The above simulation assume air drag is model with where is the magnitude of the velocity.
Nomally, for high speed projectile, the force is proportional to velocity square. i.e.
Howeve,for slow projectile, the force is proportional to velocity. i.e.
e.g. simulate a projectile moving under water.
User can adjust to find a suitable model for the case s/he want to simulated and compared with the real case under studied.
And that can be one of the purpose for the above simulation. To find out a suitbale model for a real case.