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Chapter 15 Characteristics of Waves

Chapter 15 Characteristics of Waves. 15.1 What are Waves?. Wave : a disturbance that transfers energy from place to place Waves can travel through material called a medium ; can be gas, liquid, or solid. Mechanical waves require a medium through which to travel

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Chapter 15 Characteristics of Waves

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  1. Chapter 15Characteristics of Waves

  2. 15.1 What are Waves? • Wave: a disturbance that transfers energy from place to place • Waves can travel through material called a medium; can be gas, liquid, or solid. • Mechanical waves require a medium through which to travel • Energy passes from particle to particle, like food passed around a table • Energy is transferred but medium does not move, food is transferred but people do not move • Electromagnetic waves do NOT require a medium through which to travel

  3. 15.1 What are Waves? • An energy source causing a medium to vibrate produces mechanical waves • Vibration: repeated motion • Mechanical waves are classified by movement

  4. Types of Waves • Transverse Waves • Particles move at right angle to direction of the wave • Crest: highest part of wave • Trough: lowest part of wave • Longitudinal Waves • Particles move parallel to direction of the wave • Compression: particles are pushed together • Rarefaction: particles are spread out

  5. Representing Types of Waves • Longitudinal waves can be represented like transverse waves • Compressions become the crests • Rarefactions become the troughs

  6. 15.2 Properties of Waves • Amplitude: maximum distance particles of the medium move away from the rest position • Greater energy  greater amplitude • Wavelength (λ): distance between two corresponding parts of a wave • Distance crest to crest or compression to compression • Frequency (ν): number of complete waves that pass a given point in a certain amount of time • Measured in Hertz (Hz) or “per seconds” • Speed: how far a wave travels in a given amount of time

  7. Relationships Between the Properties of Waves • Speed = wavelength x frequency • Frequency = speed / wavelength • Wavelength = speed / frequency

  8. 15.3 Interactions of Waves Reflection: when an object or wave hits a surface through which it cannot pass and it bounces back Law of reflection: angle of incidence equals angle of reflection

  9. 15.3 Interactions of Waves • Refraction: bending of waves due to a change in speed when a wave enters a new medium at an angle • Diffraction: bending of waves due to movement around or through a barrier

  10. 15.3 Interactions of Waves • Interference: the interaction of waves that meet; can be constructive or destructive • Constructive interference: energies add together and amplitude is increased (higher crests and lower troughs) • Amplitude is the sum of the two original amplitudes • Destructive interference: waves subtract energies and amplitude is decreased (flatter crests and troughs) • Amplitude is the difference of the two original amplitudes • If original amplitudes were the same, crest and trough cancel each other completely

  11. Wave Interference • https://www.youtube.com/watch?v=P_rK66GFeI4

  12. 15.3 Interactions of Waves • Standing waves: interference of two waves that appears to be one wave standing in place • Destructive interference creates nodes, or points of zero amplitude • Constructive interference creates antinodes, or points of maximum amplitude • Antinodes always occur halfway between nodes • Resonance: increase in amplitude that occurs when external vibrations match an objects natural frequency • Most objects vibrate at (at least one) natural frequency • Useful for musical instruments • Destructive potential in buildings, bridges, etc.

  13. 15.4 Seismic Waves • Seismic waves: waves produced by an earthquake which carry energy through Earth • P waves: primary waves, longitudinal (compress and rarify rock in the earth), move faster than other seismic waves • S waves: secondary waves, transverse (shake ground ), cannot travel through liquids and thus are not detected on the side of the earth opposite the earthquake • Surface waves: combination of s and p waves, travel more slowly but create more severe movements • Surface waves on the ocean create tsunamis

  14. 15.4 Seismic Waves • Seismograph: instrument that records ground movements caused by seismic waves • Used to detect and measure earthquakes • Distance to earthquake can be measured by time between P and S waves • Origin of earthquake can be determined using at least three seismographs at different places on Earth • Also used to detect underground resources when explosives are set off

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