Vibrating Rods and Plates
by
Video Lecture 35 of 46
Not yet rated
Views: 799
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 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.

## Comments

There are no comments. Be the first to post one.
 Post comment as a guest user. Click to login or register: Your name: Your email:(will not appear) Your comment:(max. 1000 characters) Are you human? (Sorry)