Transcript Document

Energy
• Energy is the capacity to
do work or produce heat
or change
• The study of energy and
its transformations is
known as thermodynamics
• Objects, from baseballs
to molecules, can produce
energy
energy
• Chemical energy of substances is due
to the potential energy stored in the
arrangements of their atoms…coal,
gasoline, hydrogen
• Thermal energy the total amount of
energy from the movement of particles
in matter; the atoms in matter are
always moving; the more motion, the
more thermal energy; heat and thermal
energy are not the same…heat is
transferred, thermal energy is a
quantity
• Mechanical Energy: energy that moves
objects; mechanical energy is the sum
of kinetic and potential energy
• Sound Energy vibrations of states of
matter
• Electromagnetic Energy: Energy that
can travel through empty space in
waves…light falls under this
• Nuclear Energy: energy that has its
source in the nucleus of an atom…can
result from fusion or fission
• **Other forms of energy, like
electricity, will fall under these**
Energy: Mechanical(Kinetic and Potential)
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Kinetic energy is energy in motion
Kinetic energy increases as the speed of an object increases…also increases with
increasing mass
(Ek = ½ mv2): mass x (velosity)2
Potential energy is stored energy that results from the attraction and repulsions
an object experiences in relation to other objects
Potential energy can be gravitational, chemical, nuclear, or elastic
Potential energy due to gravity is GPE = mgh (mass x gravitational acceleration
(9.8 m/s2) x height)
Potential energy can be converted into kinetic energy
Mechanical energy = Potential energy + Kinetic energy
Units of Energy
• The unit for energy is the joule (“jool”)
• A mass of 2 kg moving at a speed of 1 m / s possesses a kinetic energy
of 1 Joule (1 J)
• A joule is not a large amount of energy and is often expressed in kJ
• Energy changes in chemical reactions will sometimes be expressed in
calories (cal)
• 1 calorie = 4.184 J EXACTLY and is the amount of energy needed to
raise 1 g of water 10 C
• The specific heat of an object is the amount of energy it takes to raise
the temperature of the substance one degree Celsius…the greater the
specific heat, the more energy required to raise its temperature
Law of Conservation of Energy
• Like matter, Energy
can neither be created
nor destroyed, it can
only change form…This
is the LAW OF
CONSERVATION OF
ENERGY
• Energy is conserved, it
changes form!!!
• Energy will be
transferred from high
to low
• No energy transfer is
100% efficient
Renewable vs. Non renewable
To Flipchart
• Non-renewable energy sources cannot be replenished (made again) in a
short period of time. Examples include: coal, petroleum, natural gas,
propane, nuclear, and oil
• Renewable energy sources can be replenished naturally in a relatively
short period of time. Examples include: water, geothermal, wind, solar, and
biomass
• Secondary energy sources are those that come from the conversion of
other sources of energy, like coal, natural gas, oil, nuclear power and other
natural sources, which are called primary sources.
Energy
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Energy is transferred in two general ways: to cause motion of an object
against a force, or to cause a temperature change…pg 81 of your book
A force is any kind of push or pull on an object
Work is energy used to cause an object to move against a force; work = force x
distance moved W = fd; units are Joules
Heat is the energy transferred from a hotter object to a colder one; thermal
energy and heat are not the same! The transfer of heat results in an increase in
thermal energy!
Energy Efficiency is a measurement of how much energy is converted in to a
desirable form than is released into the surroundings; energy
Energy Efficiency = output
input
TEMPERATURE AND
PARTICLE MOVEMENT
• Everything around you has kinetic energy
even if it is not in motion…the atoms are
moving
• The Kinetic theory of matter states
that all of the molecules that make up
matter are constantly in motion
• Remember how particles behave in the
states of matter!!!
• Temperature is a measure of the average
kinetic energy of all molecules in an
object…it is not possible to know the
kinetic energy of each individual molecule
• If something is said to have a high temp.
that means its molecules are moving fast
and have a high average kinetic energy
• When something warms, its molecules
speed up; when something cools, they slow
down…soup cools when its molecules
collide with the air molecules above it
• Remember that kinetic energy =
(½ mass x velocity2); it goes for molecules
too!!!! KE = mv2…doorknobs don’t have to
move as fast as air
Direction of heat
transfer
• Heat is the flow of energy from an
object of high temperature to one of
low temperature…when an object
gives off heat, that means it is
transferring energy!! Heat is energy
in transit
• Thermal energy is the total kinetic
energy of molecules in an object…all
the kinetic energy is added together!
• Thermal energy and temperature are
different, why?
• As heat is transferred, thermal
energy can go up or down, how?
• When a system absorbs heat, it is
said to be endothermic (endo = into)
• Ice melting is an endothermic
process
• Ice feels cold because it is absorbing
heat from our hand, the surroundings
• The release of heat is called an
exothermic process (exo = out of)
• Heat flows out of the system and into
the surroundings
Energy / Heat transfer
• Conduction is the direct
transfer of heat through
touching of solid
objects…objects that
transfer heat easily are good
conductors
• Insulators do not transfer
energy easily, there are
spaces between their
molecules
• Convection is the transfer of
energy through the movement
of particles in a liquid or an
gas
• Radiation is energy that
travels as electromagnetic
waves…it is unique in that it
can travel through empty
space
• Heat can be transferred by
conduction, radiation, and
convection
Temperature
Scales
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F = (9/5C) + 32
o
• The choice of a temperature
scale is arbitrary, meaning it
is not bound by rules
• A scientist who made
especially good thermometers
was Gabriel Fahrenheit
(1686-1736)…he devised his
own temperature scale
• Celsius, named after its
inventor Anders Celsius
(1701-1744) a Swedish
Astronomer. It has the
freezing point of water at sea
level being 0 degrees Celsius,
and the boiling point at sea
level 100 degrees C
• Thermometers measure temp.
by a variation of physical
properties of the liquid
inside…the liquid will expand
with a rise in temperature
(thermal expansion)
C = 5/9(F – 32)
The
Kelvin
Scale
K = oC + 273
• SI unit for temperature is
Kelvin
• Named after an English
physicist and mathematician,
Lord Kelvin (William Thomson)
(1824-1907)
• The degree symbol (o) is not
used
• However, one degree Kelvin is
the same size as one degree
Celsius
• The difference between Kelvin
and Celsius is the location of
the zero point (0C +273.15 K)
• 0 K, or absolute zero, is the
point at which the motion of
particles of matter, their
kinetic energy, is gone!!