Terminal velocity — Physical education, 14–17 years
Why a falling object can stop speeding up even though gravity is still pulling it down. Physical education, 14–17 years.
A balance while falling
As an object falls, gravity pulls it down while air resistance pushes up. At first gravity is larger, so the object accelerates. Air resistance grows with speed until it matches the weight; the resultant force becomes zero and the object continues at a steady terminal velocity.
Why falling speed has a limit
The simple phrase “gravity makes things accelerate” does not predict what happens in air for long enough. People needed to explain why raindrops, parachutists and falling objects do not keep gaining speed forever. Studying drag revealed that motion can become steady when opposing forces balance.
A parachutist’s forces
A parachutist has a weight of 700 N. Before opening the parachute, air resistance is 200 N upward, so the resultant force is 700 − 200 = 500 N downward and the speed increases. Later, resistance reaches 700 N; the resultant is 0 N, so the parachutist falls at terminal velocity.
Zero force does not mean stopped
A common mistake is to say that an object stops when the resultant force becomes zero. This is understandable because “no force” sounds like “no movement”. Zero resultant force means no acceleration: an object already moving keeps moving at constant velocity, while an object at rest stays at rest.
Parachutes and safe returns
Parachutes are designed to increase air resistance by spreading a large area through the air. The new terminal velocity is much lower, giving a person time to land safely. Engineers use the same balance of weight and drag when planning re-entry capsules and emergency escape systems.
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