# Energy 12/11/14. Chapter 6 – Work and Energy Major Concepts: Work Power Conservative and Non-Conservative Forces Mechanical and Non-Mechanical Energies.

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Energy 12/11/14

Chapter 6 – Work and Energy Major Concepts: Work Power Conservative and Non-Conservative Forces Mechanical and Non-Mechanical Energies Work-Energy Theorem Conservation of Energy

Work Positive work – If a component of the force is in the same direction as the displacement Negative work – If a component of the force is in the opposite direction as the displacement No work – If the force is perpendicular to the displacement OR there is no displacement

Energy 12/11/14

Chapter 6 – Work and Energy Major Concepts: Work Power Conservative and Non- Conservative Forces Mechanical and Non-Mechanical Energies Work-Energy Theorem Conservation of Energy

Energy Energy: (scalar) The property of an object or a system that enables it to do work Unit: Joules (J)

Energy Potential energy: Energy due to relative position or location of objects –Gravitational PE –Elastic PE Kinetic energy: Energy due to the motion of an object

Potential Energy Gravitational Potential Energy Elastic (Spring) Potential Energy Electrical Potential Energy

Energy Mechanical energy: The sum of the kinetic energy and potential energy of a system. Non-mechanical Energy: is internal energy that takes place on the molecular level

Energy (cont.) Mechanical energy: Potential Energy Kinetic Energy Non-mechanical Energy: Thermal energy (heat) Sound (Vibrational) energy Radiant (Light) energy Chemical energy Nuclear energy

Work-Energy Principle (Theorem) Work-Energy Principle: states that the net work done on an object by the net force is equal to the change in its kinetic energy:

Law of Conservation of Energy Law of Conservation of Energy: Energy can not be created or destroyed, but it can be transformed from one form to another, the total amount never changes.

Mechanical Energy If there are no non-mechanical energies or non-conservative forces involved in a system, then mechanical energy can transform from one energy to another. PE int + KE int = PE final + KE final

PE = 10000 J KE = 0 J PE = 7500 J KE = 2500 J PE = 5000 J KE = 5000 J PE = 2500 J KE = 7500 J PE = 0 J KE = 10000 J PE = 10000 J KE = 0 J PE = 7500 J KE = ? PE = 5000 J KE = ? PE = 2500 J KE = ? PE = 0 J KE = ?

Mechanical and Non Mechanical Energies If there are non-mechanical energies involved in a system, energy is still conserved. PE int + KE int = PE final + KE final + TE

Conservation of Energy For objects falling or going down a hill Gravitational potential energy is being transferred into kinetic energy and thermal energy (if friction and air resistance is accounted for) PE int + KE int = PE final + KE final + TE

Law of Conservation of Energy and Non-Conservative Forces If there is any change in the total mechanical energy of an object (whether a gain or a loss), then you know for certain that there is a non-conservative force doing work to conserve the energy

True / False Questions #10-36

Conservation of Energy

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