Newtonian Gravitation
The Free High School Science Texts: A Textbook for High School Students Studying Physics
Main Page - << Previous Chapter (Collisions and Explosions) - Next Chapter (Pressure) >>
Properties - Mass and Weight - Normal Forces - Comparative Problems - Falling Bodies - Terminal Velocity - Drag Force - Important Equations and Quantities

Drag force

The actual force of air resistance is quite complicated. Experiment by moving a book through the air with the face of the book and then the side of the book forward, you will agree that the area of the book makes a difference as to how much you must work in order to move the book at the same speed in both cases. This is why racing cars are slim-lined in design, and not shaped like a big box!

Get a plastic container lid (or anything waterproof) swing it around in air and then try to swing it around under water. The density of the water is much larger than the air, making you have to work harder at swinging the lid in water. This is why boats and submarines are a lot slower than aeroplanes!

So we know that density, area and speed all play a role in the drag force.The expression we use for drag force is

{\begin{matrix}D={\frac {1}{2}}C\rho Av^{2}\end{matrix}}

(9.25)

where C is a constant which depends on the object and fluid interactions, $\rho$ is the density, A is the area and v is the velocity.