Chapter 3-4a Energy 3-1. The Meaning of Work 3-2. Power 3-3. Kinetic Energy 3-4. Potential Energy...

Chapter 3-4a Energy

3-1. The Meaning of Work3-2. Power3-3. Kinetic Energy3-4. Potential Energy3-5. Energy Transformations3-6. Conservation of Energy3-7. 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. WorkWork 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

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.

Telekinesis Video 1Telekinesis Video 2

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.

Types of Energy1. Kinetic energy2. Potential energy3. Chemical energy4. Heat energy5. Electric energy6. Radiant energy

3-5. Energy Transformations

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).

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.


Linear Momentum is a measure of the tendency of a moving object to continue in motion along a straight

line:

p = mv


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.


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.

Rockets are a version of Newton’s third law of motion as well as the conservation of linear momentum.

3-9. Rockets

3-10. Angular Momentum

Angular momentum is a measure of the tendency of a rotating object to continue spinning about a fixed axis L=mvrL= angular Momentumm=mass circling v=velocity of rotationr=distance from centerThe 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 • 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)

3-10. Angular MomentumGyroscopes

The SegwayDue 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 MomentumNaval 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)


mo = m γ heavier

to = t / γ slower

lo = l / γ shorter

••

Twin Paradox

Muon Experiment


Twin Paradox Muon Experiment

http://www.youtube.com/watch?v=gdRmCqylsME

http://www.youtube.com/watch?v=DWKn_Punrjk

http://www.youtube.com/watch?v=qgC-NDpt-mw

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 Consumption4.3 Global Warming4.4 Greenhouse Effect4.5 Liquid Fuels4.6 Natural Gas4.7 Coal4.8 A Nuclear World4.13 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

31

• Greenhouse Effect

4.3 Global Warming

32

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

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

http://www.ems.psu.edu/~radovic/Chernobyl.html

Chernobyl Nuclear Accident

4.8 A Nuclear World

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

Chapter 3-4a Energy 3-1. The Meaning of Work 3-2. Power 3-3. Kinetic Energy 3-4. Potential Energy...

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Transcript of Chapter 3-4a Energy 3-1. The Meaning of Work 3-2. Power 3-3. Kinetic Energy 3-4. Potential Energy...