WAVES – Chpt. 14

1. WAVES – Chpt. 14

2. What in the World Will I Learn? • You will determine how waves transfer energy. • You will learn the parts of a wave. • You will describe wave reflection and discuss its practical significance.

3. The Big Bad Truth First! • Scientists have a theory about waves and particles. • What ever could this be called? • Why does Mrs. Warren think this is important for me to know?

4. Wave – Particle Duality Let’s use an analogy from Leonard!

5. Waves

6. WAVES a disturbance that transfers energy • Carries energy from one place to another • Classified by what they move through • Mechanical Wavesthe energy is transferred by vibrations of medium (medium = matter)ex/ ocean waves move through water • Electromagnetic waves (EM Waves)the energy moves through disturbances in the electromagnetic field.

7. Making a pulse MECHANICAL WAVES require a medium (the material through which the disturbance is moving) to transmit energy travel through & gradually lose energy to that medium • Examples: • water, sound, rope, & spring waves • Mechanical Media: • water, air, rope, spring

8. Slinkin’ into Waves • Working in your groups answer the following questions: • 1. What do you think the difference is between a wave pulse and the wave’s vibration? • Place the slinky on the floor. One person should hold one end of the slinky still, while the other person begin moving the slinky up and down. • 2. What happens when you move the slinky up and down? What happens when you increase your speed? Which direction is the wave pulse? Which direction is the vibration? • Again, place the slinky on the floor. One person should hold one end still, and the other person should move the slinky in a horizontal direction (it’s like giving the slinky a push). • 3. Look very closely to the slinky. Do you see anything while watching the slinky? Describe what you see. Which direction is the wave pulse? Which direction is the vibration? • 4. What’s the difference between the 2 types of waves you experimented with?

9. Longitudinal, transverse, surface MECHANICAL WAVES Classified by how medium vibrates Pulse = direction of energy transfer; more specifically, a single bump or disturbance in a medium. Vibration = direction of vibration of medium relative to pulse 3 types:

10. MECHANICAL WAVES Classified by how medium vibrates Longitudinal Waves: Vibration is in the same direction as wave pulse (parallel to wave pulse) Transverse Waves: Vibration is at 900 (right angles)to wave pulse Surface Waves: Vibration is circular Ex/ Ocean waves

11. MECHANICAL WAVES • Small Video discussing the differences between types of waves.

12. Surface Waves

13. TRANVERSE WAVES Vibration is perpendicular to the direction of the motion of the wave

14. Rarefraction (expansion) Compression LONGITUDINAL WAVES Vibration is parallel to the direction of the motion of the wave • Also called compression or pressure wave • Examples: • P-type earthquake waves • Sound waves

15. Connecting Physics and Earth • P Wave Earthquake Waves # 1 • P Wave Example #2 • S wave Earthquake #1 • S Wave Example #2

16. Waves describe the Earth P waves move through solids & liquids P waves move through solids & liquids S waves move through solids only!!! Are these MECHANICAL WAVES???? YES!! Seismic waves need a medium (the earth!)

17. WAVE STRUCTURE CREST (peak) AMPLITUDEresting to max peak WAVELENGTH TROUGH

18. AMPLITUDE • Measures DISPLACEMENT • Distance between “rest & crest” or “rest & trough” • Gives indication of “power” or “strength” of wave(magnitude of earthquake = Richter scale) • Does not affect velocity of wave • Determines loudness (sound) or brightness (EM wave)

19. WAVELENGTH  • Distance between any two repeating points on a wave (also called a cycle)crest-crest, trough-trough,expansion-expansion, compression-compression • Determines what colorswe see; what notes we hear (pitch) • Shorter wavelengths have more cycles per minute because they aren’t as long

20. VELOCITY v • the rate at which the energy travels; speed & direction because it’s a …. • Depends on medium • Mechanical waves travel faster through dense mediums • EM Waves are faster through less dense mediums

21. Frequency ƒ • How oftennumber of wavelengths that pass any point in 1 second. • measured in wavelengths/second or cycles/secondHertz (Hz) = number of wavelengths in 1 second • Frequency is related to velocity and wavelength: • v = ƒ 

22. PERIOD T • How longAmount of time for one wavelength to pass a point • Related inversely to frequency Period= 1 Frequency 1=1T f

23. Example Time!  • A sound wave has a frequency of 262 Hz and a wavelength measured at 1.29 m. • Part a) What is the speed of the wave? • Part b) How long will it take the wave to travel the length of a football field, 91.4 m? • Part c) What is the frequency of the wave? Let’s break it down ya’ll!

24. Example Part a • A) What is the speed of the water? frequency = 262 Hz, wavelength = 1.29 m v = ƒ  Which variable are we solving for? Let’s plug it in!!

25. Example Part b • How long will it take the wave to travel the length of a football field, 91.4 m?

26. Example Part c • Find the frequency from the period. • We knew period, we know the equation, we need to find frequency.