Question

what is the difference between constant velocity and constant acceleration in free fall?

Answer 1

In the absence of any drag forces, an object will experience constant acceleration and therefore linearly increasing velocity.

In the presence of drag forces (air resistance), when the drag force becomes equal to the force due to gravity, the object reaches an equilibrium and does not continue to accelerate. With zero acceleration, the velocity becomes constant. This constant velocity reached is called terminal velocity.

In the link below, you see a skydiver falling from an altitude of almost 39 km. Initially, at that altitude, there is a very low density of atmosphere, and thus no air resistance or drag. Thus, he falls initially in with constant acceleration. His velocity exceeds the speed of sound (Mach 1) at around 33 seconds into his fall. As he continues to drop, the density of air increases to the point where his velocity begins to decrease. Eventually, his velocity approaches a terminal velocity as his altitude drops below 4 km.

If you plot his velocity vs. the clock time in the video below, you can see that initially, his velocity is increasing linearly.

Link --> https://goo.gl/4QXYpK

-- Bill

Answer 2

Velocity is the rate of change of displacement.
Acceleration is the rate of change of velocity.
Constant velocity means the rate of change of displacement is constant.That means no acceleration. Because of you have an acceleration then the rate of change in velocity differs thus the making a difference in rate of change of displacement. Throughout the motion the velocity doesn't change.

Constant acceleration means the rate of change of velocity is constant. ( that means the velocity is changed by a same factor )
Ex: Think of car which has an initial velocity 2ms^-1 and a constant acceleration of 1ms^-2
Time 0 1 2 3 4 5
Velocity 2 3 4 5 6 7

In each second the velocity is increases by one unit.