Free fall

The free event is in classical mechanics the motion of a body under the sole influence of gravity. About the freefall has been speculated in antiquity. Galileo Galilei (1564-1641) explored the free fall (as well as the pendulum motion and many others) and led the inclined plane as a test set. His realization that the movement is independent of material and size of the body in free fall, rose to the principle of equivalence of inertial and gravitational mass.

Albert Einstein took for his general theory of relativity, the natural reference system is one in which the free-falling body is at rest. After the free fall completely force-free ( weightless ) and the gravitational force is an apparent force ( strong equivalence principle). His prediction that even light "falls" - it spreads in the falling reference system straight out -, was confirmed.

The approximate free fall is an introductory experiment in physics teaching. Until the air resistance becomes noticeable, it is a uniformly accelerated motion, neglecting the buoyancy, the gravitational acceleration g states is usually used. In the case of air resistance, the acceleration is not constant, however, the rate is approaching a limit speed.

Deviations from the free case are the subject of exterior ballistics.

History

The Greek philosopher Aristotle occupied himself in the 4th century BC, with the motion of bodies. In his opinion, were moving in the water heavy body down, light because of " their lightness " to the top ( ' hard ' here means: greater specific gravity than water). Heavy body would therefore fall to the ground faster than less severe.

Aristotle was the (wrong ) opinion, a body is moving during the fall at a constant speed. These views have not been seriously considered by the scholars of late antiquity, the Arab scholars and scholasticism in doubt.

However, as early as 55 BC, described the Roman poet and philosopher Lucretius in his work " De Rerum Natura " ( " On the Nature of Things" ) slower that falling objects are braked only by water or air resistance, and therefore light body, in a vacuum but must all bodies fall equally fast:

Galileo Galilei in 1590 recognized the law of free fall: all bodies fall in a vacuum regardless of their shape, composition and mass at the same speed. Your falling speed is proportional to the gravitational time, the falling distance proportional to the square of the drop time. The acceleration is in the same place for all bodies of equal size. Galilei tried to determine through experiments the gravitational acceleration. He had therefore not yet accurate timepieces and " slowed " the movements by letting roll called a chute down a ball. As a timepiece was a bucket full of water. A small jet of water poured into a beaker, and the amount of water during the fall time was weighed on an accurate scale. That he freefall also be examined, that he had two objects fall from the Tower of Pisa, is a legend.

1659-59 years after Galileo's sentence - Robert Boyle confirmed experimentally that bodies of different mass in a vacuum fall equally fast.

Isaac Newton (1642 - 1726) formulated then - in the Philosophiae Naturalis Principia Mathematica, published in 1687 - the law of gravity, which not only explains the free fall on earth, but also the orbits of the moon and planets describes as case phenomena. However, Newton's theory has no explanation for the fact that all bodies fall completely equal regardless of their material and other attributes. This was understandable only in the context of general relativity.

Free fall in the homogeneous field

Neglecting buoyancy, air resistance, increase the gravitational force when approaching the Earth and the consequences of the Earth's rotation ( Coriolis force ) an initially in- rest body falls vertically with constant acceleration g, the value of which in Germany is about (see the normal gravity formula ). The sign of g and the velocity v are positive for a downward-pointing coordinate axis s If one chooses the zero points sent ( starting at time t = 0 at s = 0), then the formulas are simple:

Hence the fall time and the terminal velocity for a given drop height to give:

A jump from the 5 - m- board therefore takes about a second and achieves a speed of about 10 m / s is equal to 36 km / h

In one case, tower case times will be up for about ten seconds duration achieved.