free fall(redirected from free-fell)
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free fall,in physics, the state of a body moving solely under the influence of gravitational forces (see gravitationgravitation,
the attractive force existing between any two particles of matter. The Law of Universal Gravitation
Since the gravitational force is experienced by all matter in the universe, from the largest galaxies down to the smallest particles, it is often called
..... Click the link for more information. ). A body falling freely toward the surface of the earth undergoes an accelerationacceleration,
change in the velocity of a body with respect to time. Since velocity is a vector quantity, involving both magnitude and direction, acceleration is also a vector. In order to produce an acceleration, a force must be applied to the body.
..... Click the link for more information. due to gravity of 32 ft/sec2 (9.8 m/sec2), which is symbolized by g.
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 vt 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 vf, attained when a body falls freely from an infinite distance to the surface of the Earth, is given by Eq. (2),
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 fallMotion of a body under the influence of gravity alone, i.e. with no other forces acting. See also weightlessness.
free fall[′frē ‚fȯl]
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.