Energy and the Environment

Transcription

1 Energy and the Environment Energy physics definition the capacity to do work and conjunction used to connect grammatically coordinate words, phrases, or clauses the Environment the aggregate of surrounding things, conditions, or influences; surroundings; milieu; the air, water, minerals, organisms, and all other external factors surrounding and affecting a given organism at any time.

2 So what is work? The work done on an object is the product of an applied force and how far the object moves under the action of the force. Or Work = Force times displacement In symbols W = F d Work transfers energy from one place to another or from one form to another.

3 That was important Work and energy are usually one and the same. The work done usually on an object usually shows up as energy gained by the object. Work transfers energy from one place to another or from one form to another. What does this mean fundamentally? Energy is a conserved quantity meaning that it cannot be created or destroyed but can be transformed from one type to another or moved from one place to another.

4 So now what is a force? A force we ll tacitly define as any push or pull. Thus to apply a force we have to interact with the object and for work to be done the object has to move!! Problems: What are the units of force, displacement, work and energy? How do we convert back and forth between different units? Why are there so many units?

5 Units and Conversions: Quantity English System Metric System Force pound (lb) Newton (N) Displacement foot (ft) meter (m) Work & Energy foot-pound (ft-lb) Joule (1 J = 1 Nm) Conversions: 1 m ~ 3 feet 1 N ~ ¼ pound

6 A quick calculation: Suppose that you push a box along a floor by applying a force of 100 N and you move the box through a distance of 10m. How much work was done? In Metric Units W = F d = 100 N 10m = 1000Nm = 1000J Or in English Units W 1 4 lb 3 ft = F d = 100N 10m 750 1N 1m Another conversion: ft lb = 1000J 1ft lb J 1. 33J 750 ft lb

7 Comments: 1. We are going to run into many energy units and we ll need to be able to convert back and forth between them. Energy Conversion Factors. We are also going to run into extremely large or small numbers and we want a convenient way to write these numbers. Scientific Notation 3. There are other ways to express energies in terms of the rate at which work is done. Power J kw. hr Btu 1 J 1.78x x kw. hr 3.6x cal x x Btu x ft. lb x x ev 1.6x x x10 -

8 Forms of Energy Chemical energy stored in chemicals or materials that is released, usually as heat, through a reaction such as usually combustion. Thermal (heat) energy associated with the random motion of the atoms or molecules that make up a substance. Q = weight T Nuclear (mass) energy associated with the conversion, or loss, of mass in 8 m 5 a nuclear reaction. E = mc ; c = 3 10 = s mi s Kinetic mechanical energy associated with the motion of mass. KE = 1 mv Potential energy associated with an arrangement of objects. PE = mgh Electric energy associated with moving electric charges. Electromagnetic energy associated with various forms of light such as radio waves, TV, microwaves, thermal, visible light, ultraviolet, and x-rays.

9 Comments: PE is relative and only differences in PE are important. Energy Units there are so many and they seem very random. British Thermal Unit (Btu) the Calorie (cal) heat energy needed to raise the temperature of 1 pound of water by 1 o Fahrenheit. like the Btu it is the amount of energy needed to raise the temperature of 1 gram of water by 1 o Celsius. The Calorie (Cal) usually in reference to food is about 1000 times larger than the cal. Kilowatt-hour an energy unit that your local electric company delivers (and bills for) energy.

10 Mass Mass is usually measured in kilograms (metric units) or slugs (English units) and represents the amount of stuff in an object. A kilogram of mass corresponds to a weight of about. pounds. Mass and weight are not the same. Weight is a force and is related to mass by a common factor called the acceleration due to gravity. Weight W mass = = = m g 9.8 ( = acceleration) ( in N ) W ( in lbs) s 3. s ft Mass in kg 1 slug = 14.6 kg Mass in slugs

11 Kinetic and Potential Energy Calculations A car and driver with a combined mass 000-lbs are moving down a straight level road at a speed of 30-mph (~ 13 m/s). How much mass does the car and driver have in kg and how much KE does the car and driver possess? 1kg m = 000lb = 909kg.lb KE = m 4 ( 13 ) = 7.7 J 1 1 mv = 909kg 10 Suppose that I drive this car up a hill starting with the amount of KE above and that the hill is 6 m (~ 18 feet) above ground level. If I park the car at the top of the hill, how much potential energy is stored in this system and what happened to my initial KE? Is energy conserved? PE = mgh = 909kg 9.8 6m = s m 4 s The KE was transformed to PE and some was dissipated as heat (due to friction between the tires and road). J

12 A Nuclear Energy Calculation How much energy would be released if a 1 pound mass were to be converted entirely to energy? E = mc = 8 m 16 ( 3 10 ) = J 1kg 1 lb s.lb Comment: A 3-g stick of dynamite (a true M-80 firecracker) releases an energy of about of 1.3x10 4 J. The energy in a firecracker is not released in the same manner as in a nuclear process. In a nuclear process we convert mass to energy while in a firecracker we convert flash powder to chemical energy, sound, and light. The energy contained in a 1 pound mass corresponds to many firecrackers. (3.x10 1 or 3. trillion as a matter of fact!) There is a lot of energy released when a nucleus is broken apart!

13 Power A useful quantity is the rate at which work is done or energy is produced/released. This is called power. Power = Energy time The units, for example, are Btu s per hour or Joules per second (the Watt). Some processes may contain the same amount of energy but the power depends on how fast or slow that energy is released. A 100-g jelly donut contains about 1.6x10 6 J of energy while our 3-g firecracker has 1.3x10 4 J. This jelly donut contains more energy (per amount of mass), but is released over a longer period of time and has a very low power. A firecracker releases its energy very quickly, is very powerful, and that s why you don t want to stand very close.

14 So what is this course? Energy and the Environment is the study of energy in all of its forms, through the work done on (or maybe by) the environment by some external agent and the connections between the different energies and the impact theses energies have on the surroundings. In addition we ll study production, control, sustainability of different energy sources and their relation to the environment.

15 Solutions to Selected Problems Q & 4 Climbed a flight of stairs and converted KE at the bottom of the stairs to PE and KE at the top. Work was done converting chemical energy in my body to mechanical energy (me walking) and to PE. Picked up a book and put it on a shelf. Stored PE in the book by me doing work to pick the book up. The energy stored in the book came from chemical energy in my body. Q 5 & 4 The ball had some KE (and PE depending on where you define the reference for potential energy) just after being released. At the top of its motion the ball had transformed all of its initial KE (and PE) into all PE at the highest point in its motion. On the return trip back down, all of the PE that was stored is converted continuously back into (PE and) KE just before the ball is caught. The energy contained in the ball went into my hand and was turned into sound (I heard it hit) and pain (electrical energy.) (Maybe some was converted to heat also.)

16 Solutions to Selected Problems MC 1 ( 5 ) ( 6 ) ( 7 ) ( ) ( ) 18 0 F : = = =.1 10 MC m 5 ( 30 ) = 900,000J = 9 J 1 G : KE = 1 mv = 000kg 10 MC 4 8 Btu 1yr 1055J D : = 10,98W 11,000W = 11kW 6 yr s 1Btu s MC 11 B : MC 1 E = mc 1kg = 1lb.lb kg m 8 m s 16 ( 3 10 ) = = J s W 3600s B : E = P t = 1hp 1hr = 1hp 1hr = hp 1hr J

17 Where does our energy in the United States come from? 86% fossil fuels (coal, natural gas, and oil) 14% hydroelectric, nuclear, wind, geothermal and solar. Should we be concerned about our energy use? 1. Yes perhaps because fossil fuels are limited in amount. -Where did they come from? -How long did they take to make? -Are they still being produced? -About how long have we been using fossil fuels? -How long before we cannot extract any more of these fuels? -Coal? -Natural gas and oil?

18 Should we be concerned about our energy use?. Yes perhaps because of the environmental consequences of using fossil fuels on such an extensive basis. -Problem(s)? -Solution(s)? Why do we use so much energy? -We are inefficient in our use of resources. -We enjoy our standard of living. -Industrialized Society vs. Non-industrialized societies? -Cell phone, IPod, computer, coffee pot, TV, car, airplane flights, fun parks, going out to dinner, going to the grocery store, heat in the winter & cool in the summer,.. What if we didn t know about fossil fuels what would life be like? Would we have put more time and effort into labor easing technologies involving wind, water, wood, nuclear, solar?

19 Renewable and Non-Renewable Energy Sources What s the difference? What are the types of renewable and non-renewable energies? Are there well defined definitions that allow different energies to be placed in each category? Could a type of energy be in both categories? Renewable Non-Renewable Solar and sunlight Coal, oil, natural gas ** Wind (due to sunlight and motion of earth) Hydroelectric power 35 U nuclear fission fuel H nuclear fusion fuel Geothermal ocean currents and temp. gradients Wood

20 So where do we go from here? On to examine different energies and their impact on the environment in greater detail!

21 Assignment # Read chapter 1 pages 15 7 Q 1, 6, 9, 11 MC 5, 9 Due on Monday, January 14, 008