Free fall is motion with no
accelerationother than that provided by gravity. Since this definition does not specify velocity, it also applies to objects initially moving upward. Although the definition specifically excludes all other forces such as aerodynamicdrag, in nontechnical usage falling through an atmosphereis also referred to as free fall.
Examples of objects in free fall include:
spacecraft(in space) with its rockets off (e.g. in a continuous orbit, or going up for some minutes, and then down)
Moonorbiting around the Earth.
* An object dropped in a
drop towerfor a physics demonstration at NASA's Zero-G Research Facility Examples of objects not in free fall:
* Standing on the ground: the gravitational acceleration is counteracted by the
normal forcefrom the ground.
* Flying horizontally in an airplane: the wings' lift is also providing an acceleration.
* Jumping from an airplane: there is a resistance force provided by the atmosphere.
Near sea level, an object in free fall in a vacuum will accelerate at approximately 9.81 m/s, regardless of its mass. With air resistance acting upon an object that has been dropped, the object will eventually reach a
terminal velocity, around 56 m/s (200 km/h or 120 mph) for a human body. Terminal velocity depends on many factors including mass, drag coefficient, and relative surface areaFact|date=August 2007, and will only be achieved if the fall is from sufficient altitude.
Free fall in Newtonian mechanics
Without air resistance
where: is the initial velocity (m/s).:is the vertical velocity with respect to time (m/s).: is the initial altitude (m).: is the altitude with respect to time (m).: is time elapsed (s).: is the acceleration due to gravity (9.81 m/s2 near the surface of the earth).
= With Stokes friction =
where: is the mass of the object: is the friction coefficient: is the terminal velocity,please note that the positive direction in the coordinate system is upwards (just as in the picture to the right)
With turbulent drag
where: is the mass of the object,: is the gravitational acceleration,: is the drag coefficient,: is the cross-sectional area of the object, perpendicular to air flow,: is the fall (vertical) velocity,: and is the air density.
This case, which applies to skydivers, parachutists, or any bodies with Reynolds number well above the critical Reynolds number, has a solution:
terminal speedis given by:.
Vesna Vulovićsurvived a fall of 33,000 feet (over 10,000 meters) [ [http://www.greenharbor.com/fffolder/wreckage.html Free Fall Research] ] on January 26, 1972 when she was thrown from JAT Flight 364. The plane was brought down by explosives planted by Croatian ( Ustashe) terrorists, over Srbská Kamenicein the former Czechoslovakia(now Czech Republic). The Serbian stewardess suffered a broken skull, three broken vertebrae, one crushed completely, and was in a coma for 27 days. In an interview she commented that, according to the man who found her, "...I was in the middle part of the plane. I was found with my head down and my colleague on top of me. One part of my body with my leg was in the plane and my head was out of the plane. A catering trolley was pinned against my spine and kept me in the plane. The man who found me, says I was very lucky. He was with Hitler's troops as a medic during the War. He was German. He knew how to treat me at the site of the accident." [cite web |title=Vesna Vulovic: how to survive a bombing at 33,000 feet |url=http://www.avsec.com/interviews/vesna-vulovic.htm |author=Interviewed byPhilip Baum, Green Light Aviation Security Training & Consultancy, in Belgrade, December 2001]
In World War II there were several reports of
military aircrewsurviving long falls: Nick Alkemade, Alan Magee, and I.M.Chisovall fell at least 5,500 meters and survived.
Freefall is not to be confused with individuals who survive instances of various degrees of
controlled flight into terrain. Such impact forces affecting these instances of survival, differ from the forces which are characterized by free fall.
It was reported that two of the victims of the Lockerbie bombing survived for a brief period after hitting the ground (with the forward nose section
fuselagein freefall mode), but died from their injuries before help arrived. [Cox, Matthew, and Foster, Tom. (1992) "Their Darkest Day: The Tragedy of Pan Am 103", ISBN 0-8021-1382-6]
Record free fall
According to the
Guinness book of records, Eugene Andreev (USSR) holds the official FAI record for the longest free-fall parachute jump after falling for 80,380 ft (24,500 m) from an altitude of 83,523 ft (25,457 m) near the city of Saratov, Russiaon November 1, 1962. Andreev did not use a drogue chuteduring his jump. [ [http://stratocat.com.ar/fichas-e/1960/HMN-19600816.htm Data of the stratospheric balloon launched on 8/16/1960 For EXCELSIOR III] ]
Captain Kittinger was then assigned to the Aerospace Medical Research Laboratories at
Wright-Patterson AFBin Dayton, Ohio. For Project Excelsior(meaning "ever upward", a name given to the project by Colonel John Stapp), as part of research into high altitude bailout, he made a series of three parachute jumps wearing a pressurized suit, from a helium balloon with an open gondola.
The first, from 76,400 feet (23,287 m) in November, 1959 was a near tragedy when an equipment malfunction caused him to lose consciousness, but the automatic parachute saved him (he went into a flat spin at a rotational velocity of 120 rpm; the g-force at his extremities was calculated to be over 22 times that of gravity, setting another record). Three weeks later he jumped again from 74,700 feet (22,769 m). For that return jump Kittinger was awarded the Leo Stevens parachute medal.
August 16, 1960 he made the final jump from the Excelsior III at 102,800 feet (31 333.44 meters). Towing a small drogue chute for stabilization, he fell for 14 minutes and 36 seconds reaching a maximum speed of 614 mph (988 km/h) [http://hypertextbook.com/facts/JianHuang.shtml] before opening his parachute at 14,000 feet. Pressurization for his right glove malfunctioned during the ascent, and his right hand swelled to twice its normal size.  He set records for highest balloon ascent, highest parachute jump, longest drogue-fall (14 min), and fastest speed by a human through the atmosphere  .
The jumps were made in a "rocking-chair" position, descending on his back, rather than the usual arch familiar to skydivers, because he was wearing a 60-lb "kit" on his behind and his pressure suit naturally formed that shape when inflated, a shape appropriate for sitting in an airplane cockpit.
For the series of jumps, Kittinger was decorated with an
oak leaf clusterto his D.F.C. and awarded the Harmon Trophyby President Dwight Eisenhower.
Free-falling aircraft and microgravity
* Free-falling aircraft
* [http://stratocat.com.ar/fichas-e/1959/HMN-19591116.htm Details of the Excelsior I free-fall ]
* [http://stratocat.com.ar/fichas-e/1959/HMN-19591211.htm Details of the Excelsior II free-fall ]
* [http://stratocat.com.ar/fichas-e/1960/HMN-19600816.htm Details of the Excelsior III the biggest free-fall in history ]
* [http://www.greenharbor.com/fffolder/carkeet.html Unplanned Freefall?] A slightly tongue-in-cheek look at surviving free-fall without a parachute.
* [http://www.greenharbor.com/fffolder/ffresearch.html Free fall accidents, mathematics of free fall - detailed research on the topic]
* [http://www.parachutehistory.com/other/bonusday.html parachute history]
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free-fall — /free fawl /, v., free fell, free fallen, free falling, adj., n. v.i. 1. (of parachutists) to descend initially, as for a designated interval, in a free fall: The jumpers were required to free fall for eight seconds. adj. 2. denoting or… … Useful english dictionary
free-fall — /free fawl /, v., free fell, free fallen, free falling, adj., n. v.i. 1. (of parachutists) to descend initially, as for a designated interval, in a free fall: The jumpers were required to free fall for eight seconds. adj. 2. denoting or… … Universalium
free fall — ˈfree fall also free fall noun [singular, uncountable] JOURNALISM FINANCE when prices on a financial market go down suddenly or the economy gets worse very quickly: • After closing at $19.125 per share on Tuesday, the shares went into a free fall … Financial and business terms
free fall — n [singular, U] 1.) the movement of someone or something through the air without engine power, for example before a ↑parachute opens after someone has jumped out of a plane in/into free fall ▪ The spacecraft is now in free fall towards the Earth … Dictionary of contemporary English
free fall — free falls also free fall 1) N VAR: oft into/in N If the value or price of something goes into free fall, it starts to fall uncontrollably. [JOURNALISM] Sterling went into free fall... The price did a free fall. 2) N UNCOUNT In parachuting, free… … English dictionary
free-fall — [frē′fôl′] n. FREE FALL (sense 2) vi. free fell [frē′fel′] free fallen [fē′fôl′ən] free falling to undergo, experience, or move in a free fall … English World dictionary
free fall — ► NOUN 1) downward movement under the force of gravity. 2) rapid descent or decline without means of stopping. ► VERB (free fall) ▪ move under the force of gravity; fall rapidly … English terms dictionary
Free Fall — ist der Originaltitel des Films Angst über den Wolken die Kurzform von Free Fall Tower Diese Seite ist eine Begriffsklärung zur Unterscheidung mehrerer mit demselben Wort bezeichneter Begriffe … Deutsch Wikipedia
Free Fall — Album par Jimmy Giuffre Sortie 1962 Durée 56:57 Genre jazz Label Columbia Records Critique All … Wikipédia en Français
free fall — free ,fall noun uncount 1. ) an occasion when a price or value suddenly becomes much lower 2. ) the part of a PARACHUTE jump when someone falls quickly toward the ground before the PARACHUTE opens ╾ free ,fall verb intransitive … Usage of the words and phrases in modern English