Air Drag

How Stuff Works

When anything is moving in the air, there is a resistive force of the air pushing back. This is known as Air Drag. On the picture above, air drag is represented by the letter 'D'. Air drag is dependent on a few factors such as the density of air, area of the air plane and the drag coefficient. This is the equation for air drag:
R=(1/2)DpAv^2

For the equation, the different parts are:
R=resistive force
D=drag coefficient
p=density of the air
A=cross sectional area of object
v=velocity

If we crumpled up a paper airplane into a ball and dropped it from the top of a building and there was wind, we could look at the forces on the crumpled airplane as the downward force of gravity and the opposite force of air resistance. Because the force of gravity is equal to the mass times gravity (Fg = mg) we can add the forces on the ball into the equation:
F = mg - (1/2)DpAv^2

Air resistance plays a large part in the flight of paper airplanes by limiting the flight distance. If the air resistance was too high, the paper airplane wouldn't go anywhere. It would be like trying to throw a paper airplane under water. The design of a paper airplane revolves somewhat around the air resistance and the attempt to lessen the cross sectional area of the paper airplane. The less area that is perpendicular to the horizontal path of the airplane the less ressistance will be experienced.