dragonblade0's Diaryland Diary ----------------------------------------------------------------------------------------- the laws of motion want to read a physics essay? have a blast. In western culture, Aristotle, Galileo, and Newton played extremely important roles in developing our understanding of dynamics. Aristotle's understanding of motion was the accepted model for almost 2000 years. Then Galileo challenged Aristotle's understanding and came up with the concept of inertia. Newton then expanded on Galileo's work and developed the three laws of motion. Some of these concepts are still in use today. Aristotle (384–322 B.C.), an early Greek philosopher, had many theories as to how motion worked. Primarily, he thought that heavy objects fell faster than lighter ones; he believed that the rate of freefall was directly proportional to the mass. Aristotle also believed that all matter on and near Earth was a mixture of four elements: earth, water, air, and fire. Fire had the highest place of the four, third was air, then water, and finally earth. Each element moved to seek its natural place. Aristotle used this belief to explain why rain fell from the sky: it was water falling from the region of air to join the region of water below it. Similarly, smoke rose to the region of fire, and apples fell from trees. Objects moved in a natural form of motion if they moved to where they were supposed to be, in their natural place. Aristotle believed that objects that moved horizontally were being forced to move because a force was needed to move the objects. For example, displacing a rock requires a force. If the force was to be removed, the objects would almost instantaneously cease to move, for a lack of force applied. Aristotle’s theory of forced motion seems to be relevant to examples still today, making it entirely understandable why these theories were the accepted explanation for so long. Galileo, who lived from 1564–1642, was an Italian astronomer and physicist. He was the first to challenge Aristotle’s theories of motion. Galileo predicted that any two objects, no matter their weight would fall at the same rate, providing there was no air resistance. Galileo didn’t base his theories solely on logic, as the Greek philosophers had done before him. Instead, he was always looking for experiments and results that would prove his theories. This method completely changed science. Experiments today prove that Galileo’s theory was right. Without friction, all objects near the surface of Earth at the same location will fall with the same constant acceleration. The rate of acceleration has been found to be 9.8m/s2. In free fall, an object accelerates at this rate whether it is dropped straight downward or thrown. Galileo also proposed that a force is only necessary to keep an object in motion if another force is present and providing an opposite force. He named this opposing force friction. He believed that any time we move or try to move an object we encounter friction. A heavy box is difficult to drag sideways not because it is in forced motion, but because friction is present. Without friction, an object moving horizontally at constant speed should continue at the same speed forever. Newton was born in the year that Galileo died. Fifty years after Galileo challenged Aristotle’s theory, Newton summarized Galileo’s ideas concerning the motion of stationary and moving objects into three laws still commonly used today. Newton’s first law states that every object will continue in a state of rest or with constant speed in a straight line unless acted on by an unbalanced force. This law simply states that every object at rest will to stay at rest, and every object in motion tends to keep moving in a straight line with constant speed, and to change the speed or direction of the objects motion requires an external unbalanced force. Further explained, when the forces acting on an object are balanced, the object either remains at rest or continues to move at constant speed in a straight line. If an unbalanced force acts on the object, the object accelerates in the direction of the force. As Newton’s first law was based on Galileo’s discoveries, it‘s sometimes called Galileo’s principle of inertia. Newton’s second law states that when a force acts on an object, the object accelerates in the direction of the force. The acceleration is directly proportional to the force and inversely proportional to the mass. This law describes the relationship between a force and the acceleration of a mass. Lastly, Newton stated his third law: whenever one object exerts a force on a second object, the second object exerts a force that is equal in magnitude and opposite in direction on the first object. Newton’s third law is often paraphrased as “for every action force there is an equal and opposite reaction.” However, this isn’t quite correct; because it does not distinguish that the actions and reactions are forces acting on different objects. These 3 laws of motion can be used to explain the motion of a spaceship that starts from rest, fires its’ rockets for a short time, and travels a great distance. When the ship fires it’s rockets, dust particles are expelled. Using Newton’s third and second law it is understood that the force with which the particles are expelled is returned to the spaceship, and therefore causing it to accelerate. Once traveling the desired speed, the rockets can be shut off and the ship will continue traveling, as explained by Newton’s first law- an object will continue in a straight line until otherwise acted upon by an unbalanced force. Finally, it must be realized that space is a vacuum, and therefore there is no friction encountered, meaning the ship will just keep going. It took 3 brilliant people and thousands of years to come up with the understanding of motion we have currently. Each person refined the definition of motion, and even so, we know that these laws begin to fall apart when we get to the tiny world of the atom. We must realize from the journey of Aristotle, Galileo and Newton that it is entirely possible these laws will be modified in the years to come. 9:28 p.m. - 2004-03-28 ----------------------------------------------------------------------------------------- |
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