Transcript ENERGY

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 = mc2
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/s2) ●m
Remember, g = 9.8 m/s2
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 v2
• 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. Potential
2. Kinetic
A sandwich
1. Potential
2. Kinetic
A ball being thrown through the
air in a projectile path
1. Potential
2. Kinetic
A gallon of gasoline
1. Potential
2. Kinetic
A lawnmower burning a gallon of
gasoline
1. Potential
2. Kinetic
WS
• PEGravitational = m g h
• KE = ½ m v2
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 h1 & v1 is height & velocity at start
and h2 & v2 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?
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Ability to do work
Ability to cause change
Ability to increase energy
Ability to decrease work
At which point is PE at maximum?
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Joules is not the unit for which of these?
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Potential Energy
Kinetic Energy
Work
Force
At which point is KE at maximum?
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