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Vibrations and Waves

Vibrations and Waves. Vibrations. A vibration is any kind of repeated motion which can be described by: Amplitude: Frequency: Period: All objects have frequencies they like to vibrate at called. Vibrations. A vibration is any kind of repeated motion which can be described by:

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Vibrations and Waves

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  1. Vibrations and Waves

  2. Vibrations • A vibration is any kind of repeated motion which can be described by: • Amplitude: • Frequency: • Period: • All objects have frequencies they like to vibrate at called

  3. Vibrations • A vibration is any kind of repeated motion which can be described by: • Amplitude: A = Distance from equilibrium [m] • Frequency: f = # of cycles/second [Hz] • Period: T = seconds/cycle [s] • All objects have frequencies they like to vibrate at called natural frequencies

  4. Parts of a Wave

  5. Parts of a Wave

  6. Waves They are described by:

  7. Waves • A wave is a disturbance that travels through a medium carrying energy. They are described by: • Amplitude (A) • frequency (f) • period (T) • wavelength () [distance of one cycle]

  8. There are 2 kinds of waves: • Transverse: • Longitudinal:

  9. There are 2 kinds of waves: • Transverse: Disturbance (vibration) perpendicular to motion of the wave • Longitudinal: Disturbance (vibration) parallel to the motion of the wave

  10. Longitudinal wave: the particles vibrate parallel to the direction of motion of the wave. Transverse wave:the particles in the medium vibrate at right angles to the direction in which the wave travels

  11. T = period [s] • ∆t = duration [s] • f = frequency [Hz] • N = number of vibrations

  12. The Universal Wave Equation • All waves (longitudinal and transverse) obey the same equation that relates the wavelength ( in m) frequency (f in Hz) and speed (v in m/s)

  13. Pg. 445. Dolphins have a large repertoire of sounds that can be classified under two general types: those sounds used to locate objects, termed echolocation (sonar), and those emitted to express emotional states. Dolphins emit pulses and clicks in groupings at a rate of over 690 clicks per 2.3 s. The sounds have a frequency of typically 130 kHz • a) Find the period and frequency of emission of pulses. • b) Given that the speed of sound is 344 m/s, find the wavelength of the emitted pulse.

  14. An FM station, BOOM, broadcasts radio signals with a frequency of 97.3 MHz. These radio waves travel at a speed of 3.00 × 108 m/s.What is their wavelength?

  15. Properties of Waves

  16. Transmission • Transmission: When a wave passes from one medium to another medium • Refraction:  changes and the wave seems to “bend” at the boundary • Diffraction: When a wave passes through an opening <  the wave spreads out

  17. Reflection • A wave can also be reflected back at a boundary • When v1 < v2 (free end) the wave is reflected back with no phase change • When v1 > v2 (fixed end) the wave is reflected back with a phase change • At any boundary there can be a mix of reflection and transmission

  18. Wave travelling from fast to slow medium Wave travelling from slow to fast medium

  19. Interference • Interference is the result of two or more waves meeting at a point in space and time • The principal of superposition states that the resultant wave is the vector sum of the waves that are coming together • Constructive Interference: New amplitude is larger • Destructive Interference: New amplitude if smaller

  20. Destructive interference Constructive interference

  21. Constructive interference Destructive interference

  22. Interference and Resonance

  23. Standing Waves • The distance between nodes dn is:

  24. Standing Waves • A standing wave is formed when two identical waves traveling in opposite directions interfere • A node is a point that does not vibrate • An antinode is a “supercrest/trough” • The distance between nodes dn is:

  25. Draw a scale diagram of a standing wave pattern on an 8.0-m rope with four antinodes between the ends. What is the wavelength of the waves that produced the pattern?

  26. Ex. A standing wave has a distance of 45 cm between four consecutive nodes. What is the wavelength of the wave? What is the speed of the wave in the medium if the frequency of the source is 30 Hz?

  27. Resonance

  28. Resonance • All objects have a natural frequency they like to vibrate at (sets up standing waves) • Mechanical Resonance is the vibrating response of an object to a periodic force that has the same frequency as the natural frequency of the object

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