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SCIENCE ITALIAN STYLE:
Fixing the Leaning Tower of Pisa

Despite a ten-degree tilt, the Leaning Tower of Pisa has been standing for over 800 years. But Italy's most famous tourist attraction still needs serious propping up. The tower is the site of what may have been the first true scientific experiment, conducted by Galileo Galilei in the 16th century and repeated here by Frontiers host Alan Alda. Through computer animation, we see why it is critical that engineers devise a plan to keep the tower from becoming a former wonder.

Activity: Critical Lean

 HISTORY/SOCIAL STUDIES Renaissance MATH angles, geometry,trigonometry PHYSICAL SCIENCE center of balance,gravity, law of falling bodies PHYSICS gravity, stress and structure TECHNOLOGY design, engineering,materials science

ACTIVITY 1: CRITICAL LEAN

As you've seen on Frontiers, engineers and scientists are on a mission to prevent the Leaning Tower of Pisa from toppling. But instead of straightening the tower, they hope to preserve its celebrated tilt. When engineers study problematic situations such as the tilt of the Pisa tower, they often construct physical models. Here's your chance to build your own tower and measure its maximum tilt before it topples.

MATERIALS
• straws
• modeling clay
• scissors
• heavy stock cardboard
• protractor

CHALLENGE
• Build a tower using only straws and modeling clay on a piece of heavy stock cardboard that serves as a base. Raise one end of the cardboard base so that the tower tilts by 10 degrees. Measure the angle with a protractor. Wait 30 seconds, then record any change in the tower's appearance.

• Increase the base tilt by another 10 degrees. Wait 30 seconds, then record any change in the tower's appearance. Continue increasing the tilt angle by ten-degree increments, until the tower topples.

QUESTIONS
1. At what angle did the tower become unsteady?

2. How did the amount of clay used in your tower's construction affect the structure's stability? Explain.

3. How might increasing the wait time to 60 seconds affect your results? Explain.

4. If you had a ruler instead of a protractor, how would you determine the angle of the base tilt?

5. Can you improve your tower's stability? First, make a drawing of your revised design. Then, construct a new tower and determine the angle at which the structure begins to topple.

WHAT KEEPS THE LEANING TOWER OF PISA FROM FALLING OVER?

The tower's center of gravity (or mass). A structure's stability depends upon its center of gravity. Mass placed above this center may increase a tower's tilt, eventually causing the structure to topple. Mass equally distributed below this center will add stability.

ACTIVITY EXTENSIONS
• Build a "leaning tower of pasta" out of uncooked fettuccine or other pasta and modeling clay. Can you make it lean without falling?

• After you watch the Frontiers episode, can you brainstorm any other ways to correct the tower's tilt?

• All objects, including people, have a center of gravity or balance point. Where do you think yours is located?

 Scientific American Frontiers Fall 1990 to Spring 2000 Sponsored by GTE Corporation, now a part of Verizon Communications Inc.