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Unformatted text preview: / Physics 295 Introductory Laboratory I Partners Section Date LAB 6: GRAVITATIONAL FORCES And thus Nature will be very conformable to herself and very simple, performing all the great Motions of the heavenly Bodies by the attraction of gravity. . . Isaac Newton (1730) OBJECTIVES · To explore the nature of motion along a vertical line near the earth's surface. · To save the explanatory power of Newton's Laws by inventing an invisible force (the gravitational force) which correctly accounts for the falling motion of objects observed near the earth's surface. · To examine the magnitude of the acceleration of a falling object under the influence of the gravitational force near the earth's surface. · To examine the motion of an object along an inclined ramp under the influence of the gravitational force. · To discover the relationship between mass and weight. Physics Material: Gravitational acceleration, Newton's Law of Universal Gravitation, Newton's Laws of Motion. OVERVIEW You started your study of Newtonian Dynamics in Lab 3 by developing the concept of force. Initially when asked to define forces most people think of a force as an obvious push or pull such as a punch to the jaw or the tug of a rubber band. By studying the acceleration that results from a force when little friction is present, we came up with a second definition of force as that which causes acceleration. These two alternative definitions of force do not always appear to be the same. Pushing on a wall doesn't seem to cause the wall to move. An object dropped close to the surface of the earth accelerates and yet there is no visible push or pull on it. Newton called this "action at a distance." @1993-94P. Laws, D. Sokoloff, R. Thornton Supported by National Science Foundation and the U.S.Dept. of Education (FIPSE) Note: These materials have been modified locally for use in the U of L laboratories. Page 6-1 Page 6-2 Real Time Physics: Active Learning Laboratory V1.40--8/94 The genius of Newton was to recognize that he could define net/orce or combined/orce as that which causes acceleration, and that if the obvious applied forces did not account for the degree of acceleration then other "invisible" forces must be present. A prime example of an invisible force is the gravitational force--the attraction of the earth for objects. When an object falls close to the surface of the earth there is no obvious force being applied to it. Whatever is causing it to move is invisible. Most people rather casually refer to the cause of falling motions as the action of "gravity." What is "gravity"? Can we describe its effects mathematically? Can Newton's Laws be interpreted in such a way that they can be used for the mathematical prediction of motions that are influenced by "gravity"?...
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