chapter_2 - Gravity propels a ski jumper down a straight,...

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23 2 CHAPTER Motion In One Dimension OUTLINE 2.1 Displacement 2.2 Velocity 2.3 Acceleration 2.4 Motion Diagrams 2.5 One-Dimensional Motion with Constant Acceleration 2.6 Freely Falling Objects Caron/Corbis Sygma Life is motion. Our muscles coordinate motion microscopically to enable us to walk and jog. Our hearts pump tirelessly for decades, moving blood through our bodies. Cell wall mecha- nisms move select atoms and molecules in and out of cells. From the prehistoric chase of an- telopes across the savanna to the pursuit of satellites in space, mastery of motion has been critical to our survival and success as a species. The study of motion and of physical concepts such as force and mass is called dynamics . The part of dynamics that describes motion without regard to its causes is called kinematics . In this chapter, the focus is on kinematics in one dimension: motion along a straight line. This kind of motion—and, indeed, any motion—involves the concepts of displacement, velocity, and acceleration. Here, we use these concepts to study the motion of objects undergoing constant acceleration. In Chapter 3 we will repeat this discussion for objects moving in two dimensions. The ±rst recorded evidence of the study of mechanics can be traced to the people of an- cient Sumeria and Egypt, who were interested primarily in understanding the motions of heavenly bodies. The most systematic and detailed early studies of the heavens were con- ducted by the Greeks from about 300 B . C .to A . D . 300. Ancient scientists and laypeople re- garded the Earth as the center of the Universe. This geocentric model was accepted by such notables as Aristotle (384–322 B . C .) and Claudius Ptolemy (about A . D . 140). Largely because of the authority of Aristotle, the geocentric model became the accepted theory of the Uni- verse until the 17th century. About 250 B . C ., the Greek philosopher Aristarchus worked out the details of a model of the Solar System based on a spherical Earth that rotated on its axis and revolved around the Sun. He proposed that the sky appeared to turn westward because the Earth was turning eastward. This model wasn’t given much consideration, because it was believed that if the Earth turned, it would set up a great wind as it moved through the air. We know now that the Earth carries the air and everything else with it as it rotates. Gravity propels a ski jumper down a straight, snow-covered slope at an acceleration that is approximately constant. The equations of kinematics, studied in this chapter, can give his position and velocity along the slope at any time.
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24 Chapter 2 Motion In One Dimension The Polish astronomer Nicolaus Copernicus (1473–1543) is credited with initiating the rev- olution that fnally replaced the geocentric model. In his system, called the heliocentric model , Earth and the other planets revolve in circular orbits around the Sun.
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This note was uploaded on 09/14/2009 for the course PHY 303K taught by Professor Turner during the Spring '08 term at University of Texas.

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chapter_2 - Gravity propels a ski jumper down a straight,...

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