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Die Physik von Aristoteles The word “physics,” comes from the Greek word phusis. This is usually translated as “nature,” but not nature in the sense that we usually use the word. Aristotle might say that phusis is the internal activity that makes anything what it is. Our word for nature comes from Latin roots having to do with birth and growth, and these associations are present in the Greek word as well. It is in the “nature” of a human embryo to develop into a fetus, to be born, and eventually to become a mature human being. This is the internal activity that makes it what it is. One of Aristotle’s most influential books is entitled simply Phusis, or as it is always translated, Physics. Alfred. W. Stetz , Beginning with Aristotle, Life, the Universe and Everything
Aristotle Something which we have to recognize is the investigation method of Aristotle that is actually not really different than used in any scientific publication today. He defined the subject matter, discussed the ideas and work of others on the subject being critical with logical problems of their models, and finally he presented his own views and possible solutions. Before anything else, I may say that the old theories are crude and inexact. Men were still in error about the truth. Everything was new for men who were making the first attempts. Later these same theories were refined. Yet if anything has been discovered, it none the less ought to be acknowledged as having been received from them. It was the achievement of a great spirit to move aside the veil from hidden places and, not content with the exterior appearance of nature to look within and to descend into the secrets of the gods. The man who had the hope that the truth could be found made the greatest contribution to its discovery. And so the ancients must be listened to, indulgently Nothing is completed while it is beginning. This is true not only in this subject (which is the greatest and most complex of all), but in every other business as well. Even though much will have been done on the subject every age will none the less find something to do. As in every other subject, the first beginnings have always been far away from the completed knowledge! Seneca Natural Questions we know experiments were performed by ancient Greeks to increase the effectiveness of these weapons. Empirical laws have been found by these experiments that were reproduced later by Hook. We also have to consider that Aristotle obtained his results from observation of natural phenomena. He did not have experimental methods to produce a vacuum or to reduce the friction to observe the dependency on the density. Aristotle did not accept the heliocentric model because he assumed that the centripetal acceleration would cause objects on the earth to fly off at night. The effect is real we do weight less at night than at day for this reason. But the effect is small compared to the earth's gravity which keeps us on the ground.
It has, of course, been known since the days of the ancient Greeks that in order to describe the movement of a body, a second body is needed to which the movement of the first is referred. Albert Einstein, 1919 Michael Rowan Robinson a professor of astrophysics in the Blackett Laboratory, Department of Physics, Imperial College, London provides very interesting information about Aristotle's contribution and ideas in Physics: Comments by M. R. Robinson about the Physics of Aristotle: Aristotle did not analyze frictionless uniform motion because such motion is not seen in the world. It was not until Newton that this Platonic concept of uniform motion in a straight line under no force was seen to be fundamental to dynamics. Aristotle considered the motion under a constant force resisted by friction - such as a body of mass m being pulled or pushed along the ground. The corresponding Newtonian equation of motion is mdv/dt = F - µmg, where dv/dt is the acceleration, µ is the coefficient of friction, and g is the acceleration due to gravity. For uniform motion we then require, as stated by Aristotle, that a constant force (equal to µmg) must be exerted to overcome friction. The second state analyzed by Aristotle is uniform motion through a resistive medium like air or water - such as a body in free fall through a viscous medium. This was first correctly analyzed by Stokes in the 19th century, who recognized that the resistive force is proportional to the velocity. For a slowly falling sphere of radius r then (neglecting buoyancy) mdv/dt = mg - 6 pi r eta v, where eta is the coefficient of viscosity, that Aristotle called "thickness" of the medium. The terminal velocity achieved by the falling body is v = mg/6 pi eta r. Aristotle, said that the terminal velocity is inversely proportional to the cross-sectional area,, i.e. r2, rather than the radius. "The medium causes a difference [in the motion]," he wrote, "because it impedes the moving body, most markedly if it is moving in the opposite direction, but to a lesser degree even if it is at rest; and this is particularly true of a medium that is not easily cut through, i.e. a medium that is on the thick side. A body will move through a given medium in a given time, and through the same distance in a thinner medium in a shorter time, in proportion to the thicknesses of the hindering media." Aristotle came close to a correct statement of Stoke's formula for the terminal velocity in a resistive medium. His analysis of the real, frictional and viscous world is therefore superior in some respects to that of Newton. Newton's great advance was to deal with accelerated motions. Aristotle was aware that accelerations took place, but he was not able to incorporate them quantitatively. In retrospect, the Achilles' heel of Aristotle's theory was his treatment of bodies moving against slight resistance. The problem is that the Stokes-Aristotle terminal velocity becomes very large as the viscosity tends to zero (as in air) and becomes infinite in the limit of a vacuum. Aristotle responded by saying a vacuum was impossible, but this still did not obviate the need to consider accelerations properly for motion of a projectile in air. Another fundamental insight of Aristotle's that was not correctly formulated by Newton was the concept of power. Aristotle correctly defined the power of a machine lifting a body as being the weight multiplied by the distance moved, divided by time - in other words the rate of doing mechanical work. He also, very practically, pointed out that there is a threshold to get something moving when there is resistance by friction - One man cannot move a ship, as he put it. Aristotle had a reasonably clear notion of buoyancy - that a denser body sinks through a medium while a lighter one rises. He elevated this to a universal process of bodies either seeking the center of the Earth or moving away from it, depending on whether they are lighter (hot air or fire) or heavier (earth) than air or water. When he considered if the Earth itself could be moving round the Sun, he found that this idea conflicted with the seemingly more powerful notion of a natural motion towards or away from the center of the Earth. This led him to postulate that the circular motions of heavenly bodies about the Earth once a day must also be one of the possible natural states of motion. He also had to argue that the universe is finite to avoid infinite circular velocities at the periphery. This picture is another reason why he rejected the idea of uniform motion in a straight line, because it would have implied the concept of an infinite straight line, which is not permitted in a finite universe. Aristotle reduced all forces to pushes or pulls and could not conceive of gravity holding the planets in circular orbits. He did, however, see that forces act at a point and have a definite direction, i.e. that force is a vector. Aristotle thought that the stars were at a range of distances from the Earth, and believed that the stars were spheres. Thus the crude medieval picture of the stars as "holes" in the surface of a sphere that let through light from behind had absolutely nothing to do with Aristotle. Perhaps Aristotle's most enduring contribution to cosmology was his concept of a uniform ever-flowing time. This was taken over without modification by Newton. and was not questioned until the rise of relativity theory at the start of the 20th century. In the special theory of relativity, the rate at which time flows depends on the relative motion of the observer and the clock, although an inertial, uniformly moving observer would still see a uniform time pervading the universe within his or her own frame of reference. In general relativity, the patch over which a freely falling, inertial observer can measure such a uniform time becomes localized to the zone in which the gravitational field is uniform. Amazingly, though, when we apply general relativity to a homogeneous and isotropic universe - and there exist strong observational reasons for supporting such a model - Aristotle's uniform cosmic time pervading the universe reappears. Moreover, it is the same time for every observer co-moving with the universe. I find this one of the most paradoxical features of the universe we appear to find ourselves in. The goal of Aristotle's physics was to be able to comprehend all phenomena. Newton's work was different: he wanted to analyze and predict a subset of the phenomena that are amenable to equations. , Oxford University Press , 0199247900, 2005 German / Deutsch Aristoteles, Kant und die Quantenphysik ( |
