Liberty Bell

Podcast

Liberty Bell

Transcript

Letting freedom ring, again. I'm Bob Hirshon and this is Science Update.

After the founding fathers of America signed the Declaration of Independence in 1776 - They rang the Liberty Bell. And the bell kept tolling for all important events until it cracked in 1846.

But now, you can hear how the bell may have sounded before the nasty fissure, and how it would sound if you rang it today.

That's thanks to work by mechanical engineer Gary Koopman at the Center for Acoustics and Vibration at Penn State. He and his students have created a virtual Liberty Bell.

Koopman:
"This is a computer model and we could actually observe the bell, the various shapes that the bell would vibrate in the various patterns that would give you each tone."

Here's what the Liberty Bell probably sounded like back in 1776.

And here's the computerized bell with a crack.

Doctor Koopman's main focus is understanding the sounds that different materials generate in an effort to design quieter buildings. He and his students created the virtual Liberty Bell as an exercise, and a way to celebrate the year 2000.

For the American Association for the Advancement of Science, I’m Bob Hirshon.

Making Sense of the Research

One of the most powerful tools used by scientists and engineers is the computer. One way they use computers is to create "models" or "simulations" of objects or phenomena. By examining these models, scientists can often learn things about the real world. Scientists use computers to create simulations of ocean currents, weather patterns, or the progression of a disease in the human body. Engineers create models of airplanes that exist only on the computer screen, but that can be tested almost like real airplanes.

In this Science Update you learned that researchers have created a model of the famous Liberty Bell, so that they can study the bell's structure and even hear what it sounds like -- all without leaving the lab. This story can serve as a jumping off point for discussions of other kinds of models, or the creation of an actual model. You should understand the strengths and limitations of their models and the tests performed on them.

Now try to answer the following questions:

1. What aspects of the Liberty Bell are Dr. Koopman and his students able to observe using the virtual Liberty Bell?
2. How many different tones does the Liberty Bell have?
3. Listen to the Real Audio version of what the bell probably sounded like back in 1776. Describe the sounds you hear.
4. Listen to the Real Audio version of the computerized bell with a crack. What does is sound like?
5. Are there any differences between the way the bell probably sounded in 1776 and the computerized bell with the crack?
6. Why did Dr. Koopman and his students create the virtual Liberty Bell?
7. For what other purposes might scientists create and use computer models?

Going Further

As an extension to this Science Update, go to the Vocal Vowels exhibit on the Exploratorium website. This interactive exhibit shows how hollow plastic models of the human vocal tract can turn the squawk of a duck call into vowel sounds.

For practice with creating models, go to the Discovery Channel School online activity, Animating Motion. Be sure to check out the other activities on this site, such as Understanding: Bridges.