Terminal Velocity

In the formula v = √(2mg/(ρ·C_d·A)), mass sits under the square root in the numerator, so a heavier object needs a higher speed before drag (which depends on velocity squared, not mass) grows large enough to balance its greater weight. This is why a bowling ball and a feather with similar shapes reach very different terminal velocities — the feather's low mass lets drag catch up to gravity at a much lower speed.

Quite a lot, since C_d sits inside a square root in the denominator — going from a spread-eagle position (C_d around 1.0–1.3) to a head-down dive (roughly 0.4–0.7) roughly halves the drag coefficient, which increases terminal velocity by about the square root of that ratio, close to 40–50% faster. That's the physical basis for how skydivers control their fall speed just by changing posture, without changing their weight or gear at all.

The calculator takes air density (ρ) as a fixed input rather than deriving it from altitude, so it computes one terminal velocity for whatever density value you supply. In reality, air density drops with altitude, which by the same formula raises the true terminal velocity at that height — you'd need to enter a lower air-density value yourself to model a fall starting high up, since the calculator doesn't do that lookup automatically.

Not accurately — it uses the quadratic drag equation, which applies to objects falling fast enough relative to air that drag scales with velocity squared, appropriate for skydivers, vehicles, and similarly sized falling bodies. Very small or slow-moving objects fall in the linear (Stokes) drag regime instead, where drag scales with velocity directly rather than its square, and this formula would give a misleading terminal velocity for that case.