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Name: Rebecca G.
Status: student
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Question:
How do molecules in the air cause air resistance?



Replies:
Basically, the air molecules just get in the way. Imagine walking through a crowded room. You have to push people aside or wait for them to move out of your way. You are forced to move very slowly. Now imagine moving through an empty room. You can just walk straight where you want to go. When an airplane or car or ball moves through the air, the air molecules get in the way, and have to be moved aside -- like moving through a crowded room. Just like it takes some energy (some force) to move the people aside, the air molecules also take a force to be moved aside. This is the air resistance you feel.

I hope this helps,

Burr Zimmerman


Rebecca,

For an object to pass through air in any direction (running, falling, flying ...), the object must push the air molecules out of the way. There is always some push from the air, called air pressure. This is what astronauts have to worry about when in space. This is why they have pressure suits. When moving air molecules out of the way, the object pushes harder than usual. When the object pushes harder on the molecules, the molecules push back harder. This extra push from the air molecules is air pressure. The faster the object moves, the faster it must push air molecules out of the way. This is why air pressure gets stronger when an object moves faster through the air.

Dr. Ken Mellendorf
Physics Instructor
Illinois Central College


Dear Rebecca G.,

An object, say a baseball, travelling through the air will, of course, collide with all the molecules in its path. Each molecule will be pushed forward by the collision and so will exert a backward force on the baseball.

Since each molecule is so tiny and so light each collision exerts a very small force on the baseball, but since there are so many molecules the combined effect can cause an appreciable amount of air resistance.

Best, Dick Plano, Professor of Physics emeritus, Rutgers University


Air is a mixture, mostly of nitrogen and oxygen molecules. These molecules "get in the way" of an object trying to move through the air. To move through the air, the object has to "push" the air out of the way. The molecules "push back". You can think of this like a person trying to "push" through a crowd. In order to move forward, the person has to move the "crowd" out of the way. The more people in the crowd, the more resistance there is for the person to move through the crowd. While not an exact example, it does describe the basic idea of the resistance of the movement of the molecule trying to move through the atmosphere.

Vince Calder



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