Why do Hot Air Balloons Fly
How the Ideal Gas Law and Archimedes's Principle Apply to Ballooning
Nov 10, 2008 Paul A. Heckert
Two fundamental principles of physics govern hot air balloon flight. They are not the same principles that govern airplane flight.
At a hot air balloon festival, hot air balloons slowly fill and then rise majestically in the predawn sky. These hot air balloons fly because of two fundamental principles of physics: the ideal gas law and Archimedes's principle.
Ideal Gas Law
The ideal gas law is a mathematical relationship between the volume pressure and temperature of a gas. For a given quantity of gas, the pressure, P, multiplied by the volume, V, divided by the temperature, T, remains a constant.
If a gas is heated, as in a hot air balloon, then its volume will increase. A heater in the balloon's basket heats the air inside the balloon and blows hot air into the balloon. As the volume of gas increases, it fills the balloon. Soon the balloon is full of hot air. If the air continues to heat up, it expands and flows out of the hole in the bottom of the balloon.
Hence a balloon filled with hot air contains fewer air molecules than the same balloon inflated to the same size with cool air. A hot air balloon will therefore be less dense than a balloon filled with cool air as a consequence of the ideal gas law.
Archimedes's Principle
Archimedes's principle states that when an object is suspended in a fluid, the buoyant force acting on an object is equal to the weight of the fluid displaced. As a consequence of Archimedes's principle, an object will float in a fluid if it is less dense than the fluid.
The article provided was found form the website (http://physics.suite101.com/article.cfm/why_do_hot_air_balloons_fly)
"In a hot air balloon it is filled with hot air that is less dense that when it is filled with cool air. For the hot air balloon to rise and carry the basket of passengers the balloon mush have a low density. This relates to the terminology we took on density. All together the balloon the basket and its passengers must weigh less than the total amount of air displaced by the balloon or it won't rise. When it does weigh less then the air in the balloon there is an upward buoyant force which exceeds the downward weight. This is the same princle that of helium balloons because the helim gas is much less dense than air."
How the Ideal Gas Law and Archimedes's Principle Apply to Ballooning
Nov 10, 2008 Paul A. Heckert
Two fundamental principles of physics govern hot air balloon flight. They are not the same principles that govern airplane flight.
At a hot air balloon festival, hot air balloons slowly fill and then rise majestically in the predawn sky. These hot air balloons fly because of two fundamental principles of physics: the ideal gas law and Archimedes's principle.
Ideal Gas Law
The ideal gas law is a mathematical relationship between the volume pressure and temperature of a gas. For a given quantity of gas, the pressure, P, multiplied by the volume, V, divided by the temperature, T, remains a constant.
If a gas is heated, as in a hot air balloon, then its volume will increase. A heater in the balloon's basket heats the air inside the balloon and blows hot air into the balloon. As the volume of gas increases, it fills the balloon. Soon the balloon is full of hot air. If the air continues to heat up, it expands and flows out of the hole in the bottom of the balloon.
Hence a balloon filled with hot air contains fewer air molecules than the same balloon inflated to the same size with cool air. A hot air balloon will therefore be less dense than a balloon filled with cool air as a consequence of the ideal gas law.
Archimedes's Principle
Archimedes's principle states that when an object is suspended in a fluid, the buoyant force acting on an object is equal to the weight of the fluid displaced. As a consequence of Archimedes's principle, an object will float in a fluid if it is less dense than the fluid.
The article provided was found form the website (http://physics.suite101.com/article.cfm/why_do_hot_air_balloons_fly)
"In a hot air balloon it is filled with hot air that is less dense that when it is filled with cool air. For the hot air balloon to rise and carry the basket of passengers the balloon mush have a low density. This relates to the terminology we took on density. All together the balloon the basket and its passengers must weigh less than the total amount of air displaced by the balloon or it won't rise. When it does weigh less then the air in the balloon there is an upward buoyant force which exceeds the downward weight. This is the same princle that of helium balloons because the helim gas is much less dense than air."
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