Ch 20 The Energy of Waves

1. Ch 20 The Energy of Waves The Nature of Waves

2. The Nature of Waves • Wave- Any disturbance that transmits energy through matter or empty space. • Wave Energy • Energy can be carried away from its source by a wave • Waves transfer energy – NOT MATTER. • https://www.bing.com/videos/search?q=wave+pool+video&src=IE-TopResult&conversationid=&ru=%2fsearch%3fq%3dwave%2bpool%2bvideo%26src%3dIE- • TopResult%26FORM%3dIETR02%26conversationid%3d&view=detail&mmscn=vwrc&mid=153AFD72B76A0E026E95153AFD72B76A0E026E95&FORM=WRVORC • What causes a wave in the first place???? When a source of energy causes a vibration to move through a medium

3. Energy Transfer Through a Medium Medium- a substance through which a wave can travel. Can be a solid, liquid, or gas. When a particle vibrates (moves back and forth) it can pass its energy to a particle next to it. Some waves don’t need a medium

4. Types of Waves • Transverse Waves- Waves in which the particles vibrate in an up-and-down motion. • Particles move across, or perpendicular to the direction the wave is going. • Crest- The highest point of a transverse wave. • Trough- The lowest point of a transverse wave (between 2 crests) • https://www.youtube.com/watch?v=7cDAYFTXq3E ( transverse vs. longitundal)

5. Types of Waves • Longitudinal Waves- The particles of the medium vibrate back and forth along the path the wave moves. Particles move parallel to the direction the wave is moving • Compression- A part of a longitudinal wave where the particles are crowded together. • Rarefaction-A part where the particles are spread apart. • Sound waves are longitudinal waves.

6. 1.2 Properties of Waves • Amplitude – Height of a wave. • The larger the amplitude is, the taller the wave is. • The larger the amplitude is, the more energy the wave has • From the middle to either the crest or the trough

7. Properties of Waves • Wavelength- distance between a point on one wave and the same point on the next wave • For longitudinal waves, it is the distance between compressions • For transverse waves, it is the distance from crest to crest • The shorter the wavelength the more energy the wave has.

8. Properties of Waves • Frequency- The number of waves produced in a given amount of time. • Expressed in Hertz (Hz) • 1 Hz = 1 wave 1 second • Higher frequency means higher energy • In one second, how many waves??? • TopResult%26FORM%3dIETR02%26conversationid%3d&view=detail&mmscn=vwrc&mid=153AFD72B76A0E026E95153AFD72B76A0E026E95&FORM=WRVORC • (when???) • TopResult%26FORM%3dIETR02%26conversationid%3d&view=detail&mmscn=vwrc&mid=153AFD72B76A0E026E95153AFD72B76A0E026E95&FORM=WRVORC • (how old are you?)

9. The period of a wave is the time for a particle on a medium to make one complete cycle. SI Unit = Seconds (s) Frequency and period are related Frequency refers to how often something happens . Period refers to the time it takes something to happen Equation: p = 1/f What is the period of a wave that has a frequency of 4 Hz? What is the frequency of a wave that has a period of 3 seconds?

10. Properties of Waves • Wave Speed: • The speed at which the wave travels • V = λ x f • SI Units Speed: m/s Wavelength: m Frequency: Hz • For a wave to move really fast it needs to have a short wavelength and a high frequency As the frequency increases, and the wavelength decreases As the wavelength increases, the frequency decreases Frequency and wavelength are inversely related because as one goes up, the other goes down. https://www.bing.com/videos/search?q=video+on+types+of+waves&&view=detail&mid=F15AB91E2E971459FC53F15AB91E2E971459FC53&&FORM=VRDGAR(properties) https://www.bing.com/videos/search?q=wave+physical+science+video&&view=detail&mid=D8A6859B449052E6B6BDD8A6859B449052E6B6BD&&FORM=VRDGAR (intro)

11. Calculations • Determine the wave speed of a wave that has a wavelength of 5 m and a frequency of 4 Hz. • What is the frequency of a wave if the wave has a speed of 12 m/s and a wavelength of 3 m? • A wave has a frequency of 5 Hz and a speed of 18 m/s. What is the wavelength?

12. How is wavelength related to frequency if the wave is traveling at a constant speed? • How is energy related to the amplitude of a wave? • Describe two ways to measure the wavelength of wave. • If you double the frequency of a wave, what will happen to its wavelength if the speed does not change?

13. Wave Interactions • Transmitted Waves • Refraction- The bending of a wave as the wave passes from one medium to another at an angle • Wave speed changes when a wave moves from one medium

14. Refraction of Different Colors • Dispersion- Light rays are spread out into separate colors. • Each color of light has it’s own wavelength. • Diffraction- The bending of waves around a barrier or through an opening that changes its direction

15. Wave Interactions • Interference- Waves occupy the same space at the same time. • Constructive Interference- the crest of one wave overlaps the crest of another wave. • The new amplitude of the combined wave is larger than the original waves • Bridge collapse • https://www.bing.com/videos/search?q=video+bridge+collapse+constructive+interference+what+caused&&view=detail&mid=1EEED8ADB11F8FE7FB931EEED8ADB11F8FE7FB93&&FORM=VRDGAR

16. Destructive interference- two or more waves combine to produce a wave with a smaller displacement The crest of one wave overlaps with the trough of another wave. The new amplitude of the combined wave is smaller than the original waves. Ex. Noise canceling head phones https://www.bing.com/videos/search?q=deconstructive+interference%ee%80%81+noise+%ee%80%80cancelling+headphones+video&docid=608040966236210999&mid=A0CE94719118C48FC269A0CE94719118C48FC269&view=detail&FORM=VIREHT

17. Constructive & Destructive Interference