Download Chapter 3-4 Energy - Bakersfield College

Chapter 3-4a Energy
3-1. The Meaning of Work
3-2. Power
3-3. Kinetic Energy
3-4. Potential Energy
3-5. Energy Transformations
3-6. Conservation of Energy
3-7. The Nature of Heat
3-8. Linear Momentum
3-9. Rockets
3-10. Angular Momentum
3.11 Special Relativity
3.12 Rest Energy
3.13 General Relativity
3-1. Work
Work equals force times distance. W = Fd
The SI unit of work is the joule.
1 joule (J) = 1 newton-meter (N · m)
W=Fd=(100N)(8m)=800N·m=800J
3-2. Power
Power is the rate at which work is being done:
P = W/t
SI unit of power is the watt.
1 watt (W) = 1 joule/second (J/s)
The kilowatt (kW) is a convenient unit of
power for many applications.
Horsepower
• James Watt
– Perfected the steam engine 200 years ago
– Had to provide a comparison to the work output of a
horse. He found that:
• Typical horse could perform 497 W of work for as much
as 10 hours a day
• Watt increased the standard to 746 W
– 1 horsepower (hp) = 746 W = 0.746 kW
– 1 kilowatt (kW) = 1.34 hp
– Early steam engines ranged from 4-100 hp
3-3. Kinetic Energy
Telekinesis Video 1
Telekinesis Video 2
Energy is that property something has that
enables it to do work.
The energy of a moving object is called kinetic
energy (KE):
KE = ½mv2
where m = mass and v = speed.
KE increases very rapidly with speed because of the v2 factor.
3-4. Potential Energy
Potential energy (PE)
is the energy an object
has by virtue of its
position.
Gravitational Potential
Energy:
PE = mgh
3-5. Energy Transformations
Energy can be transformed or converted from
one form to another.
3-5. Energy Transformations
Types of Energy
1. Kinetic energy
2. Potential energy
3. Chemical energy
4. Heat energy
5. Electric energy
6. Radiant energy
3-6. Conservation of Energy
The law of conservation of energy states that
energy cannot be created or destroyed, although it
can be changed from one form to another.
Matter can be considered as a form of energy;
matter can be transformed into energy and energy
into matter according to the law of conservation of
energy.
Eo = moc2
where Eo = rest energy, mo = rest mass, and c = speed
of light (3x108m/s or 186,000 miles/sec).
Bakersfield College
Physical Science PHSC-B11
Count Rumford
3-7. Nature of Heat
 American (Benjamin Thompson)
Supported British during Revolutionary War
Count Rumford
the
the
Movedsupported
to Britain after war
andBritish
changed hisin
name
to Count
Revolutionary
WarRumford
and supervised the
Supervised making
cannons
making ofcannons.
He observed
that
Observedprocess
heat given offheat
during boring
during the boring
was process
given
off (frictional(frictional
heat)heat)
that could be used to
Heat
could bebe
usedproduced
to boil water, and
could be
boil water and
could
over
and
produced again from the same piece of metal
over again from the same piece of metal.
Conclusion: Heat must be a form of energy
Heat mustbe
energy.
3-8. Linear Momentum
Linear Momentum is a measure of the tendency of
a moving object to continue in motion along a straight
line:
p = mv
3-8. Linear Momentum
The law of
conservation of
momentum states: In
the absence of
outside forces, the
total momentum of a
set of objects remains
the same no matter
how the objects
interact with one
another.
3-8. Linear Momentum
Newton’s Cradle-an
example of the
conservation of
linear momentum.
3-9. Rockets
The momentum of
the exhaust gases is
balanced by the
rocket's upward
momentum.
Multistage rockets are more
efficient than single-stage, and
so are widely used.
3-9. Rockets
Rockets are a version of Newton’s
third law of motion as well as the
conservation of linear momentum.
3-10. Angular Momentum
Angular momentum
is a measure of the
tendency of a
rotating object to
continue spinning
about a fixed axis
L=mvr
L= angular Momentum
m=mass circling
v=velocity of rotation
r=distance from center
The smaller the “r” the faster
the “v”. Angular momentum
is conserved.
3-10. Angular Momentum
• Definition:
– The more angular momentum an
object has, the greater its
tendency to continue to spin
(and be stable)
• Toy tops
• The earth
• Footballs
• Bullets
– Defining angular momentum is
complicated; depends on…
• How fast the object is turning
• Mass of the object
• How the mass is distributed (the
further the mass is from the center
of the object, the greater the
angular momentum)
3-10. Angular Momentum
Gyroscopes
The Segway
Due to angular
momentum, when a
force is applied in one
direction, the
combined forces,
including the angular
momentum, will be in
a perpendicular
direction.
http://www.youtube.com/
watch?v=GeyDf4ooPdo
3-10. Angular Momentum
Naval Gyroscopes used to
stabilize ships and guns
Naval Ship Stabilization
Naval Gyroscopes used to
stabilize ships and guns
3-11. Special Relativity
Albert Einstein (1879-1955) published the special
theory of relativity in 1905.
Special relativity is based on two postulates:
1. The laws of physics are the same in all frames of
reference moving at constant velocity.
2. The speed of light (c ) in free space has the same
value for all observers (c = 3 x 108 m/s)
3-11. Special Relativity
mo = m γ heavier
to = t / γ slower
lo = l / γ shorter
••
Twin Paradox
Muon
Experiment
3-11. Special Relativity
Twin Paradox
http://www.youtube.
com/watch?v=qgCNDpt-mw
http://www.youtube.c
om/watch?v=DWKn
_Punrjk
http://www.youtube.com/
watch?v=gdRmCqylsME
Muon Experiment
3.12 Rest Energy
3.12 Rest Energy
• E = mc2 or Energy and Mass are the same!
• Example 3.8 p 91
– How much mass is converted to energy
in a 100MW nuclear power plant?
T=(60)(60)(24)= 86,400 s/day
E=Pt=108W(86,400 s/day)=8.64 x 1012J
m = E/c2 = 8.64 x 1012J/(3 x 108m/s)2
m = 9.6 x 10-5kg or about 0.000013 oz
3-13. General Relativity
General theory of relativity was developed by
Einstein in 1916, which related gravitation to the
structure of space and time and showed that even
light was subject to gravity.
Chapter 4 Energy
4-2 Energy Consumption
4.3 Global Warming
4.4 Greenhouse Effect
4.5 Liquid Fuels
4.6 Natural Gas
4.7 Coal
4.8 A Nuclear World
4.13 The Future
4.1 The Energy Problem
1. Oil and natural gas reserves will last about another
century..
2. Although coal reserves will last several hundred more
years, mining coal is dangerous, and burning coal creates
environmental problems such as acid rain, air pollution,
and enhanced global warming.
3. The potential for a large-scale nuclear accident is
present.
4. Discharge of radioactive wastes into the environment
from badly run nuclear power plants has occurred.
5. An unsolved disposal problem of radioactive nuclear
waste exists.
4.2 Energy Consumption
Energy consumption 2003
Fig.4.5
4.3 Global Warming
• Greenhouse Effect
31
4.3 Global Warming
• Atmospheric CO2
 Controlled by water cycle
 Could increase temperature by 10oC
32
4.3 Global Warming
4.3 Global Warming
4.3 Global Warming
4.3 Global Warming
4.3 Global Warming
4.3 Global Warming
Use of Various Fuels
4.5 Liquid Fuels
Petroleum, a mixture of various hydrocarbons,
is the source of most liquid fuels.
4.5 Hydroelectric Energy
4.6 Gas Fuels
Natural gas is largely
methane, CH4.
Syngas
Coal can be
gasified
4.6 Natural Gas
4.7 Solid Fuels
Types of solid fuels include coal, wood, and
coke
4.7 Coal
4.7 Solid Fuels
Acid rain from sulfur impurities in coal.
4.8 A Nuclear World
Chernobyl Nuclear Accident
4.8 A Nuclear World
Chernobyl Nuclear Accident
http://www.ems.psu.edu/~radovic/Chernobyl.html
4.8 A Nuclear World
4-13. The Future
Fig. 3.42
Fig. 3.39
Fig. 3.40
Fig. 3.41
4-13. The Future-Algae Farms to
Produce Biofuels
4-13. The Future-Algae Farms to
Produce Biofuels