phys1441-spring08-032408-post

phys1441-spring08-032408-post - PHYS 1441 Section 002...

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Monday, Mar. 24, 2008 PHYS 1441-002, Spring 2008 Dr. Jaehoon Yu 1 PHYS 1441 – Section 002 Lecture #16 Monday, Mar. 24, 2008 Dr. Jae hoon Yu Potential Energy Conservative and Non-conservative Forces Conservation of Mechanical Energy •P o w e r Today’s homework is homework #8, due 9pm, Monday, Mar. 31!!
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Monday, Mar. 24, 2008 PHYS 1441-002, Spring 2008 Dr. Jaehoon Yu 2 Announcements • Term exam #2 – This Wednesday, March 26, in class – Will cover CH4.1 – CH6.6 – Mixture of multiple choice problems and numeric problems – Practice problems can be found at the URL: http://www-hep.uta.edu/~yu/teaching/spring08-1441- 002/lectures.html • Reading assignment: CH6.9
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Monday, Mar. 24, 2008 PHYS 1441-002, Spring 2008 Dr. Jaehoon Yu 3 Work and Kinetic Energy A meaningful work in physics is done only when the sum of the forces exerted on an object made a motion to the object. What does this mean? However much tired your arms feel, if you were just holding an object without moving it you have not done any physically meaningful work to the object. Mathematically, the work is written as the product of magnitudes of the net force vector, the magnitude of the displacement vector and cosine of the angle between them. Kinetic Energy is the energy associated with the motion and capacity to perform work. Work causes change of KE after the completion Í Work-Kinetic energy theorem W = K = W = Nm=Joule ( ) i F d = J GJ G i ( ) cos i Fd θ JG 2 1 2 mv fi K K = K Δ
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Monday, Mar. 24, 2008 PHYS 1441-002, Spring 2008 Dr. Jaehoon Yu 4 Potential Energy Energy associated with a system of objects Î Stored energy which has the potential or the possibility to work or to convert to kinetic energy What does this mean? In order to describe potential energy, PE, a system must be defined. What are other forms of energies in the universe? The concept of potential energy can only be used under the special class of forces called the conservative force which results in the principle of conservation of mechanical energy . Mechanical Energy Biological Energy Electromagnetic Energy Nuclear Energy Chemical Energy M E These different types of energies are stored in the universe in many different forms!!! If one takes into account ALL forms of energy, the total energy in the entire universe is conserved. It just transforms from one form to another. ii KE PE + = f f KE PE +
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Monday, Mar. 24, 2008 PHYS 1441-002, Spring 2008 Dr. Jaehoon Yu 5 Gravitational Potential Energy When an object is falling, the gravitational force, Mg, performs the work on the object, increasing the object’s kinetic energy. So the potential energy of an object at a height y, which is the potential to do work is expressed as The potential energy is given to an object by the gravitational field in the system of Earth by virtue of the object’s height from an arbitrary zero level m h f m mg h i PE = What does this mean?
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This note was uploaded on 10/21/2009 for the course PHYS phys1441 taught by Professor Dr.jhaehoonyou during the Spring '08 term at UT Arlington.

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phys1441-spring08-032408-post - PHYS 1441 Section 002...

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