Energy and Power


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Energy and Power

  1. 1. Energy and Power The Application of Newton’s Laws of Motion
  2. 2. Energy and Power <ul><li>POWER is the rate at which ENERGY is used </li></ul><ul><li>ENERGY is the capacity to do WORK </li></ul><ul><li>WORK = FORCE X Distance </li></ul><ul><li>FORCE = mass X ACCELERATION </li></ul><ul><li>ACCELERATION= change in VELOCITY / time elapsed </li></ul><ul><li>VELOCITY is SPEED with direction </li></ul><ul><li>SPEED = distance traveled over a period of time </li></ul>
  3. 3. Let’s Review: Describing Motion <ul><li>Speed = distance/time (m/s, km/hr, mph) </li></ul><ul><li>Velocity: Same as speed but includes direction of travel </li></ul><ul><li>Acceleration = (change in velocity)/time (m/s 2 ) </li></ul>
  4. 4. Let’s Review: Calculating Velocity and Speed <ul><li>While on vacation, Lisa traveled a total distance of 440 miles. Her trip took 8 hours. What was her average speed? </li></ul><ul><li>Speed = distance/time = 440 miles/8 hours </li></ul><ul><li>Lisa averaged a speed of 55 miles per hour </li></ul><ul><li>. </li></ul><ul><li>To determine the velocity, the direction that Lisa traveled would have to be included. </li></ul><ul><li>For example, 55 mph to the south </li></ul>
  5. 5. Let’s Review: What is Acceleration? <ul><li>Acceleration is any change in velocity ( speed and/or direction of motion) </li></ul><ul><li>Measured as rate of change of velocity </li></ul><ul><ul><li>velocity is expressed in meters per second (m/s) </li></ul></ul><ul><ul><li>acceleration is meters per second per second </li></ul></ul><ul><ul><li>expressed as m/s 2 (meters per second-squared) </li></ul></ul><ul><li>Acceleration means more than “speeding up”…… </li></ul>
  6. 6. Let’s Review: What is Acceleration? <ul><li>In physics, all of these are considered examples of acceleration </li></ul><ul><ul><li>Speeding up or slowing down </li></ul></ul><ul><ul><li>Changing direction </li></ul></ul><ul><ul><li>Changing speed and direction </li></ul></ul><ul><li>Examples of acceleration: </li></ul><ul><ul><li>A car speeding up or slowing down while traveling in a straight line </li></ul></ul><ul><ul><li>A car rounding a curve at a constant speed </li></ul></ul><ul><ul><li>A car speeding up or slowing down while rounding a curve </li></ul></ul>
  7. 7. Calculating Acceleration <ul><li>A car accelerates from 0 to 30 m/s in 5 seconds. What is its acceleration? </li></ul><ul><li>a = (30 m/s - 0 m/s)/(5 s) = 6 m/s 2 </li></ul>
  8. 8. Let’s Review: What is a Force? <ul><li>A force is a pushing/pulling agent between two objects.: </li></ul><ul><ul><li>gravity exerts a downward force on you </li></ul></ul><ul><ul><li>the seat you’re sitting in now is exerting an upward force on you (can you feel it?) </li></ul></ul><ul><li>Force is a mass times an acceleration </li></ul><ul><ul><li>mass has units of kilograms </li></ul></ul><ul><ul><li>acceleration is m/s 2 </li></ul></ul><ul><ul><li>force is then kg ·m/s 2 , or a Newton (N) </li></ul></ul>
  9. 9. Calculating Force <ul><li>A bicycle and its rider together have a mass of 80kg. If the bicycle's velocity is 6m/s, what is the force need bring it to a stop in 4 seconds? </li></ul><ul><li>Step 1: Calculate Acceleration </li></ul><ul><li>(6m/s – 0m/s) / 4sec = 1.5m/s 2 </li></ul><ul><li>Step 2: Calculate Force </li></ul><ul><li>F = ma = (80kg)(1.5m/s 2 ) = 120N </li></ul>
  10. 10. Work <ul><li>Work is the process by which energy is transferred from one object to another. </li></ul><ul><li>Work = (force)(distance) </li></ul><ul><li>W = Fd </li></ul><ul><li>Work is measure in Joules (J) in the metric system or in foot-pounds (ft-lbs) in the English system </li></ul><ul><li>The concept of work explains how we can use energy to “move things around” </li></ul>
  11. 11. Work and Energy <ul><li>Work is a force over a distance. </li></ul><ul><li>Energy is the ability to do work. </li></ul><ul><li>Machines convert energy into work. </li></ul><ul><ul><li>Example: The blender converts electrical energy into work (by moving the blade around). </li></ul></ul><ul><li>Too put it another way…… </li></ul><ul><ul><li>Energy is money in the bank </li></ul></ul><ul><ul><li>Work is when you use that money by cash, credit card, check, etc </li></ul></ul>
  12. 12. Ways of Doing Work <ul><li>Energy can do work as </li></ul><ul><li>Work against inertia </li></ul><ul><li>Work against gravity </li></ul><ul><li>Work against friction </li></ul><ul><li>Work against shape </li></ul><ul><li>Work against combinations of above </li></ul>
  13. 13. Joules <ul><li>A Joule (J) is the Standard International Unit used to compare the different forms of work or energy. </li></ul><ul><li>Conversions to other Energy Units </li></ul><ul><ul><li>1 Btu (British thermal unit) = 1055 J </li></ul></ul><ul><ul><li>1 calorie = 4.184 J </li></ul></ul><ul><ul><li>1 food calorie (Cal) = 1000 calories = 4184 J </li></ul></ul><ul><ul><li>1 kW-hr (kilowatt hour) = 3.61 x 10 6 J </li></ul></ul><ul><ul><li>1 therm = 100,000 Btu = 1.055 x 10 8 J </li></ul></ul>
  14. 14. Calculating Work <ul><li>How much work is done by pushing against a wall with a force of 100 N? </li></ul><ul><li>(100)x(0) = 0 J (wall doesn’t move) </li></ul><ul><li>How much work is done pushing a box 10 m with a 20 N force? </li></ul><ul><li>W = (20)(10) = 200 J </li></ul>
  15. 15. Two Basic Types of Energy <ul><li>Kinetic Energy (KE): the energy of motion </li></ul><ul><li>2. Potential Energy (PE): the energy of an object’s position, or STORED energy </li></ul><ul><li>The total energy of an object is equal its potential energy plus kinetic energy </li></ul>
  16. 16. <ul><li>Put the pencil at the edge of the desk and push it off to the floor. The moving pencil uses kinetic energy. </li></ul><ul><li>Now, pick up the pencil and put it back on the desk. You used your own energy to lift and move the pencil. Moving it higher than the floor adds energy to it. As it rests on the desk, the pencil has potential energy . The higher it is, the further it could fall. That means the pencil has more potential energy. </li></ul>
  17. 17. Kinetic Energy <ul><li>Kinetic Energy is the energy an object posses because of its motion. </li></ul><ul><li>Kinetic Energy depends on mass and velocity </li></ul><ul><li>K.E. = ½ mv 2 </li></ul><ul><ul><li>K.E . is kinetic energy in Joules </li></ul></ul><ul><ul><li>m is mass in kilograms </li></ul></ul><ul><ul><li>v is velocity in meters per second </li></ul></ul>
  18. 18. Calculating Kinetic Energy <ul><li>What is the kinetic energy of baseball (mass is 0.145 kg = 145 g) moving at 30 m/s (67 mph)? </li></ul><ul><ul><li>K.E. = ½  (0.145 kg)  (30 m/s) 2 </li></ul></ul><ul><ul><li>= 65.25 kg·m 2 /s 2  65 J </li></ul></ul>
  19. 19. Potential Energy <ul><li>An object does not have to be in motion to have energy. </li></ul><ul><li>Potential Energy is the energy an object has because of its position or location </li></ul><ul><li>For example, gravitational potential energy depends on mass and height of object: </li></ul><ul><li>P.E. = mgh </li></ul><ul><ul><li>P.E . is potential energy in Joules </li></ul></ul><ul><ul><li>m is mass in kilograms </li></ul></ul><ul><ul><li>g = 9.8 m/s 2 (gravitational acceleration on earth) </li></ul></ul><ul><ul><li>h is height in meters </li></ul></ul>
  20. 20. Calculating Potential Energy <ul><li>A 100 kg diver stands on a 10 meter diving board. How much potential energy does she have? </li></ul><ul><li>P.E. = (100kg)( 9.8 m/s 2 )(10m) </li></ul><ul><li>= 9800 J </li></ul>
  21. 21. Power <ul><li>Power is the rate at which work is performed or energy is transmitted over a period of time. </li></ul><ul><li>Energy is measured in Joules and time in seconds </li></ul>
  22. 22. Work vs. Power <ul><li>One way to help distinguish between work and power is to think of two people each eating an apple pie. </li></ul><ul><li>One person eats the pie faster than the other. </li></ul><ul><li>They both ate the same amount of pie (they did the same amount of work), one just ate at a faster rate (the faster one was a power eater!). </li></ul>
  23. 23. Measuring Power <ul><li>The standard metric unit of power is the Watt (W) . A Watt is equivalent to a Joule/second. </li></ul><ul><li>For historical reasons, the horsepower (hp) is used to describe the power delivered by a machine. One horsepower is equivalent to approximately 750 Watt </li></ul><ul><li>For larger quantities, watts are usually expressed in multiples of a thousand (kilowatt), million (megawatt), or billion (gigawatt). </li></ul>
  24. 24. What’s a Watt? <ul><li>A human climbing a flight of stairs is doing work at a rate of about 200 watts. </li></ul><ul><li>An average U.S. household consumes electricity at the rate of a little more than one kilowatt. </li></ul><ul><li>A typical automobile engine produces mechanical energy at a rate of 25 kilowatts (approximately 33.5 horsepower) while cruising. </li></ul><ul><li>A typical wind turbine has a one megawatt rating, and the largest are now four megawatts when turning. </li></ul><ul><li>A big coal, natural gas, or nuclear electrical plant can produce hundreds of megawatts; some of the largest generate one or more gigawatts. </li></ul>
  25. 25. Calculating Power <ul><li>How much power does it take to lift 10 kg up 2 meters in 2 seconds? </li></ul><ul><li>Step 1: Calculate Energy </li></ul><ul><li>mgh = (10 kg)  (9.8 m/s 2 )  (2 m) = 196 J </li></ul><ul><li>Step 2: Calculate Power </li></ul><ul><li>Energy/time = 200 J in 2 seconds </li></ul><ul><li>= 100 Watts </li></ul>
  26. 26. A Review of Motion Units
  27. 27. Forms of Energy <ul><li>Kinetic Energy </li></ul><ul><li>Moving energy </li></ul><ul><li>Mechanical </li></ul><ul><li>Thermal </li></ul><ul><li>Radiant </li></ul><ul><li>Electrical </li></ul><ul><li>Sound </li></ul><ul><li>Potential Energy </li></ul><ul><li>Stored energy </li></ul><ul><li>Gravitational </li></ul><ul><li>Elastic </li></ul><ul><li>Chemical </li></ul><ul><li>Nuclear </li></ul>
  28. 28. Forms of Energy Gravitational Elastic Nuclear Chemical Mechanical Thermal Radiant Sound Electrical ENERGY Kinetic Potential
  29. 29. Gravitational Energy <ul><li>Gravitational energy is due to the force of gravity caused by the attraction of all other masses to the mass of the earth. </li></ul><ul><li>As you lift an object to a higher elevation, you give that object increased gravitational energy. You can get that energy back (or most of it) when you drop the object and it falls to the earth's surface. </li></ul><ul><li>Hydropower, such as water in a reservoir behind a dam, is an example of gravitational potential energy. </li></ul>
  30. 30. Elastic Energy <ul><li>Elastic energy is contained in materials and objects that can stretch when a force is placed on them and then later return to their original shape. </li></ul><ul><ul><li>Compressed springs and stretched rubber bands are examples of stored mechanical energy. </li></ul></ul><ul><li>A spring or rubber band can be held until the it is released and the elastic energy is also released. Therefore, elastic energy is a form of potential energy. </li></ul>
  31. 31. Chemical Energy <ul><li>Chemical Energy is energy stored in the bonds of atoms and molecules. </li></ul><ul><ul><li>This energy can be retrieved when the bond is broken at a later time. </li></ul></ul><ul><ul><li>Since, for most compounds, this chemical energy can be stored in the compound for an almost indefinite time, chemical energy is a type of potential energy. </li></ul></ul><ul><li>Food and fossil fuels are examples of chemical energy </li></ul>
  32. 32. Nuclear Energy <ul><li>Energy is stored in the nucleus of an atom </li></ul><ul><ul><li>The force that holds the nucleus together is the strongest in the universe. </li></ul></ul><ul><li>The energy can be released when the nuclei are combined or split apart. </li></ul><ul><ul><li>Nuclear power plants split the nuclei of uranium atoms in a process called fission . </li></ul></ul><ul><ul><li>The sun combines the nuclei of hydrogen atoms in a process called fusion . </li></ul></ul>
  33. 33. Mechanical Energy <ul><li>Mechanical energy is energy of motion of objects that are attached together, many of which are called machines . </li></ul><ul><ul><li>These machines can be as simple as a pair of scissors or as complicated as the engine in your car. </li></ul></ul><ul><ul><li>Note that objects and substances move when a force is applied according to Newton’s Laws of Motion. </li></ul></ul><ul><li>Since the energy is energy of motion and cannot be stored, mechanical energy is a kinetic form of energy. </li></ul>
  34. 34. Thermal Energy <ul><li>Thermal Energy is the energy available in the internal motion of atoms or molecules </li></ul><ul><ul><li>All matter is made of atoms/molecules, which move around randomly </li></ul></ul><ul><ul><li>Thermal Energy increases when atomic motion increases </li></ul></ul><ul><li>Note: heat occurs when thermal energy </li></ul><ul><li>transferred from one place </li></ul><ul><li>to another </li></ul>
  35. 35. Measuring Thermal Energy <ul><li>A Btu (British thermal unit) is the amount of heat required to raise 1 pound of water by 1° Fahrenheit </li></ul><ul><ul><li>1 Btu = 1055 Joules </li></ul></ul><ul><li>A calorie (cal) is the amount of heat required to raise 1 gram of water 1° Celsius </li></ul><ul><ul><li>1 calorie = 4.184 Joules </li></ul></ul><ul><ul><li>Note: the Calories (uppercase C) in food ratings are actually kilocalories. </li></ul></ul>
  36. 36. BTU Content of Common Energy Units <ul><li>Energy consumption is expressed in BTU to allow for consumption comparisons among fuels that are measured in different units.  </li></ul><ul><ul><li>1 barrel (42 gallons) of crude oil = 5.8 X 10 6 Btu </li></ul></ul><ul><ul><li>1 gallon of gasoline = 1.24 X 10 5 Btu </li></ul></ul><ul><ul><li>1 gallon diesel fuel = 1.39 X 10 5 Btu </li></ul></ul><ul><ul><li>1 cubic foot of natural gas = 1,028 Btu </li></ul></ul><ul><ul><li>1 gallon of propane = 9.1 X 10 4 Btu </li></ul></ul><ul><ul><li>1 short ton of coal = 2.0 X 10 7 Btu </li></ul></ul>
  37. 37. Radiant Energy <ul><li>Radiant Energy is electromagnetic (EM) energy that travels in waves </li></ul><ul><li>Results from vibrations of electrons within an atom. </li></ul><ul><li>Radiant energy can be classified by the length of wave (wavelength) measured in meters (see next slide). </li></ul><ul><ul><li>The lower the wavelength, the greater the amount of energy. </li></ul></ul><ul><li>Radiant Energy is always in motion and cannot be stored, so it is type of kinetic energy. </li></ul>
  38. 38. Types of Radiant Energy Increasing Energy
  39. 39. Electrical Energy <ul><li>Electrical energy is based on the movement of electrical charges or electrons. </li></ul><ul><ul><li>Electrical charges moving through a wire is called electricity. </li></ul></ul><ul><ul><li>This flow is called current and is measured in a unit called the ampere. The more electrons that are moving the greater the current. </li></ul></ul><ul><li>Electricity must be used as soon as it is produced since as a kinetic energy it cannot be stored. Note: a battery does not store electricity, it generates electricity! </li></ul>
  40. 40. Measuring Electrical Energy <ul><li>The kilowatt-hour (kWh) is a unit of energy equivalent to one kilowatt (1 kW) of power expended for one hour (1 h) of time. </li></ul><ul><ul><li>1 kWh = 3.6 x 10 6  J = 3,412 Btu </li></ul></ul><ul><li>The kilowatt-hour is not a standard unit in any formal system, but it is commonly used to measure the consumption of electrical energy by homes and small businesses. </li></ul>
  41. 41. Sound Energy <ul><li>Movement of energy through substances in longitudinal (compression) waves. </li></ul><ul><li>Sound is produced when a force causes an object or substance to vibrate––the energy is transferred through the substance in a wave. </li></ul><ul><li>Sound Energy is always in motion and cannot be stored, so it is type of kinetic energy. </li></ul>
  42. 42. Forms of Energy Gravitational Elastic Nuclear Chemical Mechanical Thermal Radiant Sound Electrical ENERGY Kinetic Potential