Chapters 14 to 19

1. Chapters 14 to 19

2. Waves There are two kinds of motion: • Harmonic motion- Movement that repeats over and over again. • Linear motion- Moving from one place to another (We have learned much about this) Waves are a type of harmonic motion

3. Harmonic vs. Linear So far we have talked about objects moving from one place to another. This is called linear motion. Distance, time, speed and acceleration all come from linear motion. • Ex: A bicycle moves with linear motion, but the pedals rotate with harmonic motion.

4. Terms to describe waves: • Cycle: The motion from beginning to end before it begins repeating. • Period (T): The time it takes to complete one cycle. Metric SI Unit: (s) seconds • Frequency (f): The number of cycles that occurs in a second. Metric SI Unit: (Hz) Hertz or (s-1) inverse seconds • Amplitude: How big the wave is or how far away from its origin it is. Unit depends on the kind of wave.

5. Parts of a wave Wavelength (): The distance between two crests or two trough s Crest: The highest point of the wave Amplitude: How far the wave is from the origin Trough: the lowest point of the wave

6. Sound vs. Light • Light waves move up and down and we call them Transverse waves. That means the wave moves perpendicular to the direction it is traveling.

7. Sound Waves move back and forth. They are called Longitudinal. That means the wave moves parallel to the direction it is traveling.

8. Sometimes waves are named by how they are created. • Light is made from Electromagnetic radiation and is called an Electromagnetic wave. • Sound is made from matter squeezing together or stretching apart and is called a Compressional wave.

9. Both waves have the same parts; they just look a little different. Crest Trough Trough Compression: Where the density is the largest Rarefaction: Where the wave density is smallest Different names are given to the corresponding parts

10. Because a compression wave depends on the different density of something, it needs a medium. A medium is the stuff that the compressional wave travels in. If you screamed on the moon, would you be heard? Electromagnetic radiation (light) does not need a medium to travel. Thankfully, otherwise the earth would be pretty dark.

11. Doppler Effect • Doppler effect happens as objects making sound move past a stationary observer. • The police car siren sounds higher pitched as it is approaching and lower pitched when it is driving away. • Remember: a shorter wavelength will give a higher frequency and a higher frequency of sound has a higher pitch.

12. The waves of sound are squeezed as they approach and stretched as they leave.

13. How are waves analyzed? Some waves can travel at different speeds. The velocity of the wave can be calculated using the following formula: Light travels at a constant speed in a vacuum and its velocity is given the symbol (c). The speed of light is c = 2.99x 108 m/s

14. Waves carry Energy • The higher the frequency the higher the energy. f = E • The longer the wavelength the lower the energy.   = E

15. Waves can move a variety of ways Reflection: The wave can bounce off and go in a new direction. Refraction: The wave slows down when it passes through a medium that is more dense and it bends

16. Diffraction: How light and sound can bend around corners and as they pass through holes Absorption: The wave can be absorbed by a material and disappear.

17. Waves can also interact with each other We call this interference and there are two kinds of interference: This happens when the crest of one wave overlaps with the crest of another wave. The new wave becomes bigger or has more amplitude.

18. Destructive interference is when the crest of one wave overlaps the trough of another wave and the new wave is smaller or has less amplitude.

19. What would interference between these pairs of waves look like? Is it constructive or destructive interference?