What is the terminal velocity of an unladen sparrow?

If you respond with, “African or European?” you’d be corrected by my friends this morning, as I was.

“The line is actually ‘the airspeed velocity’,” they said.

Image from Wikipedia.

But out of curiosity, we decided to look it up. And to our astonishment, everywhere the internet asks about the terminal velocity of a swallow, the internet replies: Don’t you mean airspeed?

No, internet. No we do not. So we figured it out. Because this is what my friends do on a rainy Saturday morning.

Here, for your Monty Python-inspired yet strictly speaking off-script queries as to the terminal velocity of a sparrow, I bring you … The Math.

First of all. The difference between terminal velocity and airspeed velocity is (very, very basically) the difference between an object’s greatest speed at free-fall, and an object’s speed more generally while airborne. (If you want to correct me, please calm down. I am not a physicist. I’m just pointing out that it’s more than a semantic issue.)

We used this Terminal Velocity Calculator from CalcTool.org.

And we used various sources to fill in the equation:

  • Mass of a swallow = 10–60g (Wikipedia)
    We assumed it was a fairly mature swallow, and went with 50g.
  • Cross-sectional area = 3.85 cm2 (50birds.com)
    This is probably the least scientific source we used, but you try finding the cross-sectional area of a swallow without resorting to the size of a birdhouse opening)
  • Drag coefficient = 0.77 (“Field estimates of body drag coefficient on the basis of dives in passerine birds,” by A. HedenstromF. Liechti, and published in the We went with 0.77 because in our scenario, the bird is just falling, not diving.
  • Air density = 1.5kg/m3  and Gravity = 1
    These were not only the units provided in our CalcTool, but they’re also standard units for this sort of thing, my more scientific friends assure me.

Which all leads us to the conclusion that the terminal velocity of a sparrow is 105 mph.

Not this Sparrow.

That’s faster than a baseball (95 mph), slower than a peregrine falcon in all-out dive (240 mph), and slower than a human (118 mph).

Now you know.

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