Energy

1
Chapter 3

• Energy

2
Work

• Work (W) is concerned with the application of
  force (F) to an object and the distance (d) the
  object moves as a result of the force.
• W F x d

3
What is Energy?

• Energy is the ability to do work.
• One way of classifying energy is as potential
  energy (PE) and kinetic energy (KE).

4
Potential Energy

• The energy that an object has because of its
  position.
• Types of potential energy
• Gravitational Potential Energy-Due to the
  attraction of object to the earth.
• When a person raises a book the work that the
  person does on the book is stored on the book as
  potential energy. The book now has the potential
  of doing work on something else.
• When a spring is stretched the work done to
  stretch the spring is now stored as potential
  energy. The spring now has the potential of doing
  work on something else.

5
Potential Energy

• Work done on Increase Increase in
• an object to in PE work the
  object
• change its can do
• position
• Work on book PE of book Work by book

6
Fig. 3.2
7
The Joule

• The joule is a measure of work accomplished on an
  object.
• It is also a measure of potential energy or how
  much work an object can do.
• In the English system the unit of work and energy
  is the ft x lb.
• F m x a For a falling object a g, so
• F m x g
• Energy is force x distance.
• E F x d
• For a falling object dh (hheight)
• E F x h
• PE m x g x h

8
Potential Energy

• The potential energy of an object can be
  calculated from the work done on the object to
  change its position.
• You can exert a force equal to its weight as you
  lift it some distance above the floor.
• Weight is the force of gravity acting on a mass.
• You can exert a force equal to its weight as you
  lift it some height above the floor, and the work
  you do is a product of its weight and height.

9
Potential Energy and Weight

• Weight mass x acceleration due to gravity
• w m x g
• Work weight x height
• W w x h
• PE w x h
• PE m x g x h

10
Fig. 3.3
11
Units for Energy

• W F x d
• W Kg x m / s2 x m
• N x m
• Joules (J)

12
Calculation of Potential Energy

• How much potential energy does a backpack have if
  it has a mass of 6.7 kg and is sitting on a shelf
  1.8 m above the floor?
• m 6.7 kg PE m x g x h
• g 9.8 m/s2
• PE 6.7 kg x 9.8
  m/s2 x 1.8 m
• h 1.8 m PE 118 kg x m x m
• PE ? s2
• PE 118 N x m or
  118 J

13
Calculation of Work

• How much work is needed to raise a box to a shelf
  which is .56 m above the ground if the box has a
  mass of .75 kg?
• m .75 kg PE m x g x h
• h .56 m PE .75 kg x 9.8 m/s2 x .56 m
• g 9.8 m/s2 PE 4.1 kg x m2
• PE ?
  s2
• W PE 4.1 N x m 4.1 J

14
Kinetic Energy

• Moving objects have the ability to do work on
  other objects because of their motion.
• The energy of motion is kinetic energy.
• It can be measured in terms of
• 1. Work done to put the object in motion
• or
• 2. Work the moving object will do in
• coming to rest.

15
Kinetic Energy

• If you throw a football you exert a force on it
  as you accelerate it through a distance before it
  leaves your hand.
• The kinetic energy the ball now has is equal to
  the work, or force times distance, that you did
  on the ball.
• The ball exerts a force on the hand of the person
  catching the ball and moves it through a
  distance.
• The net work on the hand is the kinetic energy
  that the ball had.
• Work done to Increase Increase in
• put object in in KE work the
  
• motion
  object can do

16
Kinetic Energy
17
(No Transcript)
18
Kinetic Energy

• If a bowling ball with a mass of 5.25 kg is
  thrown with a velocity of 7.3 m/s, what is the KE
  of the ball?
• m5.25 kg KE1/2 mv2
• v7.3 m/s KE1/2 (5.25 kg)(7.3 m/s)2
• KE ? KE 140 kg x m2/s2
• 
  
• KE 140 J

19
Kinetic Energy

• A football player with a mass of 115 kg moving
  with a velocity of 8.5 m/s tackles a stationary
  quarterback. How much work was done on the
  quarterback?
• m115 kg WKE ½ mv2
• v8.5 m/s W ½ (115 kg)(8.5 m/s)2
• W ? W4154 J

20
Kinetic and Potential Energy Conversion

• A roller coaster is a good example of kinetic and
  potential energy conversion.
• When a roller coaster is going up work is done on
  it. When it is at the top the work that was done
  on it is stored as potential energy.
• When the roller coaster starts going down the
  potential energy is converted to kinetic energy.

21
Forms of Energy

• Another way to classify energy is as follows
• Sources of Energy common today. The first three
  are currently much more widely used globally
• 1. Chemical
• 2. Radiant
• 3. Nuclear
• 4. Hydropower
• 5. Wind Power
• 6. Biomass
• 7. Geothermal Energy
• Manifestations of energy ( The above energies can
  be converted to the following)
• 1. Mechanical
• 2. Electrical

22
Mechanical Energy

• Energy of familiar objects and machines.
• e.g. a.) car moving is kinetic mechanical
• energy.
• b.) water behind a dam is potential
• mechanical energy.
• c.) spinning blades of a steam turbine
• is kinetic mechanical energy.

23
Chemical Energy

• Form of energy involved in chemical reactions.
• e.g. 1.) oxidation reduction reactions such
• as burning wood. (rapid oxidation)
  
• release the chemical energy
• stored in wood.
• 2.) foods you eat are oxidized in your
  
• body and the energy is later
• released as you move, etc.
• 3.) Batteries release energy stored in
  chemical
• compounds through oxidation
  reduction reactions
• which is then converted to
  mechanical or
• electrical energy and used to
  power
• miscellaneous devices.

24
Fig. 3.11
Chemical Energy
Mechanical Energy
25
Photosynthesis

• Photosynthesis, which occurs in green plants, is
  a process through which plants use the energy of
  the sun to rearrange carbon dioxide (CO2) and
  water (H2O) into glucose and oxygen
• Energy Carbon Dioxide Water Glucose
  Oxygen
• Glucose is used to make Cellulose (Wood) and
  starch (potatoes, etc..)
• http//earthguide.ucsd.edu/earthguide/diagrams/pho
  tosynthesis/photosynthesis.html
  

26
Burning of Wood

• Wood Oxygen Carbon Dioxide
• Water Energy
• This is the reverse of photosynthesis.
• Chemical energy is potential energy which is
  stored in molecules and later released in a
  chemical reaction.

27
Radiant Energy

• Energy that travels through space. This is light
  or sunlight (visible light)

28
Radiant Energy

• Visible light occupies a small portion of the
  electromagnetic spectrum which makes up radiant
  energy.
• Infrared radiation is heat. Objects heat up when
  this type of radiation is absorbed.
• Microwave radiation is used in cooking.

Increases
Increases
29
Electrical Energy

• Another form of energy from electromagnetic
  interactions. It can travel through wires to your
  home from a power plant.

30
Nuclear Energy

• Energy found in the nucleus of the atom.

31
Power Plants

• Electrical Turbine-Converts chemical or nuclear
  energy to electrical energy
• Steam Turbines
• In a power plant, chemical or nuclear energy
  is used to heat water to steam, which is directed
  against the turbine blades.
• The mechanical energy of the turbine turns an
  electrical generator.
• Chemical Mechanical Electrical
• or Nuclear

32
Interconversion of Energy

• Any form of energy can be converted to another
  form. Most technological devices are energy form
  converters.

33
Inter conversion of Energy

• A light bulb coverts electrical energy to radiant
  energy.
• A car converts chemical energy from gasoline to
  mechanical energy.
• A solar cell converts radiant energy to
  electrical energy.
• An electrical motor converts electrical energy to
  mechanical energy.
• Each technological device converts some form of
  energy, usually chemical (from batteries) or
  electrical to another form that you desire,
  usually mechanical (fan) or radiant (light bulb).

34
Flow of Energy

• Plants are at the bottom of the food chain. They
  get their energy by converting radiant energy
  from the sun to chemical energy.
• You get the energy from plants and animals, who
  in turn got their energy from plants.
• When you ride a bicycle the bicycle has KE as it
  moves along. The bicycle got its KE from you.
• The bicycle converts its KE to heat (infrared
  radiation) when you apply brakes or through
  friction with the road surface.
• The infrared radiation is then released onto
  space.
• The radiant energy from the sun comes from
  nuclear reactions that take place in the core of
  the sun.

35
(No Transcript)
36
Energy Conservation

• Total energy content in the universe is constant.
  
• The ultimate source of all energy is the sun.
• Einsteins equation, Emc2, where c is the speed
  of light, relates mass and energy. So ultimately
  all energy comes from the mass of the sun.

37
The Law of Conservation of Energy

• Energy can neither be created nor destroyed. It
  can only be converted from one form to another,
  but the total amount of energy remains constant.

38
Energy Sources TodayChemical Energy

• Fuels are things that can be burned to produce
  energy. (Chemical sources of energy)
• The first fuel that was used was wood.
• Coal started to be used in the industrial
  revolution.
• In the twentieth century petroleum is the main
  fuel.
• The fuels that we use today correspond to
• Petroleum 40
• Natural gas 23
• Coal 21
• Biomass 3
• (Material from
• Photosynthesis)

This equates to 89 of all energy
consumed. About 1/3 of this energy was burned for
heating and the rest was burned to drive
engines or generators.
39
History of Energy Sources

• The energy source mix has changed from past years
  and it will change in the future.
• Wood supplied 90 of the energy until the 1850s
  when the use of coal was increased.
• By 1910 coal was supplying 75 of the energy.
• Then petroleum began making increased
  contributions to the energy supply.
• Now increased environmental and economic
  constraints and decreasing supply of petroleum
  are producing another supply shift.

40
Energy Sources Today

• Nuclear energy and hydropower are non chemical
  sources of energy.
• They can be used to generate electrical energy.
• Solar and geothermal energy are alternative
  sources of energy as well and they provide about
  .5 of all energy consumed.

41
Energy Sources Today

• In summary, the main sources of energy today are
• 1. Fossil fuels (Chemical Energy)
• Petroleum
• Natural Gas
• Coal
• Biomass
• 2. Hydropower
• 3. Nuclear
• 4. Solar
• 5. Geothermal
• 6. Wind Power

42
(No Transcript)
43
Petroleum and Natural Gas

• Petra Rock Oleum Oil
• Petroleum is oil that comes from oil bearing
  rock.
• Natural Gas has a similar origin. Both come from
  organic sediments, materials that have settled
  out of bodies of water.
• Most organic material is from plankton, tiny free
  floating animals and plants such as algae. They
  accumulate and sometimes a local condition
  permits the accumulation of sediments that are
  particularly rich in organic materials.
• Petroleum and Natural Gas formed from the remains
  of tiny organisms that lived millions of years
  ago.

44
Petroleum and Natural Gas

• Bacteria, pressure, appropriate temperature and
  time are all important for petroleum formation,
  but it is not well understood.
• Natural gas is formed at higher temperatures than
  petroleum.
• Petroleum forms a thin film around the grains of
  the rock where it formed. Pressure from the
  overlying rock and water move the petroleum and
  gas through the rock until it reaches a rock type
  structure that stops it.
• If natural gas is present it will occupy the
  space above the accumulating petroleum.

45
Petroleum and Natural Gas

• One barrel of oil 42 US gallons.
• The supply of petroleum and natural gas is
  limited. Most of the continental drilling
  prospects appear to be exhausted and the reach
  for new petroleum supplies is now offshore. Over
  25 of our nations petroleum is estimated to
  come from offshore wells.
• Imported petroleum accounts for more than half of
  the oil consumed, with most coming from Mexico,
  Canada, Venezuela, Nigeria, and Saudi Arabia.

46
Uses of Petroleum

• 45 Gasoline
• 40 Diesel
• 15 Heating Oil
• Other uses
• Making medicine
• Clothing fabrics
• Plastics
• Ink

47
Coal

• Coal formed from an accumulation of plant
  materials that collected under special conditions
  millions of years ago.
• Plants died and sank. Stagnant swamp water
  protected the plants and plant materials from
  consumption by animals and decomposition by
  microorganisms.
• Over time chemically altered plant materials
  collected at the bottom of pools of water in the
  swamp. This carbon rich material is peat. It is
  used as fuel in many places.
• Under pressure and high temperatures peat will
  eventually be converted to coal.
• Coal contains impurities which leave an ash when
  it is burned. One of the impurities is sulfur,
  which produces a pollutant, sulfur dioxide, a
  contributor to acid rain.

48
Moving Water

• Used as a source of energy for thousands of
  years.
• Considered a renewable energy source,
  inexhaustible as long as rain falls.
• Today hydroelectric plants generate 3 of the
  nations total energy consumption at about 2,400
  power generating dams across the nation.
• In 1940 hydropower furnished 40 of the US
  electric power. Today 9. It is projected to
  drop to 7 in the future.
• Geography limits the number of sites that can be
  built.
• Water from reservoir is conducted through large
  pipes called penstocks to a powerhouse, where it
  is directed against turbine blades that turn the
  shaft on an electric generator.

49
(No Transcript)
50
Nuclear

• Energy is released as the nucleus of uranium and
  plutonium atoms split or undergo fission. This
  takes place in a reactor, a large steel vessel.
  Water is pumped through the reactor to produce
  steam, which is used to produce electrical
  energy.
• Radioactivity is a danger associated with nuclear
  power plants.

51
(No Transcript)
52
Energy Usage

• To provide 1 MW(1 million watts or 1 thousand
  kilowatts), which supplies the electrical needs
  of 1,000 people for 1 hour, you would need
• 1000 lbs of coal
• 80 gallons of oil
• 9000 cubic ft of gas
• .13 g uranium

53
Pollution

• Byproducts of burning petroleum products, coal,
  and natural gas are pollutants such as carbon
  monoxide (poisonous), excessive amounts of carbon
  dioxide and water vapor (lead to global warming),
  and acid rain caused by sulfur and nitrogen
  oxides and also by carbon dioxide from exhausts
  from engines.
• Byproducts of nuclear power plants are the
  dangers of nuclear radiation escaping and the
  disposal of the nuclear waste.
• Hydropower, solar power, and wind power dont
  produce pollution but have the disadvantage of
  either not being readily available, such as
  hydropower and wind power, or not being very
  efficient (all three).

54
Energy Sources Tomorrow

• Solar Energy
• Solar Cells-A thin crystal of silicon, gallium,or
  some polycrystalline compound that generates
  electricity when exposed to light. They have no
  moving parts and produce electricity directly,
  without the need for hot fluids or intermediate
  conversion states. Used in space vehicles and
  satellites. On earth they are limited because of
  the manufacturing cost. Used in watches and
  calculators.
• Passive Application Energy flows by natural
  means without mechanical devices such as motors
  or pumps. Solar energy is captured, stored, and
  distributed throughout a house.

55
Energy Sources Tomorrow

• Solar Energy
• Active application- Requires a solar collector in
  which sunlight heats water, air, or some liquid.
  The liquid or air is pumped through pipes in a
  house to generate electricity or used directly
  for hot water.
• Power tower-Heliostats (special mirrors) surround
  a tower and focus sunlight on a boiler at the top
  of the tower. A mixture of salts, potassium
  nitrate and sodium nitrate, will be heated to
  about 566oC and melted. It wil then be pumped to
  a steam generator just like other power plants.
  Water could be heated directly in the power tower
  boiler. Molten salt is used because it can be
  stored in an insulated storage tank for use when
  the sun is not shining.

56
Energy Sources Tomorrow

• Wind Energy-Has been used for centuries to move
  ships, grind grain into flour, and pump water.
  Wind turbines are used to generate electrical or
  mechanical energy. The problem is the
  inconsistency of wind.
• Biomass-Any material formed by photosynthesis,
  including small plants, trees, and crops, and any
  garbage, crop residue or animal waste. It can be
  burned directly as a fuel, converted into a gas
  fuel (methane), or converted into liquid fuels
  such as alcohol. The problems include the energy
  expended in gathering the biomass and to convert
  it to a gaseous or liquid fuel.

57
Energy Sources Tomorrow

• Geothermal energy-Energy from beneath the Earths
  surface.
• Geysers, hot springs and venting steam such as
  Yellowstone Park are clues that this form of
  energy exists.
• The problem is getting to the geothermal energy
  (getting it to the surface) and using it in a way
  that is economically attractive.
• It is currently used to a certain extent and will
  very likely be exploited much more in the future.

58
Exercises Chapter 3

• Applying Concepts p. 81-82
• 2, 3, 4, 12, 13, 14, 15, 16, 17, 18, 19, 20
• Parallel Concepts Group A p. 82-83
• 1, 2, 3, 4, 7, 8, 9, 10, 11, 12
• New Book p. 87-89 1, 2, 3, 7, 9, 10, 11, 12,
  13, 14, 16, 18, 19, 20, 21, 22, 23, 24, 25, 26,
  27, 29, 30, 32, 34, 36.
• p. 89-90 Group A 1, 2, 3, 4, 7, 8, 9, 10, 11,
  12.

59
Review for Chapter 3

• Kinetic Energy and Potential Energy-What they are
  and the formulas.
• Relationship between Potential Energy and Work.
  Potential energy of an object is equal to its
  ability to do work.
• Formulas for Work, Energy, Potential Energy,
  Kinetic Energy
• The joule-SI unit of energy and work.
• Forms of energy mechanical, chemical, radiant,
  electrical and nuclear.
• Photosynthesis (carbon dioxide water
  energyglucose plus oxygen.)
• Burning (glucose oxygencarbon dioxide water
  energy).

• Interconversion of Energy-Any energy form can be
  converted to any other energy form.
• Flow of Energy (From the sun to plants to animals
  and humans to mechanical energy and back to the
  atmosphere).
• Conservation of Energy
• History of Energy Sources Initially wood was
  used, then coal, then petroleum.
• Energy Sources Today Chemical (Petroleumgtnatural
  gasgtcoalgtbiomass)gt
• NucleargtHydropowergtSolar.
• What is petroleum, natural gas and coal and what
  are the uses of petroleum.
• What is hydropower, solar power and nuclear
  power.
• Pollution from chemical energy and dangers from
  nuclear energy.