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

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