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Q: Height required to achieve terminal velocity ( Answered,   4 Comments )
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 Subject: Height required to achieve terminal velocity Category: Science > Physics Asked by: pomakis-ga List Price: \$10.00 Posted: 13 Dec 2002 10:35 PST Expires: 12 Jan 2003 10:35 PST Question ID: 124248
 ```How high does an average limp person have to fall from to hit the ground at terminal velocity? Honestly, I'm only asking this question out of pure curiosity, and so I can point out to acrophobic friends that being on a balcony on floor x is no more life-threatening than being on a balcony at floor y. I'd like to know what the minimum value of y is for this statement to be true.```
 Subject: Re: Height required to achieve terminal velocity Answered By: tar_heel_v-ga on 13 Dec 2002 11:24 PST
 ```Pomakis.. The terminal velocity of a falling body occurs during free fall when a falling body experiences zero acceleration. The magnitude of terminal velocity depends on the weight of the falling body. For a heavy object, the terminal velocity is generally greater than a light object. This is because air resistance is proportional to the falling body's velocity squared. There is much more to determining terminal velocity than simply body posture and height. There are, however, some rough estimates that you can use in order to prove your point to your friends. It is estimated that the human body will reach 99% of terminal velocity after falling 1,880 feet (573 meters) which takes anywhere from 10-14 seconds. With normal posture and normal atmospheric pressure, this is a speed between 117 and 125 miles per hour, or approximately 54 meters per second. Another source I found stated that a human would have to fall over 400 yards (1,200 feet) prior to achieving terminal velocity. Now, a building story is approximately 12.5 feet. Using the lower number of 1,200 feet and the very basic information above, you would have to fall from approximately the 96th floor balcony to achieve terminal velocity. Now, I am sure there will be a physics genius or two that will calculate the exact distance and speed required using in depth formulas, however, I feel that the above information (and the references below) should suffice for your friends. :) Thanks for you very interesting question and I hope the above information is helpful. If you need any additional clarification, please let me know. Regards, -THV Search Strategy: terminal velocity human References: The AFU and Urban Legend Archive Death - Falling Terminal Velocity http://www.urbanlegends.com/death/falling_terminal_velocity.html Speed of a Skydiver (Terminal Velocity) http://hypertextbook.com/facts/JianHuang.shtml Ask a Scientest - Falling Bodies http://newton.dep.anl.gov/askasci/phy00/phy00012.htm Physics Forum http://www.physicsforums.com/topic.asp?TOPIC_ID=7318```
 ```There is no way anyone could fall 573 meters in 10 seconds, because even in a vacuum it would take over 10.8 seconds to fall that far. With zero air resistance, you would only fall 490 meters in 10 seconds.```
 ```Just to note - terminal velocity isn't the measure of serious harm to a falling human body. As pointed out, terminal velocity is the point at which air resistance counteracts gravity's acceleration. Falling from higher than 30 ft. is potentially fatal. At 30 ft., you'll hit the ground at approximately 22 mph. And of course, higher = faster. Even a fall from 10 ft. can cause serious injuries. From that height, you're only going to hit the ground at 8 miles an hour (a brisk jogging speed) but would you jog straight into a wall?```
 ```Without air resistance, falling from 10 ft means you hit the ground at 17 mph, and falling from 30 ft means you hit the ground at 30 mph. Air resistance at these speeds cannot account for the differences between these numbers and flajason's (especially the 10 ft value).```
 ```You are correct racecar. I neglected to use the correct formula for calculating the speed at impact. I was solving for the average velocity over the course of the fall, not the speed at impact. My apologies if I provided any misleading information. Having re-worked the math: 30 ft. = 29.67 mph 10 ft. = 17.24 mph -Flajason```