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Table of Contents

Learn about the basics of waves, including their properties, interactions, and the nature of seismic waves. Explore transverse and longitudinal waves, wave measurements, and calculations.

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Table of Contents

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  1. Table of Contents • What Are Waves? • Properties of Waves • Interactions of Waves • Seismic Waves

  2. What are Waves? • Remember back…… • A wave is a disturbance that transmits energy through matter or space.

  3. One Way to Classify Waves • Mechanical Waves • Must have a medium • Can travel at any speed • Ex: • Electromagnetic Waves • Do NOT need a medium • Travel at the speed of light • Ex:

  4. - What Are Waves? Mechanical Waves and Energy • Waves travel through water, but they do not carry the water (or the duck) with them.

  5. Mechanical Waves • Examples Include: • Ocean waves, medium = water • Sound waves, medium = air • Seismic Waves (Earthquake), medium = earth

  6. Wave Movement • A wave front is the front of a wave that is transferring energy. • In a single system all of the wave fronts have the same amount of energy, but as the wave front spreads out, so does the energy.

  7. - What Are Waves? Transverse Waves • Waves that move the medium at right angles (perpendicular) to the direction in which the waves travel are called transverse waves.

  8. - What Are Waves? Longitudinal Waves • Longitudinal waves move the medium parallel to the direction in which the waves travel.

  9. - What Are Waves? Longitudinal Waves • The compressions of a longitudinal wave correspond to the crest of a transverse wave. The troughs correspond to rarefactions.

  10. - What Are Waves? Transverse vs. Longitudinal Waves • Click on the link to see how the differ waves travel or propogate. • Another link with animation

  11. - Properties of Waves Wave Properties • The basic properties of all waves are amplitude, wavelength, frequency and speed.

  12. Parts of a Wave • Wavelength (λ) is the total length of 1 wave. • In transverse waves it’s typically measured from crest to crest or trough to trough. • In longitudinal waves it’s measured from compression to compression or rarefaction to rarefaction. • The shorter the wavelength, the more energy the wave is carrying. 1 λ 1 λ 1 λ 1 λ

  13. Parts of a Wave • Amplitude can be measured on a transverse wave. It height from the resting point to the crest or the resting point to the trough. • The larger the amplitude, the more energy the wave is carrying. Amplitude Amplitude

  14. Wave Measurements • The frequency (f)of a wave is the number of complete waves that pass a given point per second. • The SI unit for measuring frequency is Hertz (Hz). • 1 waves occurs every second= 1 Hz • 2 waves occur every second= 2 Hz

  15. Wave Measurements • Frequency and wavelength have an INVERSE relationship--as one increases, the other decreases. • Example: The higher the frequency the shorter the wavelength and vice versa.

  16. Wave Measurements • Wave speed (v) is the speed at which a wave passes through a medium and is measured using the following equation: • wave speed (m/s) = frequency (Hz) x wavelength (m) • v = f x λ

  17. The speed of a wave on a rope is 50 cm/s and its wavelength is10 cm. What is the wave’s frequency? Read and Understand What information have you been given? Speed = 50 cm/s Wavelength = 10 cm - Properties of Waves Calculations

  18. The speed of a wave on a rope is 50 cm/s and its wavelength is10 cm. What is the wave’s frequency? Plan and Solve What quantity are you trying to calculate? The frequency of a wave = __ Hz What formula contains the given quantities and the unknown quantity? Frequency = Speed/Wavelength Perform the calculation. Frequency = Speed/Wavelength= 50 cm/s/10 cm Frequency = 5/s= 5 Hz - Properties of Waves Calculations

  19. The speed of a wave on a rope is 50 cm/s and its wavelength is10 cm. What is the wave’s frequency? Look Back and Check Does your answer make sense? The wave speed is 50 cm per second. Because the distance from crest to crest is 10 cm, five crests will pass a point every second. - Properties of Waves Calculations

  20. Practice Problem A wave has a wavelength of 2 mm and a frequency of 3 Hz. At what speed does the wave travel? (2 mm)(3 Hz) = 6 mm/s - Properties of Waves Calculating Frequency

  21. Practice Problem The speed of a wave on a guitar string is 142 m/s and the frequency is 110 Hz. What is the wavelength of the wave? (142 m/s)/(110 Hz) = 1.3 m - Properties of Waves Calculating Frequency

  22. STOP HERE Lets do the Wave!

  23. Wave Measurements • A wave along a guitar string has a frequency of 440 Hz and a wavelength of 1.5 m. What is the speed of the wave? v = ? m/s f = 440 Hz λ = 1.5 m v = f * λ v = 440 Hz x 1.5 m v v = 660 m/s f * λ

  24. Wave Measurements • The speed of sound in air is about 340 m/s. What is the wavelength of sound waves produced by guitar strings vibrating at a frequency of 440 Hz? v = 340 m/s f = 440 Hz λ = ? m λ = v / f λ= 340 m/s / 440 Hz v λ= 0.77 m f * λ

  25. Wave Measurements • The speed of light is 3 x 108 m/s. What is the frequency of microwaves with a wavelength of 0.01 m? v = 3 x 108 m/s 300,000,000 m/s f = ? Hz λ = 0.01 m f = v / λ f = 300,000,000 m/s / 0.01 m v f = 30,000,000,000 Hz f * λ

  26. End of Section:Properties of Waves

  27. - Interactions of Waves Reflection • When an object or wave hits a surface through which it cannot pass, it bounces back.

  28. Reflection • Reflection is when waves, whether physical or electromagnetic, bounce from a surface back toward the source. A mirror reflects the image of the observer. NORMAL

  29. - Interactions of Waves Refraction • When a wave enters a new medium at an angle, one side of the wave changes speed before the other side, causing the wave to bend.

  30. Refraction • Refraction is when waves, whether physical or electromagnetic, are deflected when the waves go through a substance. The wave generally changes the angle of its general direction.

  31. Refraction

  32. - Interactions of Waves Diffraction • When a wave moves around a barrier or through an opening in a barrier, it bends and spreads out.

  33. Diffraction • Diffraction is when a wave goes through a small hole and has a flared out geometric shadow of the slit. • a characteristic of waves of all types • We can hear around a corner because of the diffraction of sound waves. For instance, if a wall is next to you when you yell, the sound will parallel the wall. The wall may stop, but the voice doesn't; sound will almost turn the corner of the wall.

  34. http://www.acoustics.salford.ac.uk/schools/teacher/lesson3/flash/whiteboardcomplete.swfhttp://www.acoustics.salford.ac.uk/schools/teacher/lesson3/flash/whiteboardcomplete.swf

  35. Wave Behavior • Interference occurs when the combination of two or more waves exist in the same place at the same time. • Constructive interference = bigger wave. • Destructive interference = smaller wave.

  36. The interference that occurs when waves combine to make a wave with a smaller amplitude is called destructive interference. - Interactions of Waves Interference • The interference that occurs when waves combine to make a wave with a larger amplitude is called constructive interference. Link to animation of interference and standing waves. Another cool animation!

  37. - Interactions of Waves Wave Interference Activity • Click the Active Art button to open a browser window and access Active Art about wave interference.

  38. - Interactions of Waves Standing Waves • If the incoming wave and a reflected wave have just the right frequency, they produce a combined wave that appears to be standing still. • ex: Jump rope Link to standing wave animation- watch for >1 min

  39. Standing Waves • Nodes: Point of zero amplitude • Nodes are always spaced evenly throughout the standing wave. • Antinodes: point of maximum amplitude (MAX energy)

  40. Resonance • Most objects have a natural frequency of vibration • If a nearby object vibrates at the same frequency this can cause resonance. • Examples: instruments • Show water glass demonstration

  41. Doppler Effect • https://www.youtube.com/watch?v=h4OnBYrbCjY

  42. - Interactions of Waves Asking Questions • Before you read, preview the red headings. In a graphic organizer like the one below, ask a what, how, when, or where question for each heading. As you read, write answers to your questions. Question Answer Waves are reflected when they hit a surface through which they cannot pass and bounce back. How are waves reflected? The bending of waves due to a change in speed What is refraction? When a wave moves around a barrier or through an opening in a barrier When does diffraction occur? A wave that appears to stand in one place even though it is really two waves interfering What is a standing wave?

  43. End of Section:Interactions of Waves

  44. Graphic Organizer Waves can be can be Transverse Longitudinal contain contain contain contain Crests Troughs Compressions Rarefactions

  45. End of Section:Graphic Organizer

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