If I threw an object straight down from a high-enough distance would the object begin to decelerate until it reached its terminal velocity or would it continue downward at a rate faster than terminal velocity?
I believe that you’re correct. If you threw the object at a rate faster than its terminal velocity, it would slow down to T.V.
Assuming you’re in the atmosphere. Collision with the atmosphere slows things to terminal velocity. If you are large enough or fast enough, there isn’t enough atmosphere to slow you to terminal velocity before you hit the ground…
Given a hypothetical infinitely tall tower, and a hypothetically even atmospheric pressure for the height of the tower, then the downward impetus will contribute nothing but the initial velocity of the object.
The object will immediately be acted on by wind resistance, and gravity; the high velocity means that wind resistance will be larger than gravity, and therefore the object will decelerate until these forces are equal - i.e. R = g.
Think if it another way: imagine throwing a flat piece of tissue paper downwards from a tall building. No matter how hard you threw the tissue paper, it would decelerate dramatically, within fractions of a second, to its slow, fluttery terminal velocity.
One way to think about this problem is as an elementary force balance. The object is pulled toward the Earth with a force of mg (mass times acceleration due to gravity). This force is opposed by a drag force, C[sub]D[/sub]A[symbol]r[/symbol]V[sup]2[/sup]/2, where C[sub]D[/sub] is the coefficient of drag, A is the frontal area, [symbol]r[/symbol] is the air density, and V is velocity. Note that the drag force increases with increasing velocity (and the gravitational force is constant).
If the gravitational force is greater than the drag force, the unbalanced force speeds the object up. If the drag force is greater than the gravitational force, the unbalanced force slows the object down. Either way (unless the ground intervenes), eventually the drag force is adjusted until it is equal to the gravitational force. At this point, all forces are in equilibrium, and the object reaches a constant speed: the terminal velocity.