ch6 - Chapter 6 Energy and Energy Transfer Introduction to...

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Chapter 6 Energy and Energy Transfer
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Introduction to Energy The concept of energy is one of the most important topics in science Every physical process that occurs in the Universe involves energy and energy transfers or transformations Energy is not easily defined
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Energy Approach to Problems The energy approach to describing motion is particularly useful when the force is not constant A global approach to problems involving energy and energy transfers will be developed This could be extended to biological organisms, technological systems and engineering situations
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Systems A system is a small portion of the Universe We will ignore the details of the rest of the Universe This is a simplification model A critical skill is to identify the system
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Identifying Systems A system may be a single object or particle be a collection of objects or particles be a region of space vary in size and shape
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Environment There is a system boundary around the system The boundary is an imaginary surface It does not necessarily correspond to a physical boundary The boundary divides the system from the environment The environment is the rest of the Universe
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Work The work , W , done on a system by an agent exerting a constant force on the system is the product of the magnitude, F , of the force, the magnitude D r of the displacement of the point of application of the force, and cos q, where q is the angle between the force and the displacement vectors
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Work, cont. W = F D r cos q The displacement is that of the point of application of the force A force does no work on the object if the force does not move through a displacement The work done by a force on a moving object is zero when the force applied is perpendicular to the displacement of its point of application
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Work Example The normal force, n, and the gravitational force, m g, do no work on the object cos q = cos 90° = 0 The force does do work on the object
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Units of Work Work is a scalar quantity The unit of work is a joule (J) 1 joule = 1 newton . 1 meter J = N · m
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More About Work The system and the environment must be determined when dealing with work The environment does work on the system Work by the environment on the system The sign of the work depends on the direction of relative to Work is positive when projection of onto is in the same direction as the displacement Work is negative when the projection is in the opposite direction
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This note was uploaded on 04/02/2010 for the course PHYSICS 6A taught by Professor Koskeshian during the Spring '10 term at UCLA.

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ch6 - Chapter 6 Energy and Energy Transfer Introduction to...

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