Chapter 3-4a Energy

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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
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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)
WFd(100N)(8m)800Nm800J
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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.
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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

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3-3. Kinetic Energy
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.
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3-4. Potential Energy
Potential energy (PE) is the energy an object has
by virtue of its position. Gravitational
Potential Energy PE mgh
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3-5. Energy Transformations
Energy can be transformed or converted from one
form to another.
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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
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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).
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3-7. Nature of Heat
Count Rumford supported the British in the
Revolutionary War and supervised the making of
cannons. He observed that during the boring
process heat was given off (frictional heat) that
could be used to boil water and could be produced
over and over again from the same piece of metal.
Heat must be energy.
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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
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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.
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3-8. Linear Momentum
Newtons Cradle-an example of the conservation of
linear momentum.
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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.
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3-9. Rockets
Rockets are a version of Newtons third law of
motion as well as the conservation of linear
momentum.
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Chapter 3-4b Energy
3-10. Angular Momentum 3.11 Special
Relativity 3.12 Rest Energy 3.13 General
Relativity
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3-10. Angular Momentum
Angular momentum is a measure of the tendency of
a rotating object to continue spinning about a
fixed axis Lmvr L angular
Momentum mmass circling vvelocity of
rotation rdistance from center The smaller the
r the faster the v. Angular momentum is
conserved.
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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 Footballs
• The earth 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)

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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?v8H98BgRzpOM
Torpedo Gyroscope
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3-10. Angular Momentum
Naval Gyroscopes used to stabilize ships and guns
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3-10. Angular Momentum
Naval Gyroscopes used to stabilize ships and guns
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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)
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3-11. Special Relativity
mo m ? heavier to t / ? slower lo
l / ? shorter
Twin Paradox Muon Experiment


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3.12 Rest Energy
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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
• EPt108W(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

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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.
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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.
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4.2 Energy Consumption
Energy consumption 2003
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Fig.4.5
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4.3 Global Warming

• Greenhouse Effect

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4.3 Global Warming

• Atmospheric CO2
• Controlled by water cycle
• Could increase temperature by 10oC

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4.3 Global Warming
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4.3 Global Warming
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4.3 Global Warming
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Use of Various Fuels
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4.5 Liquid Fuels
Petroleum, a mixture of various hydrocarbons, is
the source of most liquid fuels.
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4.5 Hydroelectric Energy
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4.6 Gas Fuels
Natural gas is largely methane, CH4.
Coal can be gasified
Syngas
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4.6 Natural Gas
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4.7 Solid Fuels
Types of solid fuels include coal, wood, and coke
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4.7 Coal
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4.7 Solid Fuels
Acid rain from sulfur impurities in coal.
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4.8 A Nuclear World
Chernobyl Nuclear Accident
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4.8 A Nuclear World
Chernobyl Nuclear Accident
http//www.ems.psu.edu/radovic/Chernobyl.html
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4.8 A Nuclear World
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4-13. The Future
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Fig. 3.42
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Fig. 3.39
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Fig. 3.40
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Fig. 3.41
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4-13. The Future-Algae Farms to Produce Biofuels
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4-13. The Future-Algae Farms to Produce Biofuels