Newtons_2nd_Law_II

Newtons_2nd_Law_II - Physics 211: Newtons Second Law...

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© 2009 Penn State University Physics 211: Lab – Newton’s Second Law Physics 211: Newton’s Second Law Reading Assignment: Chapter 5, Sections 5-9 Chapter 6, Section 2-3 Introduction: Kinematics is the study of how objects move. Dynamics, on the other hand, focuses upon why objects move. Our own human experience tells us that forces have something to do with causing motion. Aristotle developed a theory of motion based completely upon human experience and reason. He stated simply that all motion, even constant velocity, was caused by the existence of forces. Objects at rest, according to Aristotle, had no forces acting upon them. Spontaneous motion, such as letting go of a rock and watching it magically pick up speed as it fell to the earth, was explained by the fact that all objects had a natural place in the universe. A rock’s natural place was on the ground. Therefore, when a person released a rock from their grasp, it automatically returned to its natural place. The force arose from the object being out of its’ “natural” place and wanting to return to its “natural” place. Aristotle, however, never actually verified his theory with experimentation. If he had, he would have found flaws in his thinking. Many people today still hold Aristotelian views. However, Newtonian theory takes a very different stance. The power of Newton’s theories was revealed through their ability to make detailed mathematical predictions about the motion of objects. These predictions have consistently been verified experimentally. Newton hypothesized that forces cause a change in motion, not motion itself. In addition, he carefully distinguished between individual forces and the net force acting on an object. He said that if the Net Force acting on an object was zero, then the object would continue to move with constant velocity. Constant velocity includes two important parts: constant magnitude (speed) and constant direction. [Note: 1) An object at rest is a special case of the speed being equal to zero; 2) A frame of reference is needed to define each of these parts.] In a sense, Newton felt that moving at constant velocity was an object’s “natural place in the universe.” Newton also carefully explained what would happen to an object that experienced a Net Force with a magnitude of something other than zero. net

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This note was uploaded on 10/22/2010 for the course PHYS 211 taught by Professor Staff during the Fall '08 term at Pennsylvania State University, University Park.

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Newtons_2nd_Law_II - Physics 211: Newtons Second Law...

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