chapter5 - Chapter5 Energy FormsofEnergy 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
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    Some Energy Considerations Energy can be transformed from one form to  another The total amount of energy in the Universe never  changes 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 Provides a link between force and  energy The work,  W , done by a constant force  on an object is defined as the product of  the component of the force along the  direction of displacement and the  magnitude of the displacement
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    Work W = F  x This equation applies  when the force is in  the same direction  as the displacement                 are in the  same direction and F x r r
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    Work General W = (F cos  θ ) F is the magnitude of  the force Δ x is the magnitude  of the object’s  displacement θ  is the angle  between  and F x r r
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    Work, cont. This gives no information about The time it took for the displacement to  occur The velocity or acceleration of the object Work is a scalar quantity
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    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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    More About Work The work done by a force is zero when  the force is perpendicular to the  displacement cos 90° = 0 If there are multiple forces acting on an  object, the total work done is the  algebraic sum of the amount of work  done by each force
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    More About Work, cont. Work can be positive or negative Positive if the force and the displacement  are in the same direction Negative if the force and the displacement  are in the opposite direction
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    When Work is Zero Displacement is  horizontal Force is vertical cos 90° = 0
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    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, Final Work doesn’t happen by itself Work is done  by  something in the  environment,  on  the object of interest The forces are constant Varying force will be discussed later
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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 
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This note was uploaded on 07/19/2010 for the course PHYS 212 taught by Professor Sadler during the Spring '10 term at New Mexico.

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chapter5 - Chapter5 Energy FormsofEnergy Mechanical...

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