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Air Resistance - Friction of a gas! Friction is the force between two surfaces rubbing together - Air resistance is the frictional force between an object and the air it is moving through. It is due to the collision of the object with millions of molecules of air. A falling object collides with air molecules during its downward fall. A speeding object collides with air molecules as it hurtles along. These air molecules experience a change in momention, creating a force pushing in a direction which is opposite to the object's direction of travel - this is called 'drag'.
The amount of air resistance or drag encountered by the object depends on three factors:1: Speed The faster it moves the more air particles it collides with per second therefore the bigger the air resistance will be. If it is not moving the air resistance would be zero. 2: The area of intercept The area of intercept is the cross section of the object (perpendicular to the direction of travel). The larger this is the more air particles it will bump into per second and the higher the air resistance will be. If the object is very streamlined the area of intercept will be small and there will be less air resistance than if it was bulky with lots of areas that could trap pockets of air as it travelled. 3: The air density The greater the density of the air (it is less dense at higher altitudes - the air is said to be 'thinner') the more air particles the object will bump into each second making the air resistance greater.
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