# free fall

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## free fall

**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.*

## Free fall

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/s^{2} or 32.16 ft/s^{2}. 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).

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),

*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* Ballistics, Gravitation

## free fall

Motion of a body under the influence of gravity alone, i.e. with no other forces acting. See also weightlessness.## free fall

[′frē ‚fȯl]## free fall

**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.

## free fall

**i**. Any jump in which the parachutist pulls his own ripcord.

**ii**. The fall or drop of a body, such as a rocket, not guided, not under thrust, and not retarded by a parachute or other braking device.

**free-fall bomb**An unguided bomb that follows the rules of ballistics.

## free fall

**1.**free descent of a body in which the gravitational force is the only force acting on it

**2.**the part of a parachute descent before the parachute opens