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"Let us strive to make each moment beautiful."
Saint Francis DeSales
painting by Katie Bergenholtz

Ben Franklin, Sound and Mapping Ocean Currents

Previous posts: Young Ben Franklin,  Ben Franklin and Electricity)


1762 Mapped Postal Routes in the colonies. Invented Glass Armonica
Have you ever made sounds with a glass and some water? Moisten a finger with water and rub it evenly around the top of a glass to make a ringing sound.
Ben Franklin designed a version of this called the glass armonica. This instrument had a row of glass bowls mounted on a long axle attached to a wheel. The lower half of the bowls rested in water. The player used the fingers of both hands to rub the wet glasses as they turned.
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Wavelength and Sound
The wavelength of sound waves has a dramatic effect on how we hear the sound. This demonstration shows the effect.

Take a glass or plastic bottle. Glass is best and larger bottles are better. Hold the bottle up to your mouth so that the top edge of the bottle opening just touches your bottom lip. Pursing your lips, blow across the top of the bottle. It takes a little practice, but you should be able to produce a deep, low sound like a horn.
Now fill the bottle 3/4 the way full of water and blow across the opening as before. How is the sound different? The sound should be much higher now.
Wavelength is the distance between the top or crest of a wave to the crest of the next wave (or the distance between the bottom or troughs.)The wavelength of the sound wave produced was determined by how far the air could travel up and down the bottle. When the bottle was empty, air could travel all the way to the bottom of the bottle, producing sound waves with a long wavelength. When the bottle had lots of water in it, there wasn't much distance over which air could travel. As a result, the waves produced had a small wavelength.
Sound waves with large wavelengths have small frequencies and low pitches whereas sound waves with small wavelengths have large frequencies and high pitches.

The Amplitude of a Sound Wave
Make a simple stringed instrument by stretching rubber bands around a cardboard box with a hole cut in the center of one side. You could also use a plastic tub.
Watch the strings and listen to the sound as  you pluck them. First pluck lightly, and then harder. Did you notice that the harder you pluck the stings, the more they vibrate and the louder the sound?

The Ear



The model of the ear from The Body Book by Donald Silver, is almost 3-D, and yet it still folds up flat to place in a folder. The first layer shows the outer ear. The second layer shows that the ear drum is at the end of the ear canal. The hammer, anvil and stirrup bones are next, attaching at the other end to to an opening in the cochlea. You can easily visually trace sound vibrations as they pass through the parts of the ear and to the auditory nerves which send the signals to the brain with this model.


















More about sound...What Things Affect Sound?
Make Your Own Violin (craft tutorial)
The Medium Through Which Sound Waves Travel

Ben Franklin and Mapping Ocean Currents
Ben Franklin observed that mail sent by ship from America to England arrived two weeks sooner than the mail sent by ship from England to America. He began to form theories as to why this was. Perhaps the English sailors were not as good, or maybe the American ships were better built. He and a Nantucket sea captain, Timothy Folger determined that a strong current in the Atlantic Ocean helped speed American ships eastward toward England, but the same current slowed down the westward trip. Franklin drew maps of the ocean current and called it the Gulf Stream. He told the mail carrying ships how to take advantage of the Gulf Stream currents on their trips to England and how to avoid this current on their trips to America.
More about Ocean Currents.

1 comment:

  1. Hmmmm, this must be one of the posts I accidentally deleted from my reader. Either way it's a wonderful post and way to learn about sound waves.

    Whenever I think about the glass music, I think of the scene from the Sandra Bullock movie where she's an FBI agent, so funny.

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