# Chapter 5 - Chapter 5 Energy Forms of Energy Mechanical...

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Chapter 5 Energy

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Forms of Energy Mechanical Focus for now May be kinetic (associated with motion) or potential (associated with position) Chemical Electromagnetic Nuclear
Some Energy Considerations Energy can be transformed from one form to another Essential to the study of physics, chemistry, biology, geology, astronomy Can be used in place of Newton’s laws to solve certain problems more simply

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Work F is the magnitude of the force Δ x is the magnitude of the object’s displacement θ is the angle between x ) cos F ( W θ and F x r r
Units of Work SI Newton • meter = Joule N • m = J J = kg • m 2 / s 2 US Customary foot • pound ft • lb no special name

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When Work is Zero Displacement is horizontal Force is vertical cos 90° = 0
Work Can Be Positive or Negative Work is positive when lifting the box Work would be negative if lowering the box The force would still be upward, but the displacement would be downward

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Work and Dissipative Forces Work can be done by friction The energy lost to friction by an object goes into heating both the object and its environment Some energy may be converted into sound For now, the phrase “Work done by friction” will denote the effect of the friction processes on mechanical energy alone
Kinetic Energy Energy associated with the motion of an object Scalar quantity with the same units as work Work is related to kinetic energy 2 mv 2 1 KE =

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Work-Kinetic Energy Theorem When work is done by a net force on an object and the only change in the object is its speed, the work done is equal to the change in the object’s kinetic energy Speed will increase if work is positive Speed will decrease if work is negative net f i W KE KE KE = - = ∆
An object’s kinetic energy can also be thought of as

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## This note was uploaded on 04/16/2008 for the course PHY 1603 taught by Professor Boudreaux during the Spring '08 term at The University of Texas at San Antonio- San Antonio.

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Chapter 5 - Chapter 5 Energy Forms of Energy Mechanical...

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