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The Physics of Resonance

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Introduction

Resonance is a common thread which runs through almost every branch of physics, and yet a lot of people have never studied it. Without resonance we wouldn't have radio, television, music, or swings on playgrounds, not to mention cool gismos like Tesla coils. Of course, resonance also has its dark side. It occasionally causes a bridge to collapse, a helicopter to fly apart, or other inconveniences. Unlike black holes, time travel, and quantum mechanics, resonance is common place and easy to observe. Yet, it is one of the most striking and unexpected phenomenon in all of physics.

The following site is the most comprehensive site on resonance available on the web. Its information is intended especially for use by high school students, teachers, home schools, and anyone interested in the subject. Suggestions for quick demos are included in many of the sections and are noted on the contents page. More elaborate demos and lab experiments are described in separate sections which contain the word demonstration in the title.

The materials and parts specified in the demonstrations are based on items commonly found in the United States since that is where the demonstrations were built and tested. However, we sincerely hope our international readers will be able to gain some useful ideas.

Resonance Basics
Nikola Tesla - Master of Resonance: Tesla was a genius who was obsessed with resonance. No discussion of resonance could be complete with out talking about Tesla.
 
The ABC's of Resonance: Find out what resonance is and why it happens.
 
Vibrations/Oscillations
Playground Swings: This is the example Tesla used when he gave explanations of resonance. (Demo)
 
Sound
An Incredibly Irritating Resonance Demonstration: This easy-to-do demo creates an unexpected, incredibly ear splitting, and annoying sound. It's one of the most dramatic high school physics demos available.
Electrical/Magnetic Resonance--at the foundation of wireless communication.
 
Electrical Circuits Anything which moves can potentially resonate, even the electrons in a circuit.

Crystal Radio Demonstrations Crystal radios are simple circuits designed to resonate at the same frequency as the radio station they're tuned to receive.

How Antennas Work You guessed it. They resonate (at least the most efficient ones do).

Standing Electrical Waves Demonstration Actually see standing electrical waves using an ordinary florescent tube.

Antenna Demonstrations Shows that simple antenna's work best when their length is adjusted so that they resonate. Also shows that simple antennas emit polarized waves.

For more information about wireless communication and the electromagnetic spectrum visitThe Hidden World of the Electromagnetic Spectrum.

Appendix
References
The Dark Side of Resonance, 
The Tacoma-Narrows Bridge 

Every powerful phenomenon in nature has its dark side and resonance is no exception. It's best experienced in moderation. Taken to an extreme, resonance causes things to break catastrophically. For example, when an opera singer with a very loud voice hits the right frequency she can cause a champagne glass to resonate and break. 

On the morning of November 7, 1940, the four month old Tacoma Narrows Bridge began to oscillate dangerously up and down. A reporter drove out on the bridge with his cocker spaniel in the car. The bridge was heaving so violently that he had to abandon his car and crawl back to safety on his hands and knees.

At about 11:00 the bridge tore itself apart and collapsed. It had been designed for winds of 120 mph and yet a wind of only 42 mph caused it to collapse. How could this happen? No one knows exactly why. However, the experts do agree that somehow the wind caused the bridge to resonate. It was a shocking calamity although the only loss of life was the cocker spaniel.

View NOVA videos of the collapse. (Follow the link and scroll down to the bottom of the page)

   
Acknowledgements
Parts of this project were supported by a National Science Foundation Research Experience for Teachers grant as part of Clemson University's Summer Undergraduate Research Experience in Wireless Communications.
 
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