A skydiver steps out of a plane. For the first seconds, every second is faster than the last. Then the speeding up stops. She is still falling, and falling fast, but no faster than a moment ago.
Why would a falling object stop speeding up?
Two forces write this story: her weight, and drag from the air. You met drag as the force a fluid exerts against a mover, growing stronger at higher speed. That growth decides the ending.
At the moment she leaves the plane she falls slowly, so the drag on her is small. Her weight is far larger than the drag.
The net force on her points downward, so she speeds up.
Falling faster brings more drag: the air exerts a larger upward force on her. Her weight does not change as she speeds up. Only the drag grows.
So the downward net force shrinks as she falls faster, and she gains speed more slowly.
Eventually the drag has grown until it equals her weight. The net force on her is zero: she is in equilibrium.
From that moment she stops speeding up. She keeps falling at a constant velocity, because an object with zero net force keeps the velocity it has.
A hailstone falls and stops speeding up partway down. Why?
An acorn has just dropped from a branch and is still speeding up. Which force on it is larger?
That constant falling velocity is called terminal velocity.
Terminal velocity is not a stop. She still falls fast; what has leveled off is her speed, not her height.
A raindrop reaches a constant velocity long before it reaches the ground. Explain why, naming the two forces.
The drop's weight acts downward and does not change as it falls.
Drag from the air acts upward on the drop and grows as the drop falls faster.
When the drag has grown until it equals the drop's weight, the net force on the drop is zero.
With zero net force the drop keeps its velocity: it falls the rest of the way at its terminal velocity.
The drop stops speeding up when the growing drag balances its weight, and it falls on at a constant terminal velocity.
A falling object has reached terminal velocity. Which statement is correct?
A baseball dropped from a very tall building stops speeding up before it lands. Why?
Which ordering describes a skydiver's fall, from the jump until terminal velocity?
The constant velocity a falling object settles at, once the growing drag balances its weight, is called its ___ ___. Type the two-word name.