Terminal speed: still falling, not speeding up

Two forces during a fall

Consider an object falling vertically through still air. Gravity gives it downward weight. Air resistance, also called drag, acts upward against that motion. We will ignore buoyancy in this simple model. Draw both forces before trying to explain what happens to the speed.

An unbalanced start

Our first picture shows weight of ten newtons and upward drag of six newtons. The net force is four newtons downward. Because the object is already moving down, this downward acceleration makes it speed up. The force difference matters, not just the larger arrow by itself.

The difference can shrink

As speed through the air increases, drag can increase. The upward force moves closer to the downward weight, so the net downward force gets smaller. The object can still be speeding up, just by less each second. Smaller acceleration does not automatically mean slowing down.

Balanced does not mean parked

When drag balances weight, net force is zero and acceleration is zero. The downward velocity can remain nonzero. That steady limiting speed is called terminal speed. Balanced arrows are not a parking brake. The object keeps moving unless another interaction changes its motion.

Pause at the graph

Look at the speed graph as it becomes almost horizontal. Pause and decide: is the object stopping, or is its speed changing less and less? Read the height of the curve separately from its slope. They answer different questions about the motion.

Read height and slope

The curve stays above zero, so the object is still moving. Its slope approaches zero, so acceleration approaches zero. In the smooth ideal model, the terminal value is approached rather than reached at one exact finite time. A short real fall may end well before this limit.

A surprising change of shape

Fun fact: a deployed parachute can lower the terminal speed by increasing drag. If drag temporarily exceeds weight while an object is moving down, it slows down rather than instantly stopping. Actual parachutes are specialist equipment. This is an explanation, never a suggestion to build one for a person.

Keep the conditions visible

Terminal speed depends on the object and the surrounding fluid, not just gravity alone. Shape, area, mass, and air properties matter. Continue to the worksheet to compare force arrows, interpret the graph, and distinguish constant speed from zero speed. Use diagrams and data, not dangerous drop tests.