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Phys 0174 Fall 2008 - Chapter 08, 4 slides

# Phys 0174 Fall 2008 - Chapter 08, 4 slides - During the...

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1 Chapter 8 Potential Energy and Conservation of Energy In this chapter we will introduce the following concepts: ¾ Potential Energy ¾ Conservative and non-conservative forces ¾ Mechanical Energy ¾ Conservation of Mechanical Energy 2 A B g v o h v o Work and Potential Energy: Consider the tomato of mass m shown in the figure. The tomato is taken together with the earth as the system we wish to study. The tomato is thrown upwards with initial speed v o at point A. Under the action of the gravitational force it slows down and stops completely at point B. Then the tomato falls back and by the time it reaches point A its speed has reached the original value v o . 3 A B g v o h v o During the trip from A to B the gravitational force F g does negative work W 1 = -mgh . Energy is transferred by F g from the kinetic energy of the tomato to the gravitational potential energy U of the tomato-earth system. During the trip from B to A the transfer is reversed. The work W 2 done by F g is positive ( W 2 = +mgh ). The gravitational force transfers energy from the gravitational potential energy U of the tomato-earth system to the kinetic energy of the tomato. UW ∆= The change in the potential energy U is defined as: 4 f o mgh mgh W = gravity DEFINITION OF GRAVITATIONAL POTENTIAL ENERGY The gravitational potential energy PE is the energy that an object of mass m has by virtue of its position relative to the center of the earth. That position is measured by the height h of the object relative to an arbitrary zero level: U mgh = () J joule 1 m N 1 =

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Phys 0174 Fall 2008 - Chapter 08, 4 slides - During the...

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