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Aristotle was a Greek Philosopher and was the most prominent product of the educational system developed by Plato. He spent 20 years learning at the institution developed by Plato, known as the Academy. He later became Alexander the Great’s teacher on his return to Macedonia. Aristotle wrote on a range of topics, such as physics, arts, government, biology, politics, and music, and is credited for profoundly shaping medieval physics. His ideas broadened well into the Renaissance, although they were replaced by other scientists and scholars, notably Galileo Galilei, Descartes, and Sir Isaac Newton. Aristotle’s contribution to the field of physics was on matter, motion, optics, and metaphysics, among others (Aristotle, 1961, pp. 3-7).
Aristotle posited that the universe consists of two parts: the terrestrial and the celestial regions and that in Earth, all bodies were made up of a mixture of four types of matter: earth, water, air, and fire. He said that other heavenly bodies past the moon were made of a fifth substance, the quintessence of Aether. Heavy or dense objects such as iron were mainly made of the earth while less heavy objects consisted of a mixture of the four elements (Jones, 2010, para. 4).
The basic postulation in Aristotelian physics was that the natural setting of the sublunary matter is rest, i.e. the first three elements must seek their natural place at rest on Earth unless changed by some impenetrable plane, such as a table. The fourth element (fire), resides somewhere above us, but below the Moon. Thus, the air is a combination of air and fire.
This model gave a simple, perfect justification for falling rocks, rising flames, and the motion of air, but was deficient in clarifying the ‘violent motion’. For example, when a stone is hurled from a sling, it continues to move even after it had left the sling, yet, by Aristotelian physics, the stone’s natural state is rest and should have dropped to the ground soon after leaving the sling. He explained that the air in front of the stone was disturbed, swirled behind and pushed the stone forward, thus the difference between ‘natural’ downward movement and unnatural violent movement.
Aristotle also delved into optics and offered very accurate information regarding the same as compared to the information available then, for example, he was among the first people to write on the workings of the camera. He constructed a device with a dark compartment and with an aperture to let in light and used this device to study the sun. He concluded that the sun would still be shown as a circular object irrespective of the shape of the hole. This has been modified in modern cameras where it is known as the diaphragm. Aristotle also noted that the size of the image depended on the distance between the aperture and the screen (Cooper, 2007, pp. 175)
Another of Aristotle’s contributions to classical physics was on Causality, he asserted that there were four kinds of causes:
- A substance’s material cause is the material that it comprises of, e.g. for a chair, this might be wood, or bronze/ marble for a sculpture;
- A substance’s formal cause is its form, that is, the organization of that substance;
- A substance’s efficient or moving cause is the key cause of the change or rest;
- A substance’s final cause is its purpose or objective, for example, for a seed, it might be a fully-grown plant, for a ball at an incline, this might be sloping to rest at the bottom.
Aristotle’s description of motion was quite dissimilar from that of modern science, as his comprehension of motion was strongly linked to the actuality-potentiality concept he had developed. In simple language, he described motion as the actuality of a potentiality as such. This statement has received numerous interpretations as actuality and potentiality were opposites according to Aristotle, while some said that the addition of the word as such made it harder to understand (Barnes, 1995, pp. 40).
A distinct feature of the Aristotelian theories was their lack of experimentation for proof, rather, they were based on assumptions and natural logic, and this was to contribute to their downfall several years later. Although there was some level of observation in Aristotle’s physics, the core proof was a philosophical approach where the laws of nature were modified to obey a specific philosophical viewpoint. This weakness was to lead to the demise of his ideas by later day scientists such as Galilei Galileo.
Galileo Galilei, born in 1564 in Pisa, Italy, was a physicist, mathematician, and philosopher who made key contributions to classical and modern physics. His accomplishments include improvements to the telescope and the resultant astronomical observations, a feat that earned him the title of the Father of Modern Observatory Astronomy, Physics, and Science. His theoretical and practical work on the motion of objects was a forerunner of classical mechanics later advanced by Sir Isaac Newton.
On astronomy, for which he is best known, Galileo, using his highly improved telescope, observed four of Jupiter’s biggest satellites, and Venus’ orbit around the sun. He was also the first individual to observe that the Milky Way consisted of millions of stars and that the Moon’s surface was uneven and had many craters, opposing Aristotle’s assertion that the moon’s face was smooth. He also observed Pluto but did not identify it as a planet as it was not as bright as Jupiter (Famous Scientists, 2010, para. 3).
Galileo Galilei performed an experiment from the Leaning Tower of Pisa in which he ascertained that the velocity of descent of two objects was not dependant on their mass. This discovery also went against Aristotle’s teachings that the velocity of fall of bodies depended on their relative weights. He performed an experiment using rolling balls and slant planes, which proved the same point: the rate of acceleration of falling or rolling bodies is independent of their mass. Galileo also observed that a pendulum’s oscillations take the same duration of time irrespective of their amplitude i.e. isochronous, an assertion that was later proved almost true. He found out that the square of the period was directly proportional to the length of the pendulum (Hilliam, 2005, pp. 35).
Galileo suggested that a falling object would do so with a regular acceleration, given the resistance of the medium through which it was falling was insignificant, nearly tending to that of a vacuum. He developed an accurate kinematic law for the distance covered during an even acceleration starting from rest, i.e. the acceleration is directly proportional to the square of time that lapses (d ∝ t2). However, this was not a discovery as Nicole Oresme had deduced the same in the 14th century, and Domingo de Soto in the16th. Galileo, however, stated the time-squared law in algebraic form and this was adopted by latter-day scientists.
Galileo set the foundation for Newton’s first law of motion by stating that bodies maintain their velocity except when a force (mainly friction) acts on them, this brought an end to Aristotle’s assertion that bodies naturally reduced speed and stopped unless a force acted on them. His Principle of Inertia stated: “An object moving on a flat surface will continue to do so in the same direction at a uniform speed unless disturbed”. This was integrated into Newton’s first law of motion (Næss, 2002, pp. 112).
In 1632, Galileo gave a physical theory to explain tides due to the movement of the earth. Had this been true, it could have been a strong point for the actuality of earth’s motion. The theory gave the first understanding of the significance of the shapes of ocean basins on the degree and timing of tides, for example, he rightly explained the reason for the minor tides that occur at the center of the Adriatic Sea as contrasted to those at the end. However, his general explanation of the cause of tides was unsatisfactory (Galilei, 1967, pp. 276).
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Galileo Galilei is one of the most prominent and renowned scientists in the history of classical mechanics. He showed the importance of experimentation rather than relying on first principles as had been put forward by Aristotle Aristotle’s word had been recognized as gospel truth and only a few people had ever tried to prove his assertions through experimentation until Galileo arrived! Galileo proved most of Aristotle’s works to be untrue through the many experiments that he carried out and laid the foundation for other scientists such as Einstein Albert and Sir Isaac Newton.
Sir Isaac Newton
Sir Isaac Newton (1642 – 1627) is, by all dimensions, the most influential person and was one of the most original thinkers, along with Einstein Albert, in the development of modern science. He had been regarded as the founder of modern physical science for nearly 300 years, his application of scientific experimentation was as original as his inquests into Mathematical research. These methods led to the demise of the natural philosophy of Aristotle relating to physics. Newton worked on a range of subjects including astronomy, mathematics, optics, mechanics and gravitation, and other non-scientific subjects such as theology, philosophy, and history. He is best known for his three successful laws of motion that changed the face of modern science and gave him the title of Father of Physics (Hall, 1998, para. 1).
Newton did many experiments in optics and led to the discovery of many principles in optics never known before. He studied the refraction of light and showed that a prism could split white light, and that the light could be converted into the original white light. He also demonstrated that the colored light does not alter its properties when it is split into a spectrum and shone on various surfaces. Newton noted that the light remained the same irrespective of the processes it underwent. Therefore, he concluded that color is the consequence of bodies interacting with already-colored light instead of the bodies producing the color themselves. This is referred to as Newton’s theory of color.
Newton’s studies into optics had been due to his desire to improve the performance of telescopes, and these findings made him believe that greater precision could not be achieved in optical instruments based on the refractive principle. He resorted, consequently, to proposals for a reflecting telescope by earlier scientists but never put it into practice. He constructed several reflecting telescope models in which the image was beamed in a concave mirror through. He delivered one of these to the Royal Society and they were amazed. This encouraged him to publish his findings in On Color, which he later broadened into his book, Opticks, but these received widespread criticism from then scientists, among them, Robert Hooke, for his observations went against the widely-held wave theory of light.
In Opticks (1704), Newton posited that light is made up of particles that were refracted when propelled into a denser atmosphere, he used to sound like waves to account for the recurring patterns of reflection and transmission by thin films (Newton, 1704, Bk.II, Props. 12). He mentioned that light consisted of tremendously fine corpuscles, the normal matter was made of coarser particles, and hypothesized that through an alchemical transmutation, substances could be transformed into other substances, for example, base metals could be turned into Gold (Newton, 1704, 8th Query).
In 1679, Newton resumed his work on mechanics, i.e., gravitation and its consequence on the orbits of celestial bodies. He computed the attestation that the elliptical nature of the orbits would be the outcome of a centripetal force. This finding was published in a tract known as De motu corporum in gyrum and sent to the Royal Society and Edmond Halley, his long-time friend and fellow scientist. The tract was later expanded to form the Principia (Newton, 1729, pp. 10), and published in 1687.
In this book, Newton expressed the three laws of motion that were not altered for more than two centuries. The laws illustrate the relationship between the forces operating on a body and its motion. These were as follows:
- 1st Law: “Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it” (NASA, 2010, para. 1).
- 2nd Law: “Force is equal to the change in momentum (mV) per change in time. For a constant mass, force equals mass times acceleration” (NASA, 2010, para. 2).
- 3rd Law: “For every action, there is an equal and opposite reaction” (NASA, 2010, para. 3).
Apart from the three laws, Newton gave a calculus-like formula for the geometrical computation by “first and last ratios”, presented the first analytical method for calculating the speed of sound, deduced the oblateness of the spheroidal shape of the Earth. He also justified the order of the equinoxes, began the gravitational study of non-uniformity in moon’s motion and gave a theory for obtaining the orbits of comets, among others. The Principia was the most important of Newton’s works and made him known internationally. He also acquired many friends, among them royalties, mathematicians, and scientists.
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