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Floating festival: pilots compete and blow away audiences at the world's largest hot-air-balloon festival.

Each fall, huge crowds gather at dawn to watch hundreds of hot-air balloons take to the skies over Albuquerque, New Mexico. The balloons tower up to eight stories high and come in an array of colors and shapes, from traditional round balloons to ones shaped like a panda, a space shuttle, and a football. The spectacle kicks off the Albuquerque International Balloon Fiesta.

Hot-air-balloon pilots from around the globe go to the Fiesta to show off not only their lighter-than-air crafts, but also their flying abilities. They do this by competing in a series of challenges where they attempt to snatch prizes off supertall poles and rack up points by dropping markers onto targets below. To win, balloonists need both skill and science on their side.

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LIFTOFF

Teams launch from sites at least one mile from the challenge field. There, they ready their balloons by switching on a propane burner fitted atop the passenger basket. The burner shoots a flame into the opening at the bottom of the balloon, heating the air inside.

As the temperature increases, the air's density (mass per unit volume) changes: The air molecules move faster and spread farther apart. This provides the buoyant force (upward force on an object immersed in a gas or liquid) needed for the balloon to float. "The balloon rises because the hot air inside the balloon is less dense than the surrounding air," explains Rebecca Thompson-Flagg, a physicist at the American Physical Society in College Park, Maryland.

If a pilot switches off the flame and allows the air inside the balloon to cool, the balloon will slowly sink. For a faster descent, the pilot can open vents at the top of the balloon to release the hot air.

RIDING THE WIND

Once it's aloft, there's only one way to navigate a hot-air balloon. "The trick is to find a wind current in the direction you want to go," says Ray Bait, a hot-air-balloon pilot and Fiesta president.

Winds blow in different directions at different altitudes. So before heading out, teams release a helium-filled party balloon and use compasses and stopwatches to monitor its movement as it rises. They use this information, along with weather reports, to map out a potential flight path.

Balloonists at the Fiesta also take advantage of a unique wind pattern called the "Albuquerque Box." The Rio Grande River Valley and surrounding mountains cause winds to blow in a southerly direction near the ground and in a northerly direction higher up. This allows pilots to move in a vertical box back and forth across the Fiesta grounds, which cover an area the size of 54 football fields (see Nuts & Bolts, below).

GAME ON

As they drift toward the challenge site, balloonists try their best to aim their crafts toward a single point on the ground. In the target contest, pilots set their sights on a giant "X." Then when the moment is right, they drop a beanbag marker. "The goal is to get the marker as close to the target as possible," says Bair.

An even tougher task is the prize grab. Pilots have to maneuver within arm's reach of five envelopes perched atop 9 meter (30 foot)-tall poles. Balloons bump into one another as pilots jostle to snatch the envelopes filled with mystery prizes like cash or keys to a new car.

"The people who do the best at competitions are the ones who know the subtleties of the wind," says Bair. That, and a bit of luck, makes all the difference between success and just a lot of hot air.

nuts & bolts

WIND POWER

Hot-air-balloon pilots at the Albuquerque International Balloon Fiesta can take advantage of a weather pattern known as the "Albuquerque Box." This special set of winds allows balloonists to make multiple passes over the competition field.

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PRE-READING PROMPTS:

* What force allows a hot-air balloon to float?

* How do balloonists get their vehicles to rise, fall, and move from side to side?

* What do you think it would be like to compete in a hot-air-balloon contest?

DID YOU KNOW?

* The Energizer Bunny's Hot "Hare" Balloon is the world's tallest hot-air balloon, measuring 51 meters (166 feet), which is 4.5 m (15 ft) taller than the Statue of Liberty.

* According to legend, the first hot-air balloon was the Kongming lantern that was used by 3rd-century Chinese military leader Zhuge Liang. He built the balloons out of rice paper, bamboo, and a candle. He then launched them into the sky to signal his armies.

* The first piloted hot-air-balloon flight occurred on November 21, 1783, in Paris, France.

CRITICAL THINKING:

* While most hot-air balloons use the buoyancy created by heated air to launch their aircrafts, another type of balloon uses lighter-than-air gases, such as helium, to achieve liftoff. What are some advantages and disadvantages to each of these methods of producing lift? Which aircraft would you prefer to pilot?

PROJECT-BASED LEARNING:

LANGUAGE ARTS: Jules Verne's novel Around the World in Eighty Days is the adventurous tale of Phileas Fogg, who is challenged to circumnavigate the globe in a hot-air balloon in 80 clays. Write your own adventure story that is based upon a trip you take in a hot-air balloon. Be sure to describe what you do to take off, navigate, and land your balloon in addition to the tales of your travels.

RESOURCES

You can access these Web links at www.scholastic.com/scienceworld.

* Test your hot-air balloon piloting skills with this interactive game at Southern Florida's Sun Sentinel's Web site:

www.sun-sentinel.com/broadband/theedge /sfl-edge-balloongame,0,843241.flash.

* Learn more about the physics of hot-air balloons with this video produced by Colorado State University:

http://littleshop.physics.colostate.edu/Videos /Sinking&Floating/hotairballoons/hotairballoons.html.

* For more information about the Albuquerque International Balloon Fiesta, visit: www.balloonfiesta.com.

CHECK FOR UNDERSTANDING

DIRECTIONS: Below are the steps commonly used to launch a hot-air balloon. Read each sentence, and then place the letters of the sentences in the order in which they occur from first to last.

a. The buoyant force grows as the warm air inside |he balloon becomes less dense.

b. Flames from the propane burner heat the air inside the balloon.

c. Liftoff!

d. Air molecules inside the balloon begin to move faster and spread farther apart as they heat tip.

e. The pilot turns on the propane burner.

Answers

e, b, d, a, c
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Title Annotation:PHYSICAL: BUOYANCY
Author:Crane, Cody
Publication:Science World
Geographic Code:1USA
Date:Feb 20, 2010
Words:1069
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