Transcript Ch. 15 Notes

Chapter 15: Energy
Section 15.1 Energy and Its Forms
Section 15.2 Energy Conversion and
Conservation
Section 15.3 Energy Resources
Section 15.1 Energy and Its Forms
Energy and Work
Work is done when a force moves an object
through a distance.
Energy-the ability to do work
Ie. Energy is transferred by a force moving an
object through a distance.
When work is done on an object, energy is
transferred to that object.
Section 15.1 Energy and Its Forms
Energy and Work
Key Concept: Work is a transfer of energy.
Measured in joules (J)=1 newton-meter
Energy has different forms and comes from
different sources: sunlight, food, etc.
Section 15.1 Energy and Its Forms
Kinetic Energy
Many forms of energy can be classified into two
general types: kinetic and potential energy.
Kinetic energy-the energy of motion
Key Concept: The kinetic energy of any moving
object depends upon its mass and speed.
Section 15.1 Energy and Its Forms
Kinetic Energy
Kinetic energy (KE)=1/2mv2
-m=mass (kg); v=speed (m/s)
**doubling the mass will double the kinetic
energy; doubling the speed will quadruple it
Section 15.1
Section 15.1 Energy and Its Forms
Potential Energy
def.-energy that is stored as a result of position
or shape
Is converted to kinetic energy
Two types: gravitational potential energy and
elastic potential energy
Gravitational-potential energy that depends
upon an object’s height
Section 15.1 Energy and Its Forms
Potential Energy
Key Concept: An object’s gravitational potential
energy depends on its mass, its height, and the
acceleration due to gravity.
Potential energy (PE)=mgh; m=mass,
g=acceleration due to gravity, h=height
Gravitational potential energy is directly related
to the mass of the object and its height .
Section 15.1 Energy and Its Forms
Potential Energy
Elastic potential energy-the potential energy of
an object that is stretched or compressed
“elastic”-something springs back to its original
shape after being stretched or compressed.
Ex. Rubber bands, springs
Section 15.1 Energy and Its Forms
Forms of Energy
Key Concept: The major forms of energy are
mechanical energy, thermal energy, chemical
energy, electrical energy, electromagnetic
energy, and nuclear energy.
Each form can be converted into other forms of
energy.
Section 15.1 Energy and Its Forms
Forms of Energy
mechanical energy -the energy associated with
the motion and position of everyday objects
-mechanical energy does not include thermal
energy, chemical energy, or other forms of
energy
Section 15.1 Energy and Its Forms
Forms of Energy
thermal energy -the total potential and kinetic
energy of all the microscopic particles in an
object.
As an object’s atoms move faster, its thermal
energy increases and the object becomes
warmer.
Objects that are hot enough can emit light.
Section 15.1 Energy and Its Forms
Forms of Energy
chemical energy -the energy stored in chemical
bonds.
When bonds are broken, the released energy
can do work.
All chemical compounds store energy (including
fuels).
Section 15.1 Energy and Its Forms
Forms of Energy
electrical energy -the energy associated with
electrical charges
They can exert forces that do work
electromagnetic energy -a form of energy that
travels through space in the form of waves
(visible light, x-rays)
Electromagnetic waves are often used for
communication b/c they travel long distances.
Section 15.2 Energy Conversion
and Conservation
Energy Conversion
Key Concept: Energy can be converted from
one form to another.
def.-the process of changing energy from one
form to another
Section 15.2 Energy Conversion
and Conservation
Conservation of Energy
When energy changes from one form to another,
the total energy remains unchanged even
though many energy conversions may occur.
Key concept: The law of conservation of energy
states that energy cannot be created or
destroyed.
Section 15.2 Energy Conversion
and Conservation
Energy Conversions
**One of the most common energy conversions
is between potential energy and kinetic energy.
Key Concept: The gravitational potential energy
of an object is converted to the kinetic energy of
motion as the object falls.
Conversions b/t kinetic and potential energy can
happen in both directions.
Section 15.2 Energy Conversion
and Conservation
Energy Conversion in Pendulums
(A weight swinging back and forth from a rope or
string) Ex. clocks
Kinetic energy and potential energy undergo
constant conversion as a pendulum swings.
At highest point, pendulum is briefly motionless
while it changes direction.
The weight of the pendulum at that point has
zero kinetic energy and maximum potential
energy.
Section 15.2 Energy Conversion
and Conservation
Energy Conversion in Pendulums
Pendulum swings down; potential energy is
converted to kinetic energy
Pendulum has maximum kinetic energy and
zero potential energy as it reaches the bottom of
the swing. (process repeats)
Energy Conversion in the Pole
Vault
Refer to Section 15.2 pg. 457
Section 15.2 Energy Conversion
and Conservation
Energy Conversion Calculations
When friction is small enough to be ignored, and
no mechanical energy is added to a system, the
system’s mechanical energy does not change.
ME= KE + PE
Conservation of Mechanical Energy
(KE+ PE) beginning = (KE + PE)end pg. 459
Section 15.2
Section 15.2 Energy Conversion
and Conservation
Energy and Mass
Einstein-developed his theory of relativity in
1905
Key Concept: Einstein’s equation, E=mc2, says
that energy and mass are equivalent and can be
converted into each other.
E=energy; m=mass; c=speed of light
Energy is released as matter is destroyed, and
matter can be created from energy.
However, if was found that mass and energy
together are always conserved (law of
conservation of energy)
Section 15.3 Energy Resources
Nonrenewable Resources
**Energy resources can be classified as either
renewable or nonrenewable
Nonrenewable resources exist in limited
quantities.
Once used, can’t be replaced except over the
course of millions of years.
Key Concept: Nonrenewable energy resources
include oil, natural gas, and uranium.
Section 15.3 Energy Resources
Nonrenewable Energy Resources
Ie. These resources are being used up much
faster than they can be replaced.
fossil fuels -rich deposits of hydrocarbons
formed underground from the remains of onceliving organisms (oil, natural gas, coal, and
uranium)
Majority of the world’s energy use comes from
fossil fuels.
Section 15.3 Energy Resources
Renewable Energy Resources
-def.-resources that can be replaced in a
relatively short period of time
Most originate either directly or indirectly from
the sun. (generating electric power)
Key Concept: Renewable energy resources
include hydroelectric, solar, geothermal, wind,
biomass, and, possibly in the future, nuclear
fusion.
Section 15.3 Energy Resources
Renewable Energy Resources
Hydroelectric Energy -energy obtained from
flowing water
Flowing water is used to turn turbines that are
connected to electric generators.
Advantage: low cost, lack of pollution
Disadvantage: dams cause environmental
problems (fish population)
Section 15.3 Energy Resources
Renewable Energy Resources
Solar Energy -sunlight that is converted into
unstable energy
Used to warm houses, buildings, etc. (Heats
water)
Sunlight can be converted to electrical energy
(calculators)
Adv. Nonpolluting; Dis. Cloudy areas
Section 15.3 Energy Resources
Renewable Energy Resources
Geothermal Energy -thermal energy beneath
Earth’s surface.
Areas near volcanoes: this energy is used to
generate electricity.
Water can be pumped into the ground and be
turned into steam.
Nonpolluting but not widely available
Section 15.3 Energy Resources
Other Renewable Resources
Biomass energy-the chemical energy
stored in living things (can be converted
directly into thermal energy)
Ex. Using wood or peat to heat homes or
cook; corn stalks used for high-energy
alcohol fuel
Section 15.3 Energy Resources
Other Renewable Resources
Hydrogen fuel cells-generate electricity by reacting
hydrogen with oxygen (can be used to convert energy
from renewable resources) Ex. Hydrogen fuel
End product is water so: nonpolluting means for
transporting energy
A form of hydrogen is also most likely raw material for
nuclear fusion (future).
In physics and nuclear chemistry, nuclear fusion is the
process by which multiple nuclei join together to form a
heavier nucleus. It is accompanied by the release or
absorption of energy.
Section 15.3 Energy Resources
Conserving Energy Resources
Key Concept: Energy resources can be
conserved by reducing energy needs and by
increasing the efficiency of energy use.
energy conservation -finding ways to use less
energy or to use energy more efficiently
People should make energy-saving decisions to
reduce the use of resources.