8 - Potential Energy and Conservation of Energy

# 8 Potential - Chapter 8 Potential Energy CHAPTE R OUTLI N E 8.1 Potential Energy of a System 8.2 The Isolated System Conservation of Mechanical

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Potential Energy CHAPTER OUTLINE 8.1 Potential Energy of a System 8.2 The Isolated System— Conservation of Mechanical Energy 8.3 Conservative and Nonconservative Forces 8.4 Changes in Mechanical Energy for Nonconservative Forces 8.5 Relationship Between Conservative Forces and Potential Energy 8.6 Energy Diagrams and Equilibrium of a System 217 ± A strobe photograph of a pole vaulter. During this process, several types of energy transforma- tions occur. The two types of potential energy that we study in this chapter are evident in the photograph. Gravitational potential energy is associated with the change in vertical position of the vaulter relative to the Earth. Elastic potential energy is evident in the bending of the pole. (©Harold E. Edgerton/Courtesy of Palm Press, Inc.) Chapter 8

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I n Chapter 7 we introduced the concepts of kinetic energy associated with the motion of members of a system and internal energy associated with the temperature of a sys- tem. In this chapter we introduce potential energy , the energy associated with the conﬁg- uration of a system of objects that exert forces on each other. The potential energy concept can be used only when dealing with a special class of forces called conservative forces . When only conservative forces act within an isolated sys- tem, the kinetic energy gained (or lost) by the system as its members change their rela- tive positions is balanced by an equal loss (or gain) in potential energy. This balancing of the two forms of energy is known as the principle of conservation of mechanical energy . Potential energy is present in the Universe in various forms, including gravita- tional, electromagnetic, chemical, and nuclear. Furthermore, one form of energy in a system can be converted to another. For example, when a system consists of an electric motor connected to a battery, the chemical energy in the battery is converted to kinetic energy as the shaft of the motor turns. The transformation of energy from one form to another is an essential part of the study of physics, engineering, chemistry, biology, geology, and astronomy. 8.1 Potential Energy of a System In Chapter 7, we deﬁned a system in general, but focused our attention primarily on single particles or objects under the inﬂuence of an external force. In this chapter, we consider systems of two or more particles or objects interacting via a force that is inter- nal to the system. The kinetic energy of such a system is the algebraic sum of the ki- netic energies of all members of the system. There may be systems, however, in which one object is so massive that it can be modeled as stationary and its kinetic energy can be neglected. For example, if we consider a ball–Earth system as the ball falls to the ground, the kinetic energy of the system can be considered as just the kinetic energy of the ball. The Earth moves so slowly in this process that we can ignore its kinetic energy.
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## This note was uploaded on 02/24/2011 for the course PHYS 102 taught by Professor Wang during the Spring '11 term at Nanjing University.

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8 Potential - Chapter 8 Potential Energy CHAPTE R OUTLI N E 8.1 Potential Energy of a System 8.2 The Isolated System Conservation of Mechanical

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