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.