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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.
PEint + KEint = PEfinal + KEfinal
PE = 10000 JKE = 0 J
PE = 7500 JKE = 2500 J
PE = 5000 JKE = 5000 J
PE = 2500 JKE = 7500 J
PE = 0 JKE = 10000 J
PE = 10000 JKE = 0 J
PE = 7500 JKE = ?
PE = 5000 JKE = ?
PE = 2500 JKE = ?
PE = 0 JKE = ?
Mechanical and Non Mechanical Energies
• If there are non-mechanical energies involved in a system, energy is still conserved.
PEint + KEint = PEfinal + KEfinal + 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)
PEint + KEint = PEfinal + KEfinal + 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
Energy – Flow Chart
Energy
Mechanical Non-mechanical
Light Sound HeatKinetic Potential
Linear
Rotational
Gravitational
Elastic
Electric
Magnetic
