# What Is an Application of Charles' Law?

One application of Charles' Law is a hot air balloon. Hot air balloons rise when the air inside them is heated by a torch, which causes particles to move rapidly and then disperse.

Charles' Law is named after Jacques Charles, who was a balloonist living in the 1700s. Charles studied the relationship between the volume of gases and temperature to help get balloons to rise. Charles conducted a series of these experiments in 1787, but they were never officially published. Charles is credited with setting the first hydrogen-powered balloon afloat above Paris, France, in 1783. In honor of his achievements, Charles' Law bears his name. Charles' Law explains that the volume of gas in a given area increases as a gas is heated and its pressure remains constant. Similarly, Charles' Law states that a decrease in temperature results in a decrease of gas.

Applications of Charles' Law
Hot air balloons, which rely on heated fuels to rise, are one application of Charles' Law. When gas particles in a hot air balloon are heated, they spread out and move more quickly, which means that the gases expand and take up more space. This increase in activity creates the energy that balloons need to rise off the ground as the balloons become less dense than the air around them. The decrease in the balloon's density causes it to float, and conversely, a rise in the balloon's density leads to it deflating and returning to the ground.

Hot Air Balloon Composition
Most hot air balloons are made of nylon. This fabric is lightweight and is generally reinforced with polyurethane, which makes balloons airtight and helps protect them from the sun's damaging ultraviolet (UV) rays. Hot air balloons rise when the air in the nylon bag, or envelope, is heated. Balloons descend when the air from the envelope is vented out from the top. Balloons have a relatively simple construction. They are operated using just an altimeter that measures altitude, a temperature gauge and a rate-of-climb envelope. Hot air balloons vary in size. Sport balloons, which are the most common and popular variety, have a diameter of 55 feet, and they are about 70 feet tall, which equates to about seven stories tall. Sport balloons are made with about 1,075 square yards of nylon. This translates to over three miles of nylon fabric. About a half-mile worth of reinforced material is used to hold the envelopes securely together. Sport balloons, when inflated, can hold over 62,000 bushels of apples and just under 580,000 gallons of water. Hot air balloons can carry three to four people.

How Hot Air Balloons Work
Balloons are ignited with liquid propane gas, or LPG. Their fuel supplies are either divided between two tanks or three tanks. Balloons with two tanks carry 40 gallons of fuel, which is divided between two 20-gallon tanks. Smaller balloons carry 30 gallons of LPG, which is distributed among three tanks that carry 10 gallons each. Propane is selected as a fuel choice because it burns rapidly and efficiently, but it is also predictable and stable. Balloons carry LPG in liquid form, and LPG is fed through hoses to ignite the balloons. Over a flight time of 45 minutes to one hour, balloons will burn approximately 20 to 30 gallons of fuel. For safety, many balloons are also equipped with an independent fuel system that can operate the balloon if the primary fuel system runs out or fails.

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