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15.1 Energy and it’s forms
Work = force x distance
 Work = transfer of energy
 Kinetic Energy= KE= ½ mv2
 Mass in kilograms, velocity in meters/sec
 Kg m2/s2 we call a joule
 Pg 448 problems 1-3
15.1 Energy and it’s forms
Gravitational Potential energy = PE
 PE= mgh sometimes called energy of
 Elastic potential- like a rubber band or ball
 Why doesn’t a ball bounce as high as you
drop it from?
Forms of Energy
Mechanical =Sum of KE and PE on large
 Thermal = sum of KE &PE on microscopic
 As atoms move and bounce into each other
more, their thermal energy increases
 Thermal (heat) and temperature are related
Forms of Energy
Chemical energy – energy stored in the
bonds between atoms of a compound
 Gasoline has stored chemical energy
 Takes energy to rip bonds apart, energy is
given off when bonds are formed
Forms of Energy
Electrical- electricity is the movement of
 These charged particle can produce a force
on other particles to cause work to be done
 Electromagnetic- normally we think of this
as radiation. Examples- light, X-ray, IR, UV
 Sound Energy
Forms of Energy
Nuclear Energy – energy stored within the
 The forces that hold an atom together and
the actual conversion of small amounts of
mass into great quantities of energy
 E= mc2
 Page 452, questions 4,5,6,7
15.2 energy conversion
Law of Conservation of Energy
 Energy cannot be created or destroyed, it
can only be converted from one form to
 Does not include nuclear reactions where
matter is converted to energy, but the total
mass and energy in the universe stays the
Energy Conversion
Example of a Pendulum
 PE is converted to KE, then back to PE
 Why does it slow down?
 Where does the energy go?
Ans. To heat the air and the pendulum thru
Energy Flow diagram
Example of an electric drill
 Energy in- electrical thru the cord
 Energy out- mechanical to turn drill bit,
sound, heat
Efficiency –comparing the wanted energy
coming out to the total energy going in.
Mechanical (120 J)
Heat (45 J)
(200 J)
Sound (35 J)
Efficiency ?
Efficiency = work out over work in (or the
usable energy out divided by the total
energy put in)
 120 J of work out
 200 J of work in
 120/200 = 0.60 or 60% efficient
Flow diagram for a light bulb?
Flow diagram for a car engine ?
 (car engines are only up to 30% efficient)
15.3 Resources
 Source that we would use faster than they
can be replaced
 Fossil fuels (oil, coal, natural gas)
 Uranium
 How about wood?
Renewable sources
 Uses potential energy of rivers, or tides and
waves to spin generators
 Solar
 Can be either to convert to thermal energy
or to convert to electric. (thermal more
Geothermal- can be used to collect thermal,
 Can also be used to convert thermal into
mechanical, into electrical
 Wind- used to convert KE (caused by
thermal) to mechanical, then to electric
 Biomass- radiant to chemical to thermal,
and maybe to mechanical to electrical
 Hydrogen fuel cell- chemical to electrical