hz and travels at a speed of 660 m/s. What is the wavelength? 3.The speed of sound in air is about 340 m/s. What is the frequency of a sound wave that Has a wavelength of 1.50 m? significant figures practice site

27. Electromagnetic Spectrum

28. Wave Interactions Occur when waves meet objects or other waves in a medium Reflection the bouncing back of a wave as it meets a surface or boundary Ex. Light waves striking a shiny surface Reflection at a Free Boundary the reflected wave is exactly like the original wave Ex. A US

29. Wave Interactions Reflection at a Fixed Boundary the reflected wave is like the original wave, but is turned upside down and travels in the opposite direction follows Newton’s Third Law…Equal but opposite force is exerted Ex. B

30. Diffraction the bending of a wave as it passes an edge or an opening Ex. Hearing people speak when standing outside the doorway of a room (picture B/A) Picture A/B demonstrates waves bending and spreading out into the space behind the block Picture B/A demonstrates waves bending around two edges and spreading out as they pass through the opening

31. Refraction the bending of waves as they pass from one medium to another Ex. a spoon in a glass of water the top of the spoon handle has light waves passing directly from the spoon through the air to your eyes the rest of the spoon has light waves passing through the water, then the glass, and finally to your eyes (each time bending slightly)

32. Interference the combination of two or more waves that exist in the same place at the same time these waves combine to produce a single, new wave that is different than the original Ex. water waves passing through each other

33. Constructive Interference Destructive Interference any interference in which waves combine so that the resulting wave is bigger than the original waves any interference in which waves combine so that the resulting wave is smaller than the largest of the original waves

34. Interference of Light waves may produce colorful displays Ex. soap bubbles two sets of light waves reach our eyes 1. those that bounce off the outside of the bubble 2. those that bounce off the inside of the bubble

35. Interference of Sound Waves  produce beats if sound wave frequencies are different, their compressions arrive at your ear at different rates

36. Standing Waves nodes antinodes a wave form caused by interference that appears not to move along the medium and that shows some regions of no vibration (nodes) and other regions of maximum vibration (antinodes) cause the medium to vibrate in a loop or in a series of loops Nodes – lie @ points where the crests of the original waves meet the troughs of the reflected waves Antinodes – form where the crests of the original waves line up with the troughs of the reflected waves

37. Standing Waves (continued) can only have certain wavelengths can exist whenever a multiple of half-wavelengths will fit exactly in the length of the string Musical instruments rely on standing waves

38. The End