The study of physics has been a quest that has been traversed by generations of human beings on the journey to explain their physical environment. Today the laws of physics encompass a vast body of phenomenon from cosmic events to toaster ovens to tiny atoms. These laws were not always so accurate and are a result of constant evolution through the development of ideas and scientific methods, maybe even toady we are all horribly wrong about the nature of the universe and the next big leap is lying just around the corner.
The evolution of one of the fundamental ideas of physics is what I am taking into consideration here; motion. Motion is a part of our everyday lives, from locomoting to the bus stop to the blood gushing around in our arteries. Even though it seems like a relatively simple concept its evolution had been a long one, fraught with misconceptions and strokes of genius as well.
Today we explain motion as a continuous change in the position of a body relative to a reference point, as measured by a particular observer in a particular frame of reference.
Two models are in common use today, the Newtonian model and the special relativistic model.
But more than a thousand years ago things were different
Physical science went hand in hand in philosophy as can be seen in Aristotle’s {382 - 322 bc} description of motion as “any kind of change” and the “actuality of a potentiality”. He also believed that the substances making up the Earth were different from the substance making up the heavens, which meant that he had a different set of laws for the motion of objects on earth and the motion of celestial spheres. This sort of division seems impractical in today science as we stress on finding laws, which are applicable to a wide variety of phenomenon. It must be remembered though, that the tools for examining physical phenomenon outside our atmosphere were almost non-existent at that time. He also taught that dynamics (the branch of physics that deals with motion) was primarily determined by the nature of the substance that was moving.
The rest of Aristotle theories can be summed up as:
All motion on the Earth being linear.
All motion in the heavens (outer space) being curved.
The speed at which an object falls is directly related to the mass of an object.
Motion could be considered in two main factions: natural and violent.
Motion continues so long as there is only an applied motion to an object. Removing the motion stops the object.
A glance at these postulates awakens surprise and even laughter in my mind, but as always we must keep in mind the lack of advanced scientific tools for measurement. All physics is constructed by postulation followed by accurate experimentation and the collation of the results into a sound theorem. Aristotle possessed few scientific tools other than his eyes and ears. Thus linear motion seems rather plausible if he had no way to measure the motion of a projectile in two dimensions simultaneously as we can do these days. Telescopes had not been developed thus Aristotle’s views on celestial motion could not hope to be accurate without, observational evidence. It seems like common sense for an iron ball to reach the ground before a feather; Aristotle had neither vacuum chamber nor a proper concept of gravitation or inertia to help him see past this obvious blunder. The ideas of friction and inertia eluded him, leading him to believe that removing an applied motion stops a body.
The evolution of these ideas into Galileo’s {1564 – 1642 AD) more accurate picture shows me the importance of scientific tools. Galileo was able to create a more accurate picture of motion in space because of the development of the telescope, which allowed him to make extensive observations and records of the motion of planets. His concept of inertia was quite contrary to Aristotle's ideas of motion and the idea of frictional forces helped him properly analyze why some objects {like a block of wood} stopped moving once a force was removed and why other objects {like an arrow} continued moving because of little friction from the air and plenty of inertia. These differences {between a block of wood and an arrow} had thoroughly puzzled Aristotle leading him to draw drastically incorrect conclusions. Applying these concepts Galileo also managed to dispel the famous myth that objects of different masses fell with different accelerations as the story of the leaning tower of Pisa experiment suggests. It would be foolish to say though, that Aristotle’s contributions were useless, the nature of any evolution is such that there must be a foundation {even if it is incorrect} on which new, different ideas can be built upon. Aristotle had made the vital contribution of taking the first brave steps towards humanities understanding of motion and physics.
The most important piece of the puzzle for our modern understanding of motion in engineering and everyday life is Isaac Newton’s (1642-1727) contributions in the form of his laws of motions. Again these were built upon Galileo’s theories but like all forms of evolution, it provided a more insightful picture to the puzzle of motion. Newton took the huge leap of suggesting that the laws that governed the heavens were the same laws that governed motion on the surface of the Earth. He went on to make the vital contribution of providing a solid body of mathematics on which motion could be accurately calculated. This allowed him to integrate the ideas of motion into three laws thus putting an end to the compartmentalization of the various ideas of motion that had plagued humanity before. Newton’s contributions ranged form carrying out thousand of painstaking experiments to verify his mathematical description of motion to helping in the development of calculus for more complex types of motion
In the Newtonian model, because motion is defined as the proportion of space to time, these concepts are prior to motion, just as the concept of motion itself is prior to force. In other words, the properties of space and time determine the nature of motion and the properties of motion, in turn, determine the nature of force.
Newton’s laws can be summarized as:
1.An object will maintain its state of rest or constant speed in a straight line unless acted upon by an external unbalanced force
2.) When an external unbalanced force is applied to an object at rest or in constant speed in a straight line, the object accelerates in the direction of the unbalanced force. Furthermore, the acceleration of the object is directly proportional to the net forces acting on the object, and inversely proportional to the mass of the object being accelerated (F=ma) "
3.) When an object exerts a force on a second object, the second object will exert a force of equal magnitude, and opposite direction on the first object
Newton also went on to create a more concrete idea of friction, based on Galileo’s ideas {again here we see the importance of basing ideas on previous concepts and how ideas can evolve and develop down the ages}
Newton’s laws seemed to be the final step in humanities understanding of motion as they are perfect at physically and mathematical describing motion at a day to day level adequate for engineering and other human activities.
But no story in physic ever has an end, there will always be something deeper and more magnificent lying below what we already know, humanity can only begin to scratch the surface of the true reality and nature of the universe.
Einstein and Euclidean geometry made the next big leaps from Newtonian motion, speaking of relative motion *1 and the space-time theory, this paved the way for quantum physics pioneered by physicists such as Heinsberg and perfected by geniuses such as Richard Fennyman.
Who knows what the next big leap will be.. Maybe we will complete a full circle back to the philosophies from where we once started. Maybe Zeno was right all along in his idea that there is no such thing as motion and everything in the universe is one…
*1 In the special relativistic model, motion can be thought of as something like an angle between a space direction and the time direction. In special relativity and Euclidean space, only relative motion can be measured, and absolute motion is meaningless.
Bibliography
Physics “cutnell and Johnson”
http://library.thinkquest.org
http://en.wikipedia.org/
http://www.iep.utm.edu/a/aris-mot.htm
http://csep10.phys.utk.edu/astr161/lect/history/newton.html
http://galileoandeinstein.physics.virginia.edu/lectures/aristot2.html
http://www.britannica.com/eb/article-33175/Aristotle
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