Download 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 its natural state,
• and how much it wants to return to that
natural state
• Good examples:
• Springs, swings, pendulums, rubber
bands
Kinetic Energy
• This is the KE released by an object by
its motion
• KE = ½ m v2
• Joules = kg●(m/s)2
Problems
• A 3.0-kilogram toy dump truck moving
with a speed of 2.0 m/s starts up a
ramp. How high does the truck roll
before it stops?
• A 2.0-kilogram ball rolling along a flat
surface starts up a hill. If the ball
reaches a height of 0.63 meters, what
was its initial speed?
Problems
• Find the potential energy of this roller
coaster when it is halfway down the hill.
• A 2.0-kilogram ball is tossed straight up
with a kinetic energy of 196 joules. How
high does it go?
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
• Most common energy conversion is from
potential to kinetic energy
• Gravitational potential energy of an
object is converted to kinetic energy as
the object falls.
• Potential energy can become kinetic and
vice versa.
• Example: Pendulums
Mechanical Energy in a Pendulum
• Einstein’s famous equation
• E = mc2
• m = mass
• c = speed of light (3 x 108 m/s)
• Shows that matter can be
converted into energy and energy
can be converted into mass.