go to this website to watch the animation: http://regentsprep.org/Regents/physics/phys01/terminal/term3.htm

Terminal velocity is encountered any time you drive your car with a constant speed. The animation below shows the forces acting on a car starting from rest.

Be sure to watch the animation enough times to examine the following key concepts:
Initially, the applied force from the engine is the net force.
As the speed of the truck increases, the force of air friction (drag) also increases. The faster the car goes, the smaller the net force becomes.
Once the Fengine is cancelled out by the Fdrag, the net force is zero so there is no acceleration. The car moves with a constant velocity of 20 mph. 20 mph is the terminal velocity!