Why doesn't the object slow down more after attaining the terminal velocity in liquid? When an object falls down in a liquid it has two forces working on it one gravity  and another is viscous drag . Now when these forces are same the object attains the terminal velocity in liquid.  Now if these forces have been neutralized then why shouldn't the viscous drag (which is proportional to instantaneous velocity of the ball so it isn't zero even after attaining the terminal velocity ) slow the ball down or accelerate it another way or upwards?
 A: Because gravity is still acting on the object. When the body is moving at terminal velocity, it's not experiencing no forces. It's just not accelerating because the vector sum of all forces on it is zero.
In the case of this object, we can say that $F_{gravity}=mg$, and since $F_{total}=0$, we must have $F_{viscous}=F_{down}=mg$. Now the total force on the object is zero, so it doesn't accelerate (or decelerate) anymore.
A: When an object has achieved terminal velocity, it experiences no acceleration.  From this, we can deduce that $F_{net}=0$.
Well, what is $F_{net}$?  It is the net force on a object; after all forces have cancelled out, what we are left with is $F_{net}$.
In our case, $F_{net}=F_{drag}-F_{weight}=0$.
A: there is more of a theoretical explanation available for this question than a mathematical one. 
forces do not have an impact on the velocity of an object, rather they have the impact on rate of change of velocity of an object(acceleration). establishing this, we can say that velocity is more about the nature of that object in our universe. this can be very well understood by considering newton's first law of motion. 
"If an object experiences no external forces, it will either stay in rest provided it was already not moving, else it will move with a constant velocity provided it was moving before."
hope it was helpful
