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CH7%20Energy%20of%20a%20system

# CH7%20Energy%20of%20a%20system -...

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CH7_Energy of a System.notebook 1 Jun 21­3:57 PM CHAPTER 7: ENERGY OF A SYSTEM Oct 18­4:59 PM Chapter Outline 7.1 Systems and Environments 7.2 Work Done by a Constant Force 7.3 The Scalar Product of Two Vectors 7.4 Work Done by a Varying Force 7.5 Kinetic Energy and the Work– Kinetic Energy Theorem 7.6 Potential Energy of a System 7.7 Conservative and Nonconservative Forces 7.8 Relationship Between Conservative Forces and Potential Energy 7.9 Energy Diagrams and Equilibrium of a System Oct 18­5:03 PM Oct 18­4:59 PM Systems A system is a small portion of the Universe. We will ignore the details of the rest of the Universe. A critical skill is to identify the system. The first step to take in solving a problem A valid system: May be a single object or particle May be a collection of objects or particles May be a region of space May vary with time in size and shape Section 7.1 Oct 18­4:59 PM System Example A force applied to an object in empty space System is the object Its surface is the system boundary The force is an influence on the system from its environment that acts across the system boundary. Section 7.1 Oct 18­4:59 PM Displacement in the Work Equation The displacement is that of the point of application of the force. If the force is applied to a rigid object that can be modeled as a particle, the displacement is the same as that of the particle. For a deformable system, the displacement of the object generally is not the same as the displacement associated with the forces applied. Section 7.2

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CH7_Energy of a System.notebook 2 Oct 18­4:59 PM Work Example The normal force and the gravitational force do no work on the object. cos θ = cos 90° = 0 The force is the only force that does work on the object. Section 7.2 Oct 18­4:59 PM More About Work The sign of the work depends on the direction of the force relative to the displacement. 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. The work done by a force can be calculated, but that force is not necessarily the cause of the displacement. Work is a scalar quantity. The unit of work is a joule (J) 1 joule = 1 newton . 1 meter = kg ∙ m² / s² J = N m Section 7.2 Oct 18­4:59 PM Scalar Product of Two Vectors The scalar product of two vectors is written as . It is also called the dot product. • θ is the angle between A and B Applied to work, this means Section 7.3 Mar 24­2:22 PM Jun 21­12:33 PM Oct 18­4:59 PM Dot Products of Unit Vectors Using component form with vectors: In the special case where Section 7.3
CH7_Energy of a System.notebook 3 Mar 24­2:33 PM Jun 21­12:39 PM Oct 19­9:44 AM Jun 21­12:49 PM Jun 21­12:54 PM Mar 24­2:45 PM

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CH7_Energy of a System.notebook 4 Mar 24­3:02 PM Oct 18­5:22 PM Oct 18­5:41 PM
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CH7%20Energy%20of%20a%20system -...

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