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Waves

Introduction, Wave Equation, Interference & Standing Waves. Waves. What is a wave?. Waves are disturbances that transfer energy from one point to another in a medium Particles of water or air vibrate, but do not actually move forward with the wave. A Transverse Wave. A Longitudinal Wave.

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Waves

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  1. Introduction, Wave Equation, Interference & Standing Waves Waves

  2. What is a wave? • Waves are disturbances that transfer energy from one point to another in a medium • Particles of water or air vibrate, but do not actually move forward with the wave • A Transverse Wave • A Longitudinal Wave How does the vibration of particles in a transverse and a longitudinal wave compare?

  3. What is a wave? • A Transverse Wave • Show the direction of wave propagation • Watch the motion of a single particle. Label the direction of particle vibration. • Particles vibrate _________________ to wave propagation. • Eg. Water waves • Also see pg. 336, Figure 7.7

  4. What is a wave? • A Longitudinal Wave • Show the direction of wave propagation • Watch the motion of a single particle. Label the direction of particle vibration. Particles vibrate ________________ to wave propagation. Eg. Sound waves • Also see pg. 336, Figure 7.7

  5. Vocabulary • Periodic motion • Repeated motion over regular time intervals • Cycle • One complete repeat of the pattern • Period (T) • Time required to complete one cycle • Frequency (f) • No. of cycles completed in a time interval • Measured in Hertz (Hz), 1 Hertz = 1 cycle/ second * Period and frequency are related:

  6. Vocabulary • Amplitude (A) • Distance from rest position to maximum displacement Eg. Label the amplitude of the waves below:

  7. Vocabulary • Phase difference • Used when comparing two different waves • Two waves are in phase when they are moving in the same direction at the same time Eg. Which pair of pendulums are in phase?

  8. Vocabulary • Wavelength (λ) • Shortest distance betweentwo points that are in phase • Crest • Highest point on a wave • Trough • Lowest point on a wave

  9. Natural Frequencies & Resonance • An object allowed to vibrate freely, like a pendulum, will vibrate at a specific frequency called its natural frequency. • How does this relate to natural frequency? • When an object is vibrated at its natural frequency, the amplitudes of vibration will become very large. This is known as resonance. • How does this relate to resonance?

  10. Natural Frequencies & Resonance • The Tacoma Narrows Bridge collapsed on Nov. 7, 1940 due to moderate winds of 60 to 70 km/h. • How is this event related to natural frequency & resonance? • Link to video 1 (*.mov), link to video 2 (YouTube).

  11. Natural Frequencies & Resonance • Other examples of natural frequencies & resonance: • A child on a swing • Shattering glass with sound • Treatment for gall & kidney stones • How would you explain how these are related to natural frequencies & resonance?

  12. The Wave Equation • The speed of any wave in a medium is independent of wave size, or the amount of energy it carries. • Speed of sound in air (at 0˚C) is 331.4 m/s • Speed of sound in steel is 4512 m/s • To measure & calculate the speed of a wave: v = fλ v = speed of wave (m/s) f = frequency (Hz) λ = wavelength (m) Can you come up another version of the wave equation?Hint:

  13. Practice • P. 387 # 1- 5

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