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Ch. 11, Vibrations and Waves

Ch. 11, Vibrations and Waves. A repeated motion, like the pendulum on a clock, is called periodic motion . Another exp is a mass on a spring. At the equilibrium position, the speed is at its maximum. At the equilibrium position, the acceleration is zero.

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Ch. 11, Vibrations and Waves

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  1. Ch. 11, Vibrations and Waves

  2. A repeated motion, like the pendulum on a clock, is called periodic motion. • Another exp is a mass on a spring.

  3. At the equilibrium position, the speed is at its maximum. • At the equilibrium position, the acceleration is zero.

  4. At maximum displacement, spring force and acceleration reach a maximum.

  5. In an ideal system, the spring would go back and forth forever. • Friction causes a damping force that causes an oscillator to stop.

  6. In simple harmonic motion (SHM), restoring force is proportional to displacement.

  7. Hooke’s Law • Felastic = -kx • Negative sign indicates that the direction of the spring force is always opposite the direction of the displacement.

  8. SHM takes place back and forth along the same path.

  9. A stretched or compressed spring has elastic potential energy. • This can be released as kinetic energy.

  10. Pendulums • Contain a mass called a bob, attached to a fixed string.

  11. The restoring force on a pendulum is a COMPONENT of the bob’s weight. • The net force acting on a bob is Fg,x = Fg*sin(theta)

  12. As long as a pendulum stays within an angle of about 15 degrees, it is a very good example of SHM.

  13. When is Vel and Acc greatest? 0?

  14. Page 374, Figure 5, Gravitational Potential increases as a pendulum’s displacement increases. • Table 1, page 375.

  15. Amplitude The maximum displacement from the equilibrium position.

  16. Period the time to make one complete cycle.

  17. The number of cycles per unit time = Frequency. Unit = s-1

  18. f = 1/T or T = 1/f • T = 2*pi*(L/9.81)^.5

  19. Mass-Spring system in SHM • Give equation.

  20. WAVES • What are Waves? Discussion

  21. A wave is the motion of a disturbance.

  22. The MEDIUM is the physical environment through which a wave travels.

  23. Most waves are called Mechanical Waves. They need a medium to travel through. • Some waves do not require a medium, like electromagnetic radiation waves.

  24. Pulse Wave: One wave • Periodic Wave: Continuous waves

  25. Sine waves describe particles vibrating with SHM.

  26. If you look at one point, it goes up and down with SHM.

  27. Transverse waves The particles vibrate perpendicularly to the direction the wave is traveling.

  28. A Waveform can show what a wave is doing.

  29. Trough A low point • Crest A high point • Wavelength (lambda)  Distance between a whole cycle.

  30. Longitudinal Wave The particles vibrate PARALLEL to the wave’s motion.

  31. Graph = Density vs. Displacement

  32. Frequency = number of complete waves that pass a certain point per second. • Period = How long it takes ONE wave to pass a certain point.

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