Terminal velocity means zero acceleration, not zero forces
The mistake
Assuming a falling object at terminal speed has no forces acting.
Why it feels right
No acceleration sounds like nothing is happening dynamically.
How to catch it
You erase gravity when drag balances it.
The first principle
At terminal velocity, net force is zero because drag equals weight. Gravity and drag still act; they balance.
worked mini-example
A skydiver falls at terminal speed. What is the net force?
Common wrong move
mg downward because the skydiver is still falling.
Correct
Zero net force; drag upward equals mg downward.
Test the repair NL-16 · transfer
Make a fresh prediction before referring to the worked example.