Vibrating Rods and Plates 
Vibrating Rods and Plates
by Prof. Miller
Video Lecture 35 of 46
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Date Added: February 5, 2015

Lecture Description

A - A metal rod is held in the finger and thumg near one end - the rod in a vertical line. With a hammer we strike one end of the rod. As the position of the holding changes the pitch emitted by the bar changes. We are exciting the bar compress!onaIly - longitudinally. What it emits is governed by many things: its stuff - its geometry -where it is held. For certain positions of "damping" the bar has enormous acoustic life and very very high Q. By the Q of a system we mean - in a general way - how much energy it returns for the energy we give it. At certain positions this bar gives rise to fantastically high-pitched emission.

B - We have an array of metal plates - of different stuff - of different shape. These are called CHLADNI PLATES. They are fixed at the center to a pin rigidly bound to the plate. We bow the plate with a violin bow. It sounds. It is vibrating. But HOW? It is too fast to see. So we sprinkle it with sand or with sugar and low and behold - a WONDROUS thing arises: The sand takes up beautiful patterns - governed by how we bow the plate - where we bow the plate and so on. The beautiful figures resulting are called CHLADNI FIGURES.

C - It is rather well known that glasses and goblets can be stroked -
excited - bu rubbin a wet finger along the edge. If now we arrange a set of these - say eight - tuned with different levels of water - a delightful music can be played. And here again we have relaxation oscillations - the finger grips the edge of the glass - I ets go - and this action is repeated.

D - So too a steel drum can be shaped with a hammer - giving different shaped segments - of different size - of different thickness. The music which these emit is indeed delightful.

E - A tuning fork - say 512 vps - one octave above middle C - is struck. You hear 512 vps. Now if this fork is moved toward a distant hearer and then away from the hearer a change in pitch is noted. This is called the Doppler Effect. It plays a role in both light and in sound since it is a consequence of more waves or less waves reaching the observer per unit time. You detect this when you hear a Police siren! I

Course Index

  1. The Idea of the Center of Gravity
  2. Newton's First Law of Motion: Inertia
  3. Newton's Second Law of Motion: The Elevator Problem
  4. Newton's Third Law of Motion: Momentum
  5. Energy and Momentum
  6. Concerning Falling Bodies & Projectiles
  7. The Simple Pendulum and Other Oscillating Things
  8. Adventures with Bernoulli: Bernoulli's Principle
  9. Soap Bubbles and Soap Films
  10. Atmospheric Pressure
  11. Centrifugal Force and Other Strange Matters
  12. The Strange Behavior of Rolling Things
  13. Archimedes' Principle
  14. Pascal's Principle: The Properties of Liquids
  15. Levers, Inclines Planes, Geared-wheels and Other Machines
  16. The Ideas of Heat and Temperature
  17. Thermometric Properties and Processes
  18. How to Produce Heat Energy
  19. Thermal Expansion of Stuff: Solids
  20. Thermal Expansion of Stuff: Gases & Liquids
  21. The Strange Thermal Behavior of Ice and Water
  22. Heat Energy Transfer by Conduction
  23. Heat Energy Transfer by Convection
  24. Heat Energy Transfer by Radiation
  25. Evaporation, Boiling, Freezing: A Dramatic Adventure
  26. Miscellaneous Adventures in Heat
  27. The Drama in Real Cold Stuff: Liquid Nitrogen
  28. The Physics of Toys: Mechanical
  29. The Physics of Toys: Acoustic and Thermal
  30. Waves: Kinds of Properties
  31. Sound Waves: Sources of Sound & Pitch and Frequency
  32. Vibrating Bars and Strings: The Phenomenon of Beats
  33. Resonance: Forced Vibrations
  34. Sounding Pipes
  35. Vibrating Rods and Plates
  36. Miscellaneous Adventures in Sound
  37. Electrostatic Phenomena: Foundations of Electricity
  38. Electrostatic Toys, Part 1
  39. Electrostatic Toys, Part 2
  40. Adventures with Electric Charges
  41. Adventures in Magnetism
  42. Ways to "Produce" Electricity
  43. Properties and Effects of Electric Currents
  44. Adventures in Electromagnetism
  45. Further Adventures in Electromagnetism
  46. Miscellaneous and Wondrous Things in E&M

Course Description

Demonstrations in Physics was an educational science series produced in Australia by ABC Television in 1969. The series was hosted by American scientist Julius Sumner Miller, who demonstrated experiments involving various disciplines in the world of physics. The series was also released in the United States under the title Science Demonstrations.

This program was a series of 45 shows (approximately 15 minutes each) on various topics in physics, organized into 3 units: Mechanics; Heat and Temperature / Toys; and Waves and Sound / Electricity and Magnetism.


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