free fall

1. The fall of a body within the atmosphere without a drag-producing device such as a parachute.
2. The ideal falling motion of a body that is subject only to the earth's gravitational field.
3. Rapid uncontrolled decline: “The markets threatened to go into free fall and we came within an eyelash of … an uncontrollable panic” (Felix Rohatyn).

The accelerated motion toward the center of the Earth of a body acted on by the Earth's gravitational attraction and by no other force. If a body falls freely from rest near the surface of the Earth, it gains a velocity of approximately 9.8 m/s every second. Thus, the acceleration of gravity g equals 9.8 m/s² or 32.16 ft/s². This acceleration is independent of the mass or nature of the falling body. For short distances of free fall, the value of g may be considered constant. After t seconds the velocity v_t of a body failing from rest near the Earth is given by Eq. (1).
1.

If a falling body has an initial constant velocity in any direction, it retains that velocity if no other forces are present. If other forces are present, they may change the observed direction and rate of fall of the body, but they do not change the Earth's gravitational pull; therefore a body may still be thought of as freely “failing” even though the resultant observed motion is upward.

For a body failing a very large distance from the Earth, the acceleration of gravity can no longer be considered constant. According to Newton's law of gravitation, the force between any two bodies varies inversely with the square of the distance between them; therefore with increasing distance between any body and the Earth, the acceleration of the body toward the Earth decreases rapidly. The final velocity v_f, attained when a body falls freely from an infinite distance to the surface of the Earth, is given by Eq. (2),
2.
where R is the radius of the Earth, which gives a numerical value of 11.3 km/s or 7 mi/s. This is consequently the “escape velocity,” the initial upward velocity for a rising body to completely overcome the Earth's attraction.

Because of the independent action of the forces involved, a ball thrown horizontally or a projectile fired horizontally with velocity v will be accelerated downward at the same rate as a body falling from rest, regardless of the horizontal motion.

At a sufficiently large horizontal velocity, a projectile would fall from the horizontal only at the same rate that the surface of the Earth curves away beneath it. The projectile would thus remain at the same elevation above the Earth and in effect become an earth satellite. See also Ballistics; Gravitation.

A rapid, uncontrolled decline, as in The markets threatened to go into free fall and we came close to outright panic. This term transfers the aeronautical meaning of a free fall, that is, "a fall through the air without any impedance, such as a parachute," to other kinds of precipitous drop. [Second half of 1900s]

A parachute maneuver in which the parachute is manually activated at the discretion of the jumper, or automatically activated at a preset altitude.

See the Introduction, Abbreviations and Pronunciation for further details.

For more information on free fall, visit Britannica.com.

1. The descent of freshly mixed concrete into forms without dropchutes or other means of confinement.
2. The distance through which such descent occurs.
3. The uncontrolled fall of aggregate.

The fall of an object that has only the gravitational pull of the earth acting on it. See also acceleration of free fall.

In physics, the motion of a body being acted upon only by gravity. A satellite in orbit is in free fall, as is a skydiver (if we neglect the effects of air resistance).

(DOD) A parachute maneuver in which the parachute is manually activated at the discretion of the jumper or automatically at a preset altitude. See also airdrop; air movement; free drop; high velocity drop; low velocity drop.

Free fall is motion with no acceleration other than that provided by gravity. This also applies to objects in orbit, even though these objects are not "falling" in the usual sense of the word. Strictly speaking, nothing falling through an atmosphere can be in free fall due to the inherent resistance to motion; however, in skydiving, the term is also applied to the period of the jump before the parachute is opened, and in colloquial usage, falling through an atmosphere is normally considered to be free fall.

Examples of objects in free fall include:

• A spacecraft (in space) with its rockets off.
• The Moon orbiting around the Earth.
• An object dropped in a vacuum tube
  • 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 reaction 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.

Skydivers in the free fall portion of a parachute jump.

On Earth

Near sea level, an object in free fall in a vacuum will accelerate at approximately 9.8 m/sFailed to parse (syntax error): ^2 , regardless of its mass. With air resistance acting upon an object that has been dropped, the object will eventually reach a terminal velocity (around 120 mph (200 km/h) for a human body). Terminal velocity depends on many factors including mass, drag coefficient, and relative surface area^{[citation needed]}, 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 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 (9.8 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)

Surviving falls

JAT stewardess Vesna Vulović survived a fall of 33,000 feet (over 10,000 meters)^[1] on January 26, 1972 when she was thrown from JAT Flight 364, after the plane exploded over Srbská Kamenice in former Czechoslovakia (now Czech Republic). She broke several bones and was in a coma for 27 days.

In World War II there were several reports of aircrew surviving long falls: Nick Alkemade, Alan Magee, and I.M. Chisov all fell at least 6,000 meters and survived.

It was reported that two of the victims of the Lockerbie bombing survived for a brief period after hitting the ground, but died from their injuries before help arrived.^[2]

Record free fall

Joseph Kittinger starting his record-breaking skydive.

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.^[3]

Accidental free fall

In June 6, 1989, a NASA stratospheric balloon launched from Columbia Scientific Balloon Facility (then known as National Scientific Balloon Facility) in Palestine, Texas, suffered a uncommanded payload release while flying at 120,000 feet over a thunderstorm near Graham, in Texas. Months after the accident, a post-flight investigation concluded that a lightning bolt traveling upside from the clouds provoked the incident. The payload hit the ground at an estimated speed of 700 miles per hour. No one was harmed, but the incident forced the agency to change its policy, forbidding the flying of balloons over thunderstorms.^[4].

Free-falling aircraft and microgravity

Main article: Microgravity

External links

• 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

References

1. ^ Free Fall Research
2. ^ Cox, Matthew, and Foster, Tom. (1992) Their Darkest Day: The Tragedy of Pan Am 103, ISBN 0-8021-1382-6
3. ^ http://stratocat.com.ar/fichas-e/1960/HMN-19600816.htm
4. ^ STRATOCAT - Stratospheric balloons history and present. Full report on the uncontrolled free fall of a stratospheric balloon payload.

See also

• Free-falling aircraft

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

Dansk (Danish)
v. intr. - falde frit

Français (French)
v. intr. - descendre en chute libre

Deutsch (German)
v. - frei fallen

Ελληνική (Greek)
v. - πραγματοποιώ ελεύθερη πτώση

Italiano (Italian)
precipitare

Português (Portuguese)
v. - cair em queda-livre

Русский (Russian)
свободное падение

Español (Spanish)
v. intr. - caer libremente

Svenska (Swedish)
v. - falla fritt

中文（简体） (Chinese (Simplified))
物体未受阻碍的自由落下, 跳伞者未张伞前的下降

中文（繁體） (Chinese (Traditional))
v. intr. - 物體未受阻礙的自由落下, 跳傘者未張傘前的下降

한국어 (Korean)
v. intr. - 자유낙하 하다

日本語 (Japanese)
n. - 自由落下

עברית (Hebrew)
v. intr. - ‮צניחה חופשית‬

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