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The Geezer
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how long does it take for a sky diver to reach

Resolved Question:

how long does it take for a sky diver to reach terminal velocity. how fast would they be going. and how far would they have fallen.
Submitted: 7 years ago.
Category: General
Expert:  The Geezer replied 7 years ago.
You would think that such a typical, standard physics question would have exactly one answer. However, you can see from the website linked below that even the experts disagree:

http://hypertextbook.com/facts/JianHuang.shtml

Some excerpts from that source:

"For a skydiver with parachute closed, the terminal velocity is about 200 km/h." (56 meters/second)

"The terminal velocity of this skydiver is about 124 mph (200 kph)." (55.6 meters/second)

"The terminal velocity of a falling human being with arms and legs outstretched is about 120 miles per hour (192 km per hour)(53 meters/second) - slower than a lead balloon, but a good deal faster than a feather!"

"A person has a terminal velocity of about 200 mph when balled up and about 125 mph with arms and feet fully extended to catch the wind." (56 - 89 meters/second)

There are more entries on that site. Certainly the precise terminal velocity for a sky diver would depend on their body shape, whether or not they were in the "head down" or "spread eagle" body orientation, and other aerodynamic factors. For now, a good estimate appears to be about 120 miles per hour or 53 meters per second... close enough - BUT the qualifier is that these speeds apply in the lower levels of the atmosphere. Where the air is much thinner higher velocities are possible (see later in the cited link).

Wikipedia says this about how long it takes a sky diver to reach terminal velocity - about 15 seconds to reach 99% of terminal velocity, that is:

"...For example, the terminal velocity of a skydiver in a normal free-fall position with a closed parachute is about 195 km/h (120 mph or 54 m/s). This velocity is the asymptotic limiting value of the acceleration process, since the effective forces on the body more and more closely balance each other as it is approached. In this example, a speed of 50% of terminal velocity is reached after only about 3 seconds, while it takes 8 seconds to reach 90%, 15 seconds to reach 99% and so on..."

http://en.wikipedia.org/wiki/Terminal_velocity

Wikipedia also notes that "... the density increases with decreasing altitude, ca. 1% per 80 m (see barometric formula). Therefore, for every 160 m of falling, the "terminal" velocity decreases 1% [because the air is more dense at lower altitudes]. After reaching the local terminal velocity, while continuing the fall, speed decreases to change with the local terminal velocity..."

How far would a skydiver have fallen to reach terminal velocity? One source cites that distance as 395 meters (about 1296 feet, a quarter mile):

"...We can estimate the distance required to reach the terminal velocity to be [equation follows] 395 meters..."

http://www.pha.jhu.edu/~broholm/l10/node5.html

Now, aren't you glad you asked?
The Geezer, Successful careers
Category: General
Satisfied Customers: 1387
Experience: Retired Civil Engineer, USC Professor & Realtor, financier
The Geezer and 111 other General Specialists are ready to help you
Customer: replied 7 years ago.
by the time you got this to me i had grown tired of waiting and had found all the information on my own and judging by the what iread while scrolling to this point on the page he got the information at exactly the same sites I did. Take my money if you want . I suppose it was worth the lesson

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