# Air resistance in projectile motion

Steven_Scott
In lower-division physics classes, air resistance is usually ignored to make the mathematics of projectile motion easier to understand.

When air resistance is included, it's often stated that at lower velocities, air resistance is proportional to the velocity of the object,

Fair ∝ kv

At higher speeds, air resistance becomes proportional to the square of the velocity,

Fair ∝ kv2

What I'm wanting to know is, how do we know at what speed air resistance is simply proportional to velocity and when does it become proportional to the square of the velocity?

Is there an easier way to determine when this "transition" takes place or does it depend on the geometry of the object you're working with?

Staff Emeritus