Most Helpful Customer Reviews
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6 of 6 people found the following review helpful:
5.0 out of 5 stars
Excellent book, April 25, 2002
This book is a fascinating overview of the history of mechanics. One learns just how much was known about mechanics before the time of Galileo, and the facts are surprising. The work of Galileo and Newton was not a sudden leap in knowledge of mechanics, but grew out of work done in the middle ages and in ancient times. Here are just a few of the highly interesting historical facts that are expounded on in the book: 1. The work of Plato, who held that the weight of an object was the result of a force that was pushing it downwards. 2. The approach of Aristotle to mechanics: he was much more elaborate than Plato, and he made an intensive effort to understand the origin of motion fundamentally. The Aristotelian conception of motion and dynamics can be summarized as follows. There are two kinds of motion, natural and violent. Aristotle gives the falling body as an example of natural motion, whereas projectile motion is an example of violent motion. Violent motion has the property of being temporary, and objects undergoing violent motion will eventually undergo natural motion. Natural motion is in turn divided up into two classes: celestial motion and terrestrial motion. Objects that undergo celestial motion are characterized by what is now called uniform circular motion. On the other hand, terrestrial motion is rectilinear, and for Aristotle rectilinear motion is either straight up or straight down. An object needs a force and a resistance acting on it if it is to be in motion. Heavy bodies fall faster than light ones. Aristotle refused to admit the existence of a vacuum since such a void would not sustain the motion of an object. In addition, a total vacuum would offer no resistance to the motion of an object, and thus the object would, according to Aristotle, move off with increasing speed. In a vacuum he concluded that heavy bodies would move with the same speed as light ones, again unacceptable he argued. 3.In the sixth century, the philosopher John Philoponus gave what is probably the first systematic attack on the Aristotelian ideas of motion. He argued that the planetary motions, as confirmed by observation, are much more complex than the simple circular motion that Aristotle imputed to them. Philoponus also proposed the so-called "impetus theory" to explain projectile motion. As the name implies, according to this theory the thrower imparts an impressed force or impetus to the projectile which keeps it moving until the "natural" motion and the resistance of the medium takes over. The projectile then falls straight down. The power given to the projectile by the impetus will gradually damp out because of the resistance of the medium and these "natural tendencies" of the projectile. 4. A somewhat more axiomatic and mathematical approach to mechanics in the thirteenth century was proposed by Jordanus of Nemore. His work is interesting in that it contains a notion of virtual work, a concept that was really not developed extensively (and proven to be practically useful) until the nineteenth century. Jordanus also attempted to quantify the idea of acceleration, and in his writings he deduced that an object accelerates when, in a fixed interval of time, a greater amount of space is covered by the object, and so when the speed of the object increases. Jordanus discussed this in the context of falling objects, but he did not in his writings relate the distance the object falls in terms of the time it took the object to fall. As for the cause of the acceleration of the object, Jordanus held to the view that as the object descended, the object caused the air surrounding it to be less resistive, thereby causing the body to accelerate. Lastly, and most interestingly from the standpoint that it occured during the thirteenth century, an anomynous author of a work entitled Liber Jordani de ratione ponderis solved correctly the problem of the equilibrium of a heavy body on an inclined plane. 5. John I. Buridan of Bethune (1300 - 1358) developed a theory of the impetus which rejected the idea that air is the motive power for projectiles, Buridan took the impetus to reside permanently in the projectile, until the object is acted upon by some other forces. This belief of Buridan regarding the impetus is very important from a modern standpoint, because it is somewhat similar to the idea of inertia that was developed in the sixteenth and seventeenth centuries. In Buridan's view a heavy body would receive more of the impetus than a lighter one. Buridan gave as an example the difference in impetus gained from a heavy iron versus that of light wood. If two objects, one of wood and one of iron have the same volume and the same shape, then the iron object will be moved farther because it will have a greater impetus imparted to it. 6. The ideas of Buridan were discussed by Albert of Saxony (1316 - 1390). He held basically the same beliefs as Buridan about impetus and projectile motion, free fall, etc. Albert concluded that the speed of a falling object increases as the distance of the fall. Most interesting is that he used the idea of impetus to treat the problem of a stone dropped through a hole in the Earth, and concluded that the motion of the stone would oscillate about the center of the Earth until the impetus in the stone was exhausted. 7. Noted work on mechanics in the fourteenth century was performed by logicians at Merton College. One individual of this school was William Heytesbury, who distinguished between the velocity of an object and the measure of how much the velocity is changing: the acceleration of the object. Heytesbury gave definitions of uniform velocity, uniform acceleration, and instantaneous velocity, but these were not correct from the standpoint of modern mechanics. He rejected the Aristotelian ideas on free fall, noting that a falling body travels three times as far in the second second of its fall as in the first.
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6 of 12 people found the following review helpful:
4.0 out of 5 stars
Very good, but ...., October 6, 2000
This book is refered by the publishers as the best book on history of mechanics. Indeed, it is a very complete work, showing in cronological order all the developments and contributions made by a great number of scientists and mathematicians, many of them famous but including also many not-so-famous and even not known. The book is very well written. However, when I bought this book I was expecting something more informal, more enjoyable to read. The feeling I have is that the book is somewhat too formal, arid, like the common textbooks. Although, it is still a very fine, very good book, and I suggest that every physics student to read it.
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1 of 19 people found the following review helpful:
5.0 out of 5 stars
Necessary Reading For All Believers In God , June 13, 2006
This book is important today because it deals with the poorly developed concept of `impetus.'' Impetus is defined as the motion that bodies have acquired from a motive agency. Today, the nature of the motive agency divides nonbelievers from the believers. Believers say that God is the motive agency that produces the impetus in all bodies of the universe. On the other hand, nonbelievers say that the motive agency of all bodies in the universe is an infinitely dense physical thing called the Big Bang. So, the believers say that the motive agency is spiritual whereas the nonbelievers say that it is physical.
Dugas opens his book with Aristotle's thoughts on motion. Aristotle divides all motions into natural or violent. For instance, the motion of a stone in a sling is natural. The motion of the stone becomes violent when the stone is released from the sling and becomes a projectile. Aristotle also says that the motive agency is always in contact with its moving bodies but is not a part of the moving bodies. Contact means that the motive agency and the moving bodies coexist.
Since Aristotle's universe has no vacuums, when a stone becomes violent and moves through air, for instance, the stone forces air out of the space it consumes and new air fills the empty space as the stone moves forward. Aristotle thought that the motion of the new air moves the stone forward until the projectile falls to the ground due to the attraction of gravity. As seen, Aristotle's motive agency is physical.
William of Ockham (1300-1350) was the first to reject Aristotle's theory of motion. But, he offers no alternative theory. Jean Buridan (1300-1358), a student of Ockham at the University of Paris, argues that the motive agency is spiritual. However, Buridan expected theologians to show how God acts as the motive agency of all bodies in the universe.
Theologians eventually showed that God is the motive agency of all moving bodies. First, Nicole Oresme (1329-1382), a mathematician and theologian, became the forerunner of the analytical geometry of Descartes when he argued that every measurable thing has a continuous quantity. Oresme's argument says that a motive agency, spiritual or physical, must coexist continuously with the motions it produces. This argument cannot be met with the Big Bang theory because the infinitely dense physical particle becomes nonexistent upon its explosion. On the other hand, God is permanent and is thus in continuous contact with all bodies in the universe.
Nicholas of Cusa (or Cues) was the first to show how God is in continuous contact with all things found in the universe. He shows this contact by developing a positive and negative science out of precise symbols... In this science, all opposites coincide in God. Thus, `what is not moving' and `what is moving' coexist continuously. Cusa's writings inspired the cosmologies of Copernicus and Kepler, Bruno's monads, Da Vinci's `forza,' the deism of Isaac Newton and the work of Leibniz. In Part II (Chapter Two), Leibniz distinguishes dead forces and living forces. The dead forces are expressed with the calculus and the equation d (m v2/2) = F ds. When this equation is integrated, living forces are born from the dead forces. The integrating process forms the fundamental law, m dv/dt = F.
In a new book entitled 'The First Scientific Proof of God, I conclude that God creates bodies with spiritual atoms. The spiritual atoms are one in God, are immortal and are endless in number. At creation, the spiritual atoms become distinct, different and related. Their relations form one universe with many organized bodies (stones, water, bees, horses, plants, humans, etc). The spiritual atoms enter and leave bodies at different rates continuously. This is why all organized bodies age and die. The permanency (immortality) and the motions of the spiritual atoms are guided by a complex differential equation that only God can know. We can only gain better understandings of God's Intelligent Design. In my book, I show that it is natural for all bodies to change continuous (aging, etc). Thus I view a continuum of motion as a continuum of rests. Thus, one's death is only a rest in a continuous processes that includes reincarnation. God also rests, as Moses concluded in his creation theory. But, God's rests are wise changes..
Interestingly, The Notebooks of Leonardo Da Vinci by Dover Publications (1970) shows that Da Vinci protected his thoughts about Cusa with complex coding schemes. Thus, the truths in Dan Brown's book on The Da Vinci Code can questioned. Galileo also studied Cusa. But, Galileo did not secure his research results as Leonardo did.. Eventually, the Roman Church charged Galileo with heresy and was imprisoned, after he agreed with Cusa that the universe has no center body and that planet earth is not the center of the universe, as taught by the Church.
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