Terminal Velocity: Falling Through Drag
1 · Predict
A skydiver falls through the air, which pushes back with a drag force that grows with speed. If the skydiver adjusts their body position to increase that air drag, does their steady falling speed (terminal velocity) end up higher, lower, or the same as with less drag?
- More air drag gives a higher terminal velocity
- Terminal velocity is the same regardless of air drag
- More air drag gives a lower terminal velocity
2 · Set Up
- Open the Terminal Velocity preset. A skydiver (ball) starts near the top of the scene and falls under gravity while air drag acts on it.
- Confirm the speed probe is attached to the skydiver, then check its mass and the air drag (frictionAir) value in the Inspector panel.
- For each row below, set the skydiver's mass and air drag in the Inspector to match, run the simulation until the probe's speed reading stops changing (it will approach a steady value before the skydiver reaches the floor), and record that steady speed.
3 · Collect Data
| Mass (kg) | Air Drag | Terminal Velocity (m/s) | KE at Terminal Velocity (J) |
|---|---|---|---|
| 1 | 0.02 | ||
| 1 | 0.05 | ||
| 1 | 0.08 |
Plot air drag (x-axis) against the terminal velocity you measured (y-axis). Is the relationship a straight line? What shape is it?
4 · Analyze
- For each row, multiply the terminal velocity you measured by the air drag value, then multiply that by 60. How close is the result to 9.8 for every row? What does that tell you about the balance of forces once the skydiver stops speeding up?
- Every row uses the same mass. Does mass appear anywhere in the relationship you found in the previous question? Based on your data, does a heavier skydiver reach a different terminal velocity than a lighter one in this simulation?
5 · Extend
- Real air resistance grows with the square of speed, not directly with speed, and its strength depends on the object's cross-sectional area and mass. Predict how a real skydiver's terminal velocity would change between a belly-down 'spread eagle' position and a feet-down dive — and why mass matters for a real skydiver even though it didn't in your data above.
- A skydiver opens a parachute, which sharply increases their air drag. Using the relationship you found, predict what happens to their falling speed right after the canopy opens, and explain why they don't instantly jump to the new terminal velocity.
The Physics Behind This Experiment
Newton's Second Law at Equilibrium
Net force equals mass times acceleration. As the skydiver speeds up, the upward drag force grows until it exactly balances the downward pull of gravity — net force (and therefore acceleration) drops to zero, and speed stops changing. That steady speed is the terminal velocity you measured.
Kinetic Energy
Kinetic energy is one-half mass times speed squared. Once the skydiver reaches terminal velocity, this is the kinetic energy they carry for the remainder of the fall — energy that air resistance continuously removes as heat, keeping the speed constant.