History.of.dynamics.and.the.most .important.scientistsAn analysis of the movement must begin with the ancient Greeks. Since the effect of the Greeks lasted two millennia, it is unthinkable to describe the growth of the dynamics without taking this into account. The dominant figure in the ancient evolution of dynamics was Aristotle (384 BC – 322 BC). His writings (Aristotle, 330 BC) on this and many other topics have influenced much of science for the next two thousand years. Much of his reasoning on the movement came from the wrong conception of the classical elements (fire, air, water and earth). Each of these has its natural place in the world: the fire at the top; infra of aerial fire; water under the air; and finally the earth rests under all of them. Every time an element was taken from its natural place, it tried to return. This reasoning explains why an air bubble breathes underwater floats on the surface, and why a rock thrown upwards falls back to Earth. Each object was therefore a combination of all these. A feather, lighter than a rock, must have more air than the rock, but less than the air itself. From this line of thought comes the “natural movement”: movement that occurs because of the nature of the object. The rest of the movement was violent; I had a separate cause. A brick that falls to the ground would be natural, but a trap launched from the air would be violent. Aristotle concluded that heavier objects fall faster than light objects and that this fall rate is proportional to their weights: an object the heaviest double falls twice as fast. He also thought that the speed of progression through a medium was inversely proportional to the density of that medium. This intellect implied that the speed of progression in nothingness would be infinite; therefore, he came to the conclusion that the very existence of nothingness was impossible (Aristotle (330 BC), Book IV: 8). they are finished), but there is no empty relationship. In the same section, he wrote that if there were a gap, heavy objects fall at the same rate as light ones (“So, everyone will have the same speed, but this is impossible”). He used this alleged fall rate equality and then said for modus tollens that emptiness can not exist. Furthermore, he wrote that, in the void, there would be no reason for a body to stay in one place or move to another and, therefore, the movement will continue forever. It is often said, on the basis of this statement, that he has enunciated or predicted a principle of inertia, but this is only possible through a selective reading of his works. Among the various physical questions posed by the ancient philosophers, the question of why an arrow continues to fly after leaving the rope has been particularly disconcerting. Aristotle thought that the arrow had moved the air in front of him, that he rushed backwards and pushed the arrow forward. The idea of something that moves violently without another thing pushing it in between; moving without an engine was completely foreign to the Aristotelians. This deceptive division of the natural and violent movement will persecute physics for another two thousand years. Progress towards a real proxy was slow and stopping the world view of Aristotle was rooted in science and in Western and Arab deities. Its dominance in the last of these fields has influenced the progression of the latter. Much of this has become the Church’s creed. Raising his theology above and above the toast, he raised a wall of protection, with power, around his physics. The prolonged rule of Aristotle is now difficult to imagine. No, in the early contributions of the Renaissance to the physics of the philosophers it would be based exclusively on the comments to the works of Aristotle: two millennia after their composition. The sixth-century Alexandrian philosopher, John Philoponus (c. 490-ca. 570), wrote great objections of Aristotelian physics (Philoponus, 2006), and this is where one can see the shadow of a modern and dynamic. Philoponus has found little satisfactions in Aristotle’s attitude, in fact he has also found few satisfactions in his other focal points. In his comments he demolished the work of Aristotle on the natural and violent movement.For the natural movement, Philoponus states that an object has a natural fall rate. Falling through a medium would prevent this natural speed: but a strange time is necessary because of the medium’s intervention. It showed a natural shock rate in the vacuum and the effect of the average resistance decreased. This concept allowed him to deny the Aristotelian concept that the speed with which objects fall are linked to their weights. He did so by appealing to the same kind of experiment conducted in Renaissance Italy about a millennium later. Filopono did not believe in equal rates of fall into the void. In fact, he came to the conclusion that this concept was wrong. His belief was that heavier objects fell faster than light objects in a vacuum. By violent movement, said that when an object moves, a limited supply of force force is given5: a supply of force, while it lasted, explain the continuous movement of the object: rather it is necessary to assume that some reason en` disembodied Ergeia is imparted by the projector to the projectile … This erroneous reason in energeia is exhausted in the course of the movement of an object, which rests when this exhaustion is complete. This property was internal to the body. He came very close to a kind of rudimentary concept of kinetic energy. At least, he approached some concepts that we can now relate to kinetic energy. The conclusion of the sentence quoted above is: … and that the air set in motion does not contribute to anything or very little to this projectile movement. The strongest and most innovative idea made by Philoponus was that a medium did not play a role in maintaining movement. It acts like a delayed force. This notion was in direct opposition to Aristotle, who demanded that the medium cause a continuous movement. This change of paradigm introduced by John Philoponus allowed him to explain that movement in the void was possible. Your lasting contribution is with these qualitative analyzes. Their quantitative explanations lack merit, even if these analyzes resonate through the dynamics of Galileo. In the centuries that followed Filopono, other philosophers followed a surprising and dangerous progression to Newton. Another millennium would have passed before the Aristotelian movement was discarded. The reasons are different, but a large part of they are theological in nature. Filopono’s writings in tritism were declared anathemas by the Church, which led to the negligence, condemnation and ridicule of his writings. Zimmerman said the following (Zimmerman, 1987): his writings, then and later, enjoyed notoriety rather than authority. The inferior works of the mechanics of his contemporaries, such as Simplicio, were treated in a more favorable way.The Middle Ages In the following centuries, the development of dynamics was very slight. There is a pernicious popular belief that science stood still from the fall of the Western Roman Empire (476 A.D.) until the Renaissance: the so called Dark Ages. While the remark may hold water for certain periods of the Early Middle Ages, it has no standing whatsoever with the High and Late Middle Ages. The idea that the world of understanding stood still for a millennium is a hopelessly incorrect one. Aristotle’s views, or variations on these, were analysed further by the likes of the Andalusian–Arabs Avempace and Averr¨oes6 in the mid–13th century. The gratitude owed to these philosophers should not be understated. It is through their works that Philoponus’ thoughts were preserved: his books were not published in Western Europe until the early 16th century. Averr¨oes wrote such extensive treatises on Aristotelian physics and theology that he was nicknamed The Commentator by Thomas Aquinas. The intellectual stupor existed in the West because an Aristotelian theological worldview was dogma. Those studying mechanics were reticent to go further than simple reinterpretation of Aristotle, even when so much of it was clearly wrong. The stimulus that reinvigorated the field can be traced to the Condemnations of 1277. In this year, Tempier, the Bishop of Paris, condemned various doctrines enveloping much of radical Aristoelianism and Averr¨oeism, among others. This event is important because the condemnation of Aristotle’s theology led philosophers to question the truth of the rest of his worldview. Deviating from dogma was then, and remained for centuries more, very dangerous for philosophers, but now Aristotle’s physics were no longer protected. The importance of the Condemnations led to what Duhem (1917) called: …a large movement that liberated Christian thought from the shackles of Peripatetic and Neoplatonic philosophy and produced what the Renaissance archaically called the science of the ‘Moderns.’ Soon after, in the early 14th century, the Oxford Calculators7 explained, in a kinematic sense, the motion of objects under uniform acceleration. Importantly, these men did not concentrate solely on the qualitative description of motion. What was previously a murky description of motion became a quantitative derivation. They answered kinematic questions numerically. What is fantastic is that the notion of instantaneous speed was within their grasp, even without the strong grip afforded us by calculus. The mean–speed theorem dates from this period, and is attributed to William Heytesbury8 . That theorem sprung from the investigations into how two bodies moving along a path at different speeds might arrive at an endpoint at the same time (see the essay “Laws of Motion in Medieval Physics” in Moody (1975)). They were additionally responsible for separating motion itself from its causes: the separation of kinematics and kinetics. Bradwardine9 also noted: All mixed bodies10 of similar composition will move at equal speeds in a vacuum. The statement above shows that the Mertonians were well aware of the principle that objects of the same composition fall at the same rate, regardless of their mass. The fall rates were still explained in terms of the nonsense classical elements of Ancient Greece, but they were explained. Within their work can be found thorough analyses of uniform and accelerated motion. Their analytical approaches to motion were well received Europe–wide. French priest Jean Buridan (1300–1358) was by most accounts the giant of fourteenth century philosopy. He expounded a theory that can properly be described as an early and rudimentary concept of what we now call inertia. He posited in a similar manner to Philoponus that the motion of an object was internal to it, and importantly recognised that this impetus does not dissipate through its own motion: that something else must act upon the object to slow its motion. His insights into the implications of this were more advanced than anything prior. In discussing a thrown projectile, he said that it would: …continue to be moved as long as the impetus remained stronger than the resistance, and would be of infinite duration were it not diminished and corrupted by a contrary force resisting it or by something inclining it to a contrary motion. His statement is an early and rudimentary notion that is qualitatively similar to Newton’s First Law. He entertained this notion of infinite motion, a full three centuries before. His talent in descriptions of the qualitative properties was not matched by his talent in the quantitative. Buridan’s student, Nicolo Oresm`e (ca. 1323–1382), developed geometrical descriptions of motion. More than that, he used geometry as a method of explaining the variations of any physical quantity. As great as this was, he had a poorer understanding of dynamics than his tutor, and treated impetus as something which decays with motion (Wallace, 1981). Oresm`e’s work is a prime example of the stumbling advancement of dynamics: it was rare that any one person could advance in all areas at once. Albert of Saxony (ca. 1316–1390), another student of Buridan, took impetus theory forwards in projectile motion. For an object propelled horizontally, he reasoned that the motion had three distinct periods. The first of these was purely horizontal, where the body moved by its own impetus. The second was a curve towards the ground, as gravity began to take effect. The third was a vertical drop, as gravity took over and impetus died. Although maintaining the distinction between natural and violent motion, Albert at least came closer to the true shape of projectile motion. It is quite difficult to conceive the true effect that the philosophers from the Oxford and Parisian schools had on mechanics, and on science in general. Mechanics had moved from indistinct qualities into defined quantities: if an object moves at this speed, how far does it go in this amount of time? If an object accelerates in this manner, what will its speed be after a given period? These questions were asked and answered. Shortly after Giovannia di Casal`e (d. ca. 1375) returned to Genoa from studying at Oxbridge, he developed a geometric approach in his book “On the velocity of the motion of alteration” similar to that of Oresm`e. This work influenced the Venetian, Giambattista Benedetti, in his 1553 demonstration of the equality of fall–rates. The influence that Casali’s geometric approach wielded is evident while reading Galileo’s works on kinematics. An important point is then evident: the field of kinematics had leapt ahead of dynamics. Truesdell (1968) speaks of the impact of the Calculators in the following glowing terms: In principle, the qualities of Greek physics were replaced, at least for motions, by the numerical quantities that have ruled Western science ever since. While kinematics was becoming more and more capable of describing both uniform and accelerated motion, and was able to quantify these analytically, numerically and geometrically, philosophers remained unable to explain the why behind them. The causes of motion, now separate and distinct from kinematics, were not very much closer to being discovered. This situation changed very little until the late 16th century.Newton’s LawFirst lawFriction and air resistance cause a car to come to rest when the engine is switched off.If these forces were absent we belive that a body,once set in motion,would go on moving forever with a constant speed in a straight lie. That is ,force is needed to keep a body moving with uniform velocity provided that no opposing forces act on it.This idea was proposed by Galileo and is summed up in Newton’s first law of motion:A body stays at rest ,or moving it continues to move with uniformly velocity ,unless an external force makes it behave differently.It seems that the questionwe should ask about a moving body is not “what keeps it moving” but “what changes or stops its motion”. The smaller the external forces opposing a moving body, the smaller is the force needed to keep it moving with uniform velocity.An ‘airboard’,which is supported by a cushion of air , can skim across the ground with little frictional opposition, so that relatively little powe is needed to maintain motion.• Newton’s first law is another way of saying that all matter has a built-in opposition to being moved if it is at rest or, if it is moving,to having its motion changed. This property off matter is called inertia.Its effect is evident on the occupants of a car that stops suddenly; they lurch forwards an an attempt to continue moving,and this is why seat belts are needed . The reluctance of a atationary object to move can be shown by placinga large coin on a piece of cardon your finger . if the card is flicked sharply the coin stays where it is while the card flies off . The larger the mass of the body , the greater is its inertie , i.e the more difficult it is move it when at rest and to stop it when in motion . Because of this we consider that the mass of a body measures its inertia. This is better definition of mass than the one given earlier in which it was stated to be’amount of matter’in a body.Second lawNewton’s second law of motion.when using it two points should be noted. First F is the resultant force causing the acceleration a. Second,F must be in newtons , m in kg and a in meters per second squared , otherwise k is not 1 . The law shows that a will be largest when F is large and m is small . You should know appreciate that when the forces acting on a body do not balance there is a net force which causes a change of motion , i.e the body accelerates or decelerates . If the forces balance, there is no change in the motion of the body . However, there may be a change of shape , in which case internal forces in the body balance the external forces.Third lawIf a body A exerts a force on body B,then body B exerts an equal but opposite force on body A.This is Newton’s third law of motion and states that forces never occur singly but always in pairs as a result of the acion between two bodies . For example , when you step forwards from rest your footpushes backwards on the Earth , and the Earth exerts an equal and opposite force forward on you. Two bodies and two forces are involved. The small force you exerts on the large mass of the Earth but the equal force it exerts on you very much smaller mass auses you to accelerate . Note that the pair of equal and opposite forces do not act on the same body ; if they did, there could never be any resultant forces and acceleration would be impossible . for a book resting on a tble, and the table exerts an equal and opposite upward force on the book; this pair of forces act on different objects.The weight of the book does not form a pair with the upward force on the bok as these two forces act on the same body . An appreciation of the third law and the effect of friction is desirable when stepping from a rowing boat. You push backwards on the boat and, although the boat pushes you forwards with an equal force, it is itself now moving backwards . this reduces your forwards motion by the same amount so you may fall in !