Learning objectives
- Explain why air resistance grows as speed increases.
- Identify terminal velocity as zero acceleration, not zero velocity.
- Compare weight and drag throughout a fall.
- Predict how mass, area, shape, and air density affect terminal speed.
The force story
- Just after jumping, speed and drag are nearly zero, so weight accelerates the diver downward.
- As speed rises, drag rises approximately with speed squared.
- Eventually drag equals weight. Net force becomes zero.
- The diver then continues downward at constant terminal velocity.
Important: terminal velocity does not mean the diver stops. It means the speed stops changing.
Model used
Weight = mass × gravity.
Drag = one half × air density × drag coefficient × area × speed squared.
Terminal speed occurs when drag equals weight.
Try these investigations
- Compare belly-to-earth with a head-down dive.
- Open the parachute and watch drag briefly exceed weight.
- Increase mass while keeping area constant.
- Lower air density to model high altitude.
- Pause near terminal speed and compare both force arrows.