# How Fast Do Peregrine Falcons Dive?

How fast can a peregrine falcon fly/dive? In this amazing video, one scientist aims to find out by skydiving along with a peregrine falcon. [2:59]

1. #1 Tegumai Bopsulai, FCD
January 24, 2008

Is that an African peregrine falcon or a European peregrine falcon?

2. #2 Bob O'H
January 24, 2008

It can’t have been European – it was diving in miles per hour, and we’re metric.

Bob

3. #3 Bob
January 24, 2008

I wouldn’t call that “flying”–the bird’s just in free fall. The guy taking the pictures is “flying” equally fast–would you say humans can fly 200 mph? I’m sure a lead brick dropped out of a plane can “fly” even faster.

It’s my recollection that the fastest bird in actual flight is a species of swift.

4. #4 Aaron Lemur Mintz
January 24, 2008

A lead brick can “fly” even faster, but it can’t pull out of the dive. I think that’s the big difference here.

5. #5 anon
January 24, 2008

Actually, as old Galileo pointed out, the lead brick would fall at almost the same speed, (slightly slower actually, because of more drag).

6. #6 "GrrlScientist"
January 24, 2008

the bird is in a controlled fall, since it can steer and it will not go splat as would happen in free fall.

and a lead brick will not free fall faster than a human or a peregrine — according to my physics classes, everything reaches the same terminal speed, regardless of its mass. objects can free fall more slowly due to friction, though.

7. #7 Bob O'H
January 24, 2008

Hey, what about a streamlined brick?

8. #8 Strabo
January 24, 2008

A lead brick will have a higher terminal velocity than a human of the same mass. Because it’s denser.

The force because of gravity is solely proportional to the objects mass, but the drag force cause by air resistance will be (Roughly, IIRC) proportional to the objects cross sectional area multiplied by it’s speed. The lead brick has a smaller cross sectional area, so it will have to go faster than the human before the drag force cancels out the gravitational force.

To make it more obvious, compare the terminal velocity of a bubble or a balloon to that of a brick.

9. #9 Bob
January 24, 2008

…according to my physics classes, everything reaches the same terminal speed, regardless of its mass.

You should demand a refund on your tuition. To quantify Strabo’s argument, an object reaches terminal velocity when air resistance (roughly proportional to cross sectional area) equals gravitational force (proportional to mass.) So objects with the same terminal velocity must have the same ratio of mass to area. Since mass is equal to density times volume, and area is proportional to the 2/3 power of volume, a little algebra shows that for objects with the same terminal velocity, area is proportional to the inverse square of the density. Since lead is about ten times denser than human flesh, the terminal velocity of a lead brick will be greater than that of a man as long as the brick is large enough to have more than 1% of the man’s cross section.

10. #10 Chris
January 24, 2008

It’s not that everything will reach the same terminal velocity regardless of its mass. What matters is the relationship between an objects mass and its drag coefficient. Terminal velocity occurs when the force due to gravity is balanced by the opposing component of the drag. A lead brick will fall decidedly faster than a human over a long distance, though they will accelerate at the same rate for a moment. The terminal velocity of a human, and a falcon, for that matter is variable. The diver falls slowly in a spread eagle posture and goes head down, feet up, arms in to speed up. The cool thing about the falcon is that it can basically reduce itself to a missile. Regardless of whether it’s self propelled or gravity assisted, I think its pretty awesome that it can slick itself down enough to get up to 240 while retaining enough control to hit a moving target (though admittedly the lure was an easy one, since it was going straight down at high speed-the relative velocity must have been small). The reflexes it must take to break out of that posture and grab the evading prey must be fantastic.

11. #11 rex
January 24, 2008

As Strabo says, falling objects accelerate until the drag force equals the weight (which is also a force). At low speeds the drag force is proportional to velocity, but at the speeds humans and birds fall, drag is proportional to the square of velocity.

The terminal velocity of a large (birds are ‘large’) object is given by:

Vt = sqrt(2*m*g/(p*a*Cd))

Where:
m = mass,
g = acceleration of gravity (32 ft/sec^2)
p = density of the medium (air, in this case)
a = reference area (related to, but not the same as the frontal area)
Cd = coefficient of drag

There’s a good article on this at:

http://en.wikipedia.org/wiki/Drag_(physics)

However, the estimate for terminal speed of diving birds is very inaccurate because it ignores the very low drag coefficient of a streamlined bird.

-rex

12. #12 Tegumai Bopsulai, FCD
January 24, 2008

according to my physics classes, everything reaches the same terminal speed, regardless of its mass.

Yes, but you forgot those important last 3 words: “in a vacuum.”

13. #13 Scholar
January 24, 2008

How fast do falcons drive? It depends whether they are elderly or asian falcons.

14. #14 Nomen Nescio
January 24, 2008

tetrapyloctomy warning in effect: Tegumai’s oversimplifying. in a vacuum there is no terminal velocity, except whatever velocity has been attained when the falling object(s) impact one another, if they do.

15. #15 Autoversicherung
January 25, 2008

It can’t have been European – it was diving in miles per hour, and we’re metric. Thanks for comments

16. #16 Kredit
January 25, 2008

Thanks. How fast do falcons drive? It depends whether they are elderly or asian falcons.

17. #17 anon
January 25, 2008

It all depends on the drag coefficient.

The air flowing around the falcon as it dives should be streamlined and the drag coefficient would be less than that of a rectangular brick falling.

18. #18 Chris' Wills
January 25, 2008

It can’t have been European – it was diving in miles per hour, and we’re metric. Thanks for comments
Posted by: Autoversicherung

Unless you include the UK in Europe :o)

Yes, I know the UK pretends to have gone metric (appeasing the EU bureaucrats) but we still have mph.

19. #19 Marco Ferrari
January 25, 2008

No brick will FLY while going downward, as the peregrin; thus accelerating.
Marco

20. #20 BaldApe
January 25, 2008

Obviously, the falcon increases its speed by reducing its air resistance. If there were no air resistance, it would continue to accelerate until it hit the ground.

Did anybody figure out how low its drag would have to be to get that terminal velocity?

21. #21 Kate
January 25, 2008

I can’t believe all the time you spent making stupid comments. Hope you had fun being nutso, instead of talking about the spectacular film footage we got to see.

22. #22 Vitis01
January 25, 2008

Thanks Kate, you beat me to it. While you guys are right, you are off topic. Furthermore, the amount of pleasure you clearly derive from showing how right you are is grotesque.

23. #23 Marco Ferrari
January 26, 2008

If Kate’s post was meant for me, it was misdirected. Peregrin falcon really fly downward while diving.
Marco