Drag and Terminal Speed from the Equation of Motion · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Falling against the wind

Science · Forces & Motion · ages 18-19
Name ______________________   Date ____________

  1. Tilting your hand edge on to the flow reduces the drag you feel.

    Circle one:   True   False

  2. Which way does the drag force point?

    • Opposite the motion
    • Along with the motion
    • Straight down always

  3. For a fast cyclist or car, how does drag grow with speed?

    • It stays the same at all speeds
    • It shrinks as speed grows
    • It grows with speed squared

  4. A skydiver opens into spread position and the facing area grows. What happens to terminal speed?

    • It drops to a lower value
    • It climbs to a higher value
    • It stays exactly the same

  5. How do you find terminal speed from the equation of motion?

    • Set the velocity itself to zero and solve
    • Set the acceleration to zero and solve
    • Delete the drag term and solve

  6. What does the speed against time curve look like for a falling diver?

    • It rises forever in a straight line
    • It rises steeply, then flattens just below terminal speed
    • It jumps straight to terminal speed at once

  7. Dust settles in still air at a slow, steady pace. Which drag rule fits it?

    • The tiny, slow rule where drag grows with speed itself
    • The fast rule where drag grows with speed squared
    • No drag rule, since dust has no weight

  8. A student draws the speed curve crossing above the terminal line and coming back. What is wrong?

    • Nothing, overshoot is normal for divers
    • The curve can never cross the terminal value from below
    • The curve should start flat and end steep
LightMySky · lightmysky.comW1-mt_In6VeoADzZ-s1

Answer key

For grown-ups. Fold this page away before handing over the rest.

Falling against the wind W1-mt_In6VeoADzZ-s1

  1. True · Less area faces the flow, so the fluid pushes back less hard.
  2. Opposite the motion · Drag always resists the motion through the fluid, so it points back against it.
  3. It grows with speed squared · At high speed through air, drag follows half C rho A v squared.
  4. It drops to a lower value · More area means drag matches weight sooner, so the steady speed is lower.
  5. Set the acceleration to zero and solve · Steady speed means no acceleration, so weight equals drag at that point.
  6. It rises steeply, then flattens just below terminal speed · Early on drag is small so speed climbs fast, then growing drag flattens the curve.
  7. The tiny, slow rule where drag grows with speed itself · Small, slow drifters live in the linear regime, so they settle quickly to a gentle terminal pace.
  8. The curve can never cross the terminal value from below · Past balance drag would beat weight and slow the fall, so crossing cannot happen.
Worksheet · LightMySky