# Terminal velocity. ???

No, not that shitty Wesley Snipes movie.
Can anyone explain to me (Lex=layman) what the deal is with terminal velocity? I want to know how fast you fall before you can’t fall any faster, variables like drag and such kept to minimum, if that’s possible.
So:
How fast is terminal velocity?
Is it a constant or a variable?
How do you figure it?
Thanks in advance all you smart physics folks.

“Winners never quit and quitters never win, but those who never win and never quit are idiots.”

The air resistance you face is proportional to the cube of your velocity. The force of gravity is a constant. When your velocity causes an air resistance equal to the force of gravity, you stop accelerating and reach terminal velocity.

This phenomenon is also responsible for your car having a maximum speed. If you were driving on an airless planet, you could keep adjusting the gear ratio and accelerating forever (or at least until you reached a speed sufficient to send you into a very low orbit).

Lex, drag is what determines terminal velocity.

From Encyclopedia Britannica:

Wesley Snipes (or any other human) jumping out of a plane probably wouldn’t fall much faster than 150 mph.

Change the viscosity of the medium you’re falling thru and the terminal velocity changes. Wesley Snipes’ terminal velocity free-falling thru molasses would be much lower.

Gypsy: Tom, I don’t get you.
Tom Servo: Nobody does. I’m the wind, baby.

Wow, five minutes. Cool.
So, given what you know, what is the average terminal velocity of a person? Assuming they’re trying to fall as fast as possible?

“Winners never quit and quitters never win, but those who never win and never quit are idiots.”

Holy shit on a popsicle stick, batman!
And here I thought Alphagene hated my guts!
Thanks for all the good info, man!

“Winners never quit and quitters never win, but those who never win and never quit are idiots.”

Lex,

If I recall high school physics correctly, terminal velocity should be in the region of 132 to 138mph.

You aren’t planning anything spectacular I hope.

Kalél
Common ¢ for all ages…
“If ignorance is bliss, you must be orgasmic.”
“Well, there was that thing with the Cheese-Wiz…but I’m feeling much better now!” – John Astin, Night Court

apparently it is possible for a downhill skier (you know - the ones with the silly hats and the rubber suits) to travel faster than the terminal velocity for a human skydiver. The problem with this is that the skier is not travelling vertically but along the gradient of the slope. Just wonder how fast a skydiver would go if he wore a silly hat???

It depends on who you ask I guess.
Check out Speed of a Skydiver (Terminal Velocity)

“The terminal velocity for a skydiver was found to be in a range from 53 m/s to 76 m/s. Four out of five sources stated a value between 53 m/s and 56 m/s. Principles of Physics stated a value of 76 m/s. This value differed significantly from the others. Then again, the value is variable since the weight and the orientation of the falling body play significant roles in determining terminal velocity.”

While the human body might not be so speedy, the Peregrine falcon can attain a terminal velocity around 217mph. I would imagine some scientifically designed object could even go faster… although I do not think it would be by much.

“Wow! Spider-Man! Are you really friends with the X-men?”
"Not since Cyclops tried to use my viewmaster."
(Marvel Team Up #1)

I just like the fact that the terminal velocity of a cat is not usally terminal.

Drag is the force that the air resistance imposes on an object. That force increases with the square (not cube) of the speed. Terminal velocity is the speed at which the drag force resisting your plummet is equal to your weight pulling you down.

For those who actually want the technical definition, drag = (1/2)(density of air)(speed squared)(Surface area)(drag coefficient).

The drag coefficient is dependant on (among other things) viscosity, Reynolds number, and the shape of the object.

And wasn’t Terminal Velocity a Charlie Sheen movie? I saw it once, but it wasn’t exactly memorable.

waterj2:

Yes, I believe you are correct about T.V. being a Charlie Sheen movie.

Also, for those interested-

Just to be a tad more specific on the equation for drag, the “surface area” is not the total surface area of the object. It is the surface area of the object that is exposed to the brunt of the air resistance. So, if you were standing on the ground directly under a falling object, the surface area you would use in this equation would be the surface area of the object that you could see while looking up at the falling object (or, more simply put, the area of the silhouette of the falling object).

BTW… you may want to step to the side before the falling object lands.

Quite right, “Terminal Velocity” was a movie with Charlie Sheen and Natasha Kinski, “Drop Zone” was the Wesley Snipes, Gary Busey effort. Both had real, albeit not realistic skydiving. Among the Skydiving community it is considered that terminal velocity in the stable arch position is about 110-120mph, just how that is measured I don’t know. Tucked up in a tight cannonball position you could get up quite a bit faster. Subtle changes in position are used to effect fall rate and movement. In order to make matching fall rates easier, skinny jumpers may wear weights and heavier ones may wear a suit with a bit of fabric between the torso and under arm, both of these effect the mass to surface area ratio, which in turn determines your terminal velocity,
Larry

Sorry about not being more specific with surface area. Although frontal area is not always used. In figuring out the drag on an airplane wing for example, you generally use the area of the wing, even though it is parallel to the direction of flow.

I also remember reading that a 16 pound lead shot had a terminal velocity of around 300 mph.

Yes, it is true that there will be more resistance on a 2X2(facing the wind)X1000 object than there will be on a 2X2X2 object, but the effect of the third dimension on resistance is small compared to the two dimensions facing the “wind” directly. This equation will give a rough estimate of drag, so I was considering the third dimension of a person to have a relatively negligible effect on t.v. considering the equation is only giving an estimate anyway. It is much easier to calculate the surface area of the silhouette of a person than their actual surface area.

There’s a neat article in the current issue of Discover about the surprising way insect wings generate lift. Apparently, vortex effects have more to do with it than does frontal surface area. Skydivers aren’t exactly flat like insect wings, but a formulaic prediction based simply on frontal surface area would still tend to be faster (as in 76 m/s) than an empirical study of actual rates (like 53 m/s). Additional drag from floppy clothing (if it makes noise it’s generating drag) will also add to the frontal area drag.

BTW, the aforementioned article claims to pretty much wrap up the classic “scientists don’t know how a bumblebee can stay in the air” thing that’s been beat to death all these years.

Sure, I’m all for moderation – as long as it’s not excessive.

Yeah, it’s a Charlie Sheen movie. My bad.
Check it out here IMDB.com

“Winners never quit and quitters never win, but those who never win and never quit are idiots.”

I dont have a cite offhand for this, but a Air Force guy named Joe Kittinger(sp),back in the late 50’s or early 60’s jumped out of a balloon at about 100,000 ft. altitude. He actually broke the sound barrier, passing 700 mph.(thin air up there) He survived, and still holds the free fall record to this day, IIRC. I saw this on TLC or some such, he even had some film footage of the drop.

We had a long thread about this a while back but I can’t make the search engine do anything I want it to so you’re on your own to find it. There is some question as to whether he actually exceeded the local speed of sound but he was close enough as makes me no never mind.

“You have no choice but to be impressed.”
Tony Rothman and George Sudarshan
Doubt and Certainty