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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
position
 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
scale
 Thermal = sum of KE &PE on microscopic
scale
 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
electrons
 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
atom.
 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
another.
 Does not include nuclear reactions where
matter is converted to energy, but the total
mass and energy in the universe stays the
same.
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
friction
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)
Electric
in
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

Nonrenewable
 Source that we would use faster than they
can be replaced
 Fossil fuels (oil, coal, natural gas)
 Uranium
 How about wood?
Renewable sources

Hydroelectric
 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
efficient)

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