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free fall, in physics, the state of a body moving solely under the influence of gravitational forces (see gravitation). A body falling freely toward the surface of the earth undergoes an acceleration due to gravity of 32 ft/sec^{2} (9.8 m/sec^{2}), which is symbolized by *g.*

The Columbia Electronic Encyclopedia Copyright © 2004.

Licensed from Columbia University Press

Licensed from Columbia University Press

In mechanics, the state of a body that moves freely in any manner in the presence of gravity. The planets are in free fall in the gravitational field of the Sun. A body in free fall follows an orbit such that the sum of gravitational and inertial forces equals zero. *Seealso* gravitation; Newton's laws of motion.

Learn more about free fall with a free trial on Britannica.com.

Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.

Free fall is motion with no acceleration other 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 aerodynamic drag, in nontechnical usage falling through an atmosphere is also referred to as free fall.

- A spacecraft (in space) with its rockets off (e.g. in a continuous orbit, or going up for some minutes, and then down)
- The Moon orbiting around the Earth.
- An object dropped in a drop tower for 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 force from 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.

- $v(t)=-gt+v\_\{0\},$

- $y(t)=-frac\{1\}\{2\}gt^2+v\_\{0\}t+y\_0$

where

- $v\_\{0\},$ is the initial velocity (m/s).

- $v(t),$is the vertical velocity with respect to time (m/s).

- $y\_0,$ is the initial altitude (m).

- $y(t),$ is the altitude with respect to time (m).

- $t,$ is time elapsed (s).

- $g,$ is the acceleration due to gravity (9.81 m/s
^{2}near the surface of the earth).

- $ma=-kv-mg,$

where

- $m,$ is the mass of the object

- $k,$ is the friction coefficient

- $v\_\{yinfty\},$ is the terminal velocity,

- $frac\{dv\}\{dt\}=-g(1+frac\{k\}\{mg\}v)$

- $int\; frac\{1\}\{1+frac\{k\}\{mg\}v\},dv=-gint,dt+C$

- $frac\{mg\}\{k\}ln\{(1+frac\{kv\}\{mg\})\}=-gt\; +C$

- $v=frac\{mg\}\{k\}[exp(-frac\{kt\}\{m\}+frac\{kC\}\{mg\})-1]$

- $v\_\{infty\}=lim\_\{t\; to\; infty\}v\; =\; -\; frac\{m\}\{k\}g$

- $y=-frac\{m\}\{k\}\{(v\_\{o\}+frac\{m\}\{z\}g)(e^\{frac\{-k\}\{m\}t\}-1)+gt\}+y\_0.$

- $mfrac\{dv\}\{dt\}=-frac\{1\}\{2\}\; rho\; C\_D\; A\; v^2\; -\; mg,$

where

- $m,$ is the mass of the object,

- $g,$ is the gravitational acceleration,

- $C\_D,$ is the drag coefficient,

- $A,$ is the cross-sectional area of the object, perpendicular to air flow,

- $v\_y,$ is the fall (vertical) velocity,

- and $rho,$ 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

- $v(t)\; =\; -v\_\{infty\}\; tanh(frac\{gt\}\{v\_infty\}),$

where the terminal speed is given by

- $v\_\{infty\}=sqrt\{frac\{2mg\}\{rho\; C\_D\; A\}\},$.

In World War II there were several reports of military aircrew surviving long falls: Nick Alkemade, Alan Magee, and I.M.Chisov all 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 fuselage in freefall mode), but died from their injuries before help arrived.

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, Russia on November 1, 1962. Andreev did not use a drogue chute during his jump.

Captain Kittinger was then assigned to the Aerospace Medical Research Laboratories at Wright-Patterson AFB in 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.

On 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) 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.[1] He set records for highest balloon ascent, highest parachute jump, longest drogue-fall (14 min), and fastest speed by a human through the atmosphere[2].

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 cluster to his D.F.C. and awarded the Harmon Trophy by President Dwight Eisenhower.

- Details of the Excelsior I free-fall
- Details of the Excelsior II free-fall
- Details of the Excelsior III the biggest free-fall in history
- Unplanned Freefall? A slightly tongue-in-cheek look at surviving free-fall without a parachute.
- Free fall accidents, mathematics of free fall - detailed research on the topic
- parachute history

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Last updated on Saturday October 11, 2008 at 12:42:24 PDT (GMT -0700)

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This article is licensed under the GNU Free Documentation License.

Last updated on Saturday October 11, 2008 at 12:42:24 PDT (GMT -0700)

View this article at Wikipedia.org - Edit this article at Wikipedia.org - Donate to the Wikimedia Foundation

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