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Waves

Learn about the fundamentals of waves in physics, including types of waves, their properties, and how they are measured. Explore topics such as transverse and longitudinal waves, standing waves, nodes and anti-nodes, and measuring earthquakes using seismographs.

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Waves

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  1. Waves Pre-AP Physics Ness

  2. Start with the basics.. • Everything around us wiggles and jiggles, even things we can’t see such as ATOMS vibrates. • Vibrations can’t exist in one instant, it has to move back and forth.

  3. Waves • A wave is a disturbance that transfers energy through matter or space or in simple terms…

  4. Notice the particle is in the same spot…

  5. Waves through a medium • A medium is any substance that a wave can move through. • Example: • Water • Air • Slinky • Jump rope

  6. NO Medium vs Medium

  7. Two properties of medium effect the speed of a wave: • Density: waves move slower in a more dense medium. • Elasticity: (think of a rubber band):it returns back to its original shape. Waves move faster if it’s in a more elastic medium. Soooooo – a medium effects the speed of a wave!!!

  8. Parts of a transverse wave:

  9. One more Part of a transverse wave: Amplitude – indicated the energy of the wave – or the height of the wave from origin to crest or from origin to trough.

  10. One more Part of a transverse wave: Wavelength – distance in meters We use the symbol = λ

  11. One more Part of a transverse wave: Frequency – is the number of complete waves at a given point (cycle) per time. * We use the unit Hertz or Hz.

  12. Transverse Waves • Transverse waves – the one that we are most familiar with!

  13. Parts of a longitudinal wave

  14. Longitudinal Wave • There are two part of this wave: • Compression- in which the molecules are crowded together. • Rarefaction – molecules are spread out.

  15. Ocean Waves • It is a combination of transverse and longitudinal waves.

  16. Standing waves • Are waves that are trapped between boundaries. • To keep a standing wave going it needs to have a driven end: and end that gives energy to the wave.

  17. Nodes and Anti-nodes • The places of no amplitude are called NODES. • The places of greatest amplitude are called ANTI-NODES

  18. Harmonics • Harmonics have nodes at the boundaries. Harmonics sound louder, keep their energy longer, and take less energy to produce.

  19. Let’s calculate the speed of a wave: • Speed = wavelength X frequency • If you have a wave that has a frequency of 4 Hz and wavelength of 2 meters. What is the speed of the speed? Steps: 1. Write out the variables 2. Manipulate the equation if needed… 3. Substitute given numbers in the problem 4. Solve for the unknown ( calculate)

  20. Now it’s your turn: • What is the frequency of a wave that has a wavelength of 5 meters and a speed of 250 m/sec?

  21. Another one… • A wave on a certain guitar string travels at a speed of 200m/s. Calculate the wavelength of an “A” note sounding at 440Hz.

  22. Earthquakes Have you ever experienced one? https://video.nationalgeographic.com/video/101-videos/00000144-0a2d-d3cb-a96c-7b2d6cd80000?source=relatedvideo

  23. Earthquakes can be caused by:1. Eruptionof avolcano

  24. Earthquakes can be caused by:2. Collapse of a cavern

  25. Earthquakes can be caused by:3. Impact of a meteorite

  26. Earthquakes can be caused by:4. Strain built up along boundaries between plates

  27. A fault is… • A break in the lithosphere along which movement has occurred. • Most earthquakes occur in this way. • Friction between plates prevents them from moving, so strain builds up. Eventually, the strain becomes great enough that the rock moves, and returns to normal shape. This causes an earthquake (elastic rebound theory).

  28. Focus: the point at which the rock first breaks and moves in an earthquake. Below the surface. • Epicenter: the point on the earth’s surface directly above the focus.

  29. Seismic Waves • The energy released in an earthquake travels in waves. There are three types: • Primary waves (P waves) • Secondary waves (S waves) • Surface waves (Love and Rayleigh)

  30. Primary Waves • Called P waves • Compression waves-squeeze and stretch rock(Push and Pull) • Can travel through any material-solid, liquids, and gases • Travel the fastest

  31. Secondary Waves • S waves • Side to Side movement. • Can travel only through solid material, not liquids or gases • Travel a little more than half the speed of P waves

  32. Surface Waves • Seismic waves that travel along Earth’s Surface • When P and S waves reach the surface, they make Surface waves • There are two types, Love waves and Rayleigh waves • Cause lots of damage

  33. Measuring Earthquakes • Seismograph: Instrument used tomeasure an Earthquake • Seismogram: The paper record of the Earthquake data (shaking) is called a seismogram

  34. The S-P Time Interval is thetime between the start of the p wave and the s wave.

  35. Locating Earthquakes • Because P waves and S waves travel at different speeds, the difference in their arrival times can be used to determine the DISTANCE away an earthquake occurred.

  36. Locating Earthquakes • If you know the distance an earthquake occurred from at least three different seismic stations, you can determine the location of the epicenter. • Triangulation: Using the S-P time interval data from 3 stations to determine the epicenter

  37. Earthquake Magnitude: strength measured by the amount of released energy • Richter Scale by Charles Richter • Each increase in number represents 10x an increase in power. • Example: a 4.0 is ten times stronger than a 3.0

  38. Earthquake Hazards • Fire: Causes the most damage in an Earthquake, some utility lines and roads get damaged • Liquefaction: When the ground turns to quicksand due to the shaking • Tsunamis: Are caused by underwater earthquakes that make a big wave.

  39. Boundary Behavior • The behavior of a wave when it reaches the end of its medium is called the wave’s BOUNDARY BEHAVIOR. • When one medium ends and another begins, that is called a boundary.

  40. Fixed End • Here the incident pulse is an upward pulse. • The reflected pulse is upside-down. It is inverted. • The reflected pulse has the same speed, wavelength, and amplitude as the incident pulse.

  41. Fixed End Animation

  42. Change in Medium • Another condition is when the medium of a wave changes. • Think of a thin rope attached to a thick rope. The point where the two ropes are attached is the boundary. • At this point, a wave pulse will transfer from one medium to another. • What will happen here?

  43. Change in Medium • In this situation part of the wave is reflected, and part of the wave is transmitted. • Part of the wave energy is transferred to the more dense medium, and part is reflected. • The transmitted pulse is upright, while the reflected pulse is inverted.

  44. Change in Medium • The speed and wavelength of the reflected wave remain the same, but the amplitude decreases. • The speed, wavelength, and amplitude of the transmitted pulse are all smaller than in the incident pulse.

  45. Change in Medium Animation Test your understanding

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