ENERGY THE DRIVING FORCE What is Energy The

ENERGY THE DRIVING FORCE

What is Energy? • The ability to do work The ability to cause change • Measured in Joules, just like work • Formula Symbol: E • • as in E = mc 2

Forms of Energy • Mechanical Energy • Describes energy stored and released according to function or force

Forms of Energy • Electromagnetic Energy • Waves of mostly invisible energy • Includes light, radio waves, X-rays

Forms of Energy • Chemical Energy • Stored and released in the bonds between atoms

Forms of Energy • Nuclear Energy • Stored and released from the nucleus of an atom

Forms of Energy • Thermal Energy • Heat in all its forms and flows

Two descriptions of Energy • • Potential Energy • Energy stored by position or condition Kinetic Energy • Released energy or energy of motion

Potential Energy • • • The easiest quantified PE is Gravitational PE This is the PE stored in an object by its height above another reference point PEGravitational = m g h Joules = kg●(m/s 2) ●m Remember, g = 9. 8 m/s 2

Potential Energy, revisited… • • Another form is Elastic PE This is the PE stored in an object by its being disturbed from is natural state, and how much it wants to return to that natural state Good examples: • Springs, swings, pendulums, rubber bands

Potential Energy, revisited… • • Another form is Chemical PE This is the PE stored in an object by the chemical bonds between its atoms and molecules The energy is released when the chemicals react and form new bonds Good examples: • Burning a log, firecrackers,

Kinetic Energy • • • This is the KE released by an object by its motion KE = ½ m v 2 Joules = kg●(m/s)2

Potential or Kinetic? • On the next few slides, tell whether the energy is potential or kinetic…

A bowling ball rolling down the lane 1. 2. Potential Kinetic

A sandwich 1. 2. Potential Kinetic

A ball being thrown through the air in a projectile path 1. 2. Potential Kinetic

A gallon of gasoline 1. 2. Potential Kinetic

A lawnmower burning a gallon of gasoline 1. 2. Potential Kinetic

WS • • PEGravitational = m g h KE = ½ m v 2

Mechanical Energy • • • Total amount of KE and PE in a system As PE decreases, KE increases As KE decreases, PE increases m g h 1 + ½ m v 12 = m g h 2 + ½ m v 22 Where h 1 & v 1 is height & velocity at start and h 2 & v 2 is height & velocity at end

Law of Conservation of Energy • • • Energy can not be created or destroyed in normal reactions Energy can be changed from one form to another The total amount of energy must be the same before and after a change in energy

Mechanical Energy in a Pendulum

Which of these describes Energy? 1. 2. 3. 4. Ability to do work Ability to cause change Ability to increase energy Ability to decrease work

At which point is PE at maximum? 1. 2. 3. 4. A B C D

Joules is not the unit for which of these? 1. 2. 3. 4. Potential Energy Kinetic Energy Work Force

At which point is KE at maximum? 1. 2. 3. 4. A B C D