1 General Science 1B Credit 4 Rev. 5/5/21 NAME:_________________________ CREDIT 4B: HEAT, WORK, AND ENERGY Learning Goal for this Credit Design an investigation or model using appropriate scientific tools, resources and methods. Lesson Title INTRODUCTION 4.1 Heat 4.2 The First Law of Thermodynamics 4.3 The Second Law of Thermodynamics PERFORMANCE TASK QUIZ Assignments   Connect to Prior Knowledge  Exploration Activity  Reading and Questions  Videos (optional)  Heat and Temperature  Review Questions  Connect to Prior Knowledge  Exploration Activity  Reading and Questions  Videos (optional)  Thermodynamics Concept Map  Review Questions  Connect to Prior Knowledge  Exploration Activity  Reading and Questions  Videos (optional)  Energy Education: Heat Engines  Review Questions   Student Support Icons Title Icon Description Review Activity This provides the students with a reminder that they need to answer questions. Technology Guides students through the tasks and assignments that require the use of technology and manipulatives. Reading This icon lets the students know they will be completing a reading activity. Credit Materials    Materials Pen/Pencil HMH Physics Textbook (optional) Packet    Technology Needs Internet Computer HMH Online Resources (optional) 2 General Science 1B Credit 4 NAME:_________________________ CREDIT 4B: INTRODUCTION Read “How Do Hot Air Balloons Fly?” and watch the video “Felix Baumgartner’s Supersonic Freefall from 128k’ – Mission Highlights” below. Then answer the essential question. How Do Hot Air Balloons Fly? What happens to an ice cube when you put it in a glass of room temperature water? As the temperature of the water decreases, the temperature of the ice increases, until both are the same temperature. The energy transferred to equalize the temperature is defined as heat. Even though the water may have cooled, the heat melted the ice cube. This energy transferred as heat can be used to do work. Work is a measure of the energy transfer that occurs when an object is moved over a distance by an external force. For example, look at the picture of a hot air balloon to the right. The balloon is filled with hot air so that the air inside the balloon has a higher temperature than the air outside of the balloon. The difference in temperature causes energy transfers between the gas inside of the balloon and the air outside. This transfer of energy as heat is used to do work by lifting the balloon, causing it to rise into the air! An essential question is something that allows you to explore what the credit is about. Before you answer the question, examine the picture. Watch the video if you feel you need more information. Then, answer the essential question to the best of your ability. You will revisit it at the end of the credit to see if your answer has evolved. Felix Baumgartner’s Supersonic Freefall from 128k’ – Mission Highlights (1:30) https://www.youtube.com/watch?v=FHtvDA0W34I “Felix Baumgartner’s Supersonic Freefall from 128k’ – Mission Highlights.” YouTube. Red Bull, 4 Oct. 2012. Web. 26 Jan. 2016. Essential Question If a balloon uses heat as energy to rise, how do you think it is able to come back down to the ground? Where does the energy go? __________________________________________________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ 3 General Science 1B Credit 4 LESSON 4.1: HEAT Learning Goal for this Credit Design an investigation or model using appropriate scientific tools, resources and methods. Learning Goals for this Lesson  Relate temperature to the kinetic energy of atoms and molecules.  Describe the changes in the temperatures of two objects reaching thermal equilibrium.  Identify the three temperature scales and convert from one scale to another.  Explain heat as the energy transferred between substances that are at different temperatures. Lesson Assignments  Connect to Prior Knowledge  Exploration Activity  Reading and Questions  Videos (optional)  Animated Physics: Heat  Review Questions Engage Connect to Prior Knowledge What are some ways in which the temperature of a substance can be measured? _________________________________________________________________________________________ _________________________________________________________________________________________ _________________________________________________________________________________________ _________________________________________________________________________________________ 4 General Science 1B Credit 4 Explore Exploration Activity The outdoor temperature range from region to region can vary greatly. In Death Valley, California temperatures can regularly reach 120 degrees Fahrenheit (o F) during the summer. The unit most used in the United States to measure temperature is the Fahrenheit (o F) scale. In other countries the Celsius (o C) scale is used to measure temperature. In Antarctica, over the elevated inland, temperatures can drop below -80 degrees Celsius (o C) during the winter. Even though there are different units used to measure temperature, these units of Fahrenheit and Celsius can be converted to each other using the following equation. 𝟗 𝑻𝑭 = 𝑻𝑪 + 𝟑𝟐. 𝟎 𝟓 TF = Temperature in degrees Fahrenheit TC = Temperature in degrees Celsius Formula for converting F and C In this equation TF represents the temperature in degrees Fahrenheit (o F) and TC represents the temperature in degrees Celsius (o C). The 32.0 represents the difference on each scale where water freezes. On the Celsius scale water freezes at 0.0 degrees and on the Fahrenheit scale water freezes at 32.0 degrees. Example: The average human body temperature is 37oC. What is the equivalent temperature on the Fahrenheit scale? Step 1: Write out the equation where x represents the unknown temperature we are trying to find. In this problem we know the temperature in oC and the unknown is the temperature in oF. 𝟗 𝒙 = ( ) × (𝟑𝟕) + 𝟑𝟐 𝟓 Step 2: Using order of operation, begin solving for x. First divide the fraction in the parenthesis. 𝒙 = (𝟏. 𝟖) × (𝟑𝟕) + 𝟑𝟐 Step 3: Then multiply. 𝒙 = 𝟔𝟔. 𝟔 + 𝟑𝟐 Step 4: Then add. 𝒙 = 𝟗𝟖. 𝟔 The average body temperature in degrees Fahrenheit equals 98.6 oF. 5 General Science 1B Credit 4 Another unit that is used to measure temperature is Kelvin (K). A temperature difference of one degree is the same on the Kelvin and the Celsius scales. The two scales only differ in the choice of the zero point. On the Kelvin scale, absolute zero is 0oKelvin, and is the temperature that is the lowest possible. On the Celsius scale absolute zero is represented by the temperature -273.15oC. The equation below is used to convert between the units Celsius and Kelvin. 𝑻 = 𝑻𝑪 + 𝟐𝟕𝟑. 𝟏𝟓 T = Temperature in degrees Kelvin TC = Temperature in degrees Celsius Formula for converting K and C In this equation T represents temperature in Kelvin and TC represents the temperature in degrees Celsius (oC). The 273.15 represents the difference in the zero point. Example: Water boils at approximately 100oC. What is the boiling point of water on the Kelvin Scale? Step 1: Write out the equation where x represents the unknown temperature we are trying to find. In this problem we know the temperature in oC and the unknown is the temperature in K. 𝒙 = 𝟏𝟎𝟎 + 𝟐𝟕𝟑. 𝟏𝟓 Step 2: Using addition, solve for x. 𝒙 = 𝟑𝟕𝟑. 𝟏𝟓 The boiling point of water on the Kelvin scale is equal to 373.15 K. Using the equations and examples, answer the following questions. Make sure to show your work. 1. On the Fahrenheit scale, water freezes at 32oF. a. What is the equivalent temperature on the Celsius scale? b. Now that you know the temperature equivalent on the Celsius scale, what is the equivalent on the Kelvin scale? 6 General Science 1B Credit 4 2. Dry ice, which is the solid form of carbon dioxide (CO2), has a very low temperature of -78.5oC. a. What is the temperature of dry ice expressed on the Kelvin scale? b. What is the temperature of dry ice expressed on the Fahrenheit scale? 3. The lowest temperature ever recorded on Earth is -128.6oF, recorded in Antarctica in 1983. a. What is this temperature on the Celsius scale? b. Now that you know the temperature on the Celsius scale, what is the equivalent on the Kelvin scale? 7 General Science 1B Credit 4 Explain As you complete the reading, answer the questions in the space provided. Reading What is Heat? Temperature is the quantity that tells us how hot or cold a substance is. Temperature can be measured on a thermometer using either the Fahrenheit, Celsius, or Kelvin scales. Temperature is the measure of the average kinetic energy of the particles in a substance. Recall that kinetic energy is the energy of motion. When a substances temperature rises, the molecules move faster, increasing the substances kinetic energy. When you touch a hot pan on the stove, energy is transferred to your hand from the pan because the pan is hotter than your hand. If you touch a piece of ice, energy will enter the ice from your hand because the ice is colder than your hand. The direction of energy transfer is always from hotter to colder. This energy transfer that takes place because of temperature differences is known as heat. Matter contains energy in various forms, but does not contain heat. Heat is energy moving from a hotter substance to a colder substance. Once heat is transferred, and the substances in contact with each other reach the same temperature, we say the objects are in thermal equilibrium. At this point the energy ceases to be heat. For example, when ice is added to a hot cup of water, energy in the form of heat transfers from hot water to the ice. The water decreases in temperature as it loses energy, and the ice increases in temperature as it gains energy. Once the ice is melted and the ice/water mixture has a stable temperature, it has reached thermal equilibrium. 1. Why is it incorrect to say matter contains heat? _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 2. What is thermal equilibrium? _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ How is Heat Transferred? Heat can be transferred by conduction, convection, and radiation. If you walk on a cold tile floor barefoot you will feel the cold on your warm feet. Heat is transferring through your feet to the tile floor by conduction. Conduction of heat takes place when energy is transferred from one substance to another when the substances are in direct contact. In electricity, the flow of a charge through a wire is also an example of conduction. On a cold day, a fireplace may be used to warm the air in our homes. This warm air travels upward to displace the cooler air in the room. This movement of heat through the air is known as convection. Convection can take place in a gas or a liquid. Whether we heat water in a pot or heat the air in a room, the process is the same. 8 General Science 1B Credit 4 Recall that convection currents take place within Earth’s interior causing the movement of Earth’s tectonic plates. Heat from the sun warms Earth’s surface. It passes through space and Earth’s atmosphere in the form of radiant energy. This is an example of radiation. Radiation is the transfer of energy by electromagnetic waves. Electromagnetic waves include radio waves, microwaves, infrared, visible light, ultraviolet light, x-rays, and gamma rays. When a fireplace is heating a room, the majority of the heat goes up the chimney by convection, but that heat that warms a person sitting near the fire comes to them by radiation, mainly from infrared waves. Conduction Convection Radiation 3. How does conduction occur? _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 4. How is a fireplace an example of both convection and radiation? _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 5. Give one example for each form of heat transfer (conduction, convection, radiation). _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ Adapted from Hewitt, Paul G. “Chapter 21: Temperature, Heat, and Expansion/Chapter 22: Heat Transfer.” Conceptual Physics: the High School Physics Program, Pearson/Prentice Hall, 2006, pp. 307–336. 9 General Science 1B Credit 4 Videos If you would like to learn more about this topic, watch the videos below for more information. (Optional) Thermal Equilibrium (3:47) https://www.youtube.com/watch?v=gzy4YFuKg9A “Thermal Equlibrium” YouTube. Bozeman Science, 26 Jul. 2015. Web. 29 Apr. 2021. How does heat move between two objects of different temperatures? This video will explain how thermal equilibrium is obtained within a system. Converting Between Temperature Scales (6:17) https://www.youtube.com/watch?v=4cM0ollAhKM “Converting Between Temperature Scales (Celsius, Fahrenheit, and Kelvin)” YouTube. Professor Dave Explains, 3 Jul. 2017. Web. 29 Apr. 2021. How is temperature converted between the different units of Celsius, Fahrenheit, and Kelvin? This video will explain the temperature conversion process. Misconceptions About Temperature (3:59) https://www.youtube.com/watch?v=vqDbMEdLiCs&t=20s “Misconceptions About Temperature.” YouTube. Veritasium, 24 Aug. 2012. Web. 15 Feb. 2016. When you touch something do you feel its temperature? This video will explain how heat transfer and conductivity are related to perceived temperature. 10 General Science 1B Credit 4 Elaborate Heat and Temperature The following video examines what heat is at a molecular level. Follow the link below to watch it, then answer the questions. Heat and Temperature https://www.youtube.com/watch?v=LL54E5CzQ-A “Heat and Temperature.” YouTube, Professor Dave Explains, 23 Mar. 2017. 1. What is heat? _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 2. How is the mass and speed of a particle related to its kinetic energy? _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 3. How is kinetic energy related to temperature? _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 4. How are temperature and heat related? _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 11 General Science 1B Credit 4 Evaluate Review Questions Answer the following questions. 1. In what direction does heat flow between two objects of different temperatures? _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 2. If you leave a cup of hot chocolate sitting on a table what eventually happens to the temperature? Does the temperature ever reach a thermal equilibrium? _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 3. In what three ways can energy be transferred as heat? _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 4. Ultraviolet light is the cause of sunburns. What type of heat transfer has occurred when a person gets a sunburn from ultraviolet light? _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 12 General Science 1B Credit 4 LESSON 4.2: THE FIRST LAW OF THERMODYNAMICS Learning Goal for this Credit Design an investigation or model using appropriate scientific tools, resources and methods. Learning Goals for this Lesson  Illustrate how the first law of thermodynamics is a statement of energy conservation.  Describe absolute zero and how it relates to the internal energy of a system.  Explain changes in heat, work, and internal energy by applying the first law of thermodynamics. Lesson Assignments  Connect to Prior Knowledge  Exploration Activity  Reading and Questions  Videos (optional)  Thermodynamics Concept Map  Review Questions Engage Connect to Prior Knowledge Give an example in which energy as heat is used to perform a task. _________________________________________________________________________________________ _________________________________________________________________________________________ _________________________________________________________________________________________ _________________________________________________________________________________________ 13 General Science 1B Credit 4 Explore Exploration Activity Thermodynamics is the study of heat and its transformation to energy. Recall that heat is a form of energy transfer between substances of different temperatures, and energy is a property of an object or system that enables it to do work. When heat is added to a system, it transforms to an equal amount of some other form of energy. A system is a portion of the physical universe chosen for analysis. Everything outside of the system is known as the environment. The first law of thermodynamics states that energy can neither be created nor destroyed. It can only change forms. In any process, total energy remains the same. For thermodynamic systems, the heat supplied to the system can be used to do work. The internal energy of a system can be changed by transferring energy from the environment into or out of the system as work, heat, or both. 1. Rub your hands together as quickly as you can. What did you observe? _______________________________________________________________________________________ _______________________________________________________________________________________ 2. The work you did on your skin is converted to thermal energy. Rub your hands together again. Now place them on your face. What do you feel on your face? _______________________________________________________________________________________ _______________________________________________________________________________________ 3. The thermal energy is transferred from your hands to your face in the form of heat. Work and heat are interchangeable. What might be an example where you add heat to something to do work? (Hint: reread the Introduction on page 3 of this credit) _______________________________________________________________________________________ _______________________________________________________________________________________ 14 General Science 1B Credit 4 Explain As you complete the reading, answer the questions in the space provided. Reading What is Absolute Zero? As the motion of atoms in a substance increases, temperature also increases. In contrast, as motion of atoms in a substance decreases, temperature will decrease. As the motion of these atoms approaches zero, the temperature of the substance approaches its lower limit. The lower limit of temperature is known as absolute zero. At absolute zero, no further lowering of a substances temperature can occur, and no more energy can be extracted from the substance. Absolute zero corresponds to zero degrees on the Kelvin scale or -273 degrees on the Celsius scale. 1. Can the temperature of a substance go below absolute zero? Explain your answer. _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ What is the First Law of Thermodynamics? The first law of thermodynamics states that energy can neither be created nor destroyed. It can only change forms. When this is applied to thermodynamic systems, it means that whenever heat is added to a system it transforms to an equal amount of another form of energy. A system can be as small as a group of atoms, or as large as the universe. A car engine, planet Earth, or even your body can be considered a system. If we add energy to a system in the form of heat it can do one or both of two things:   Increase the internal energy of the system if it remains in the system. Do work on the environment if it leaves the system. So, the first law of thermodynamics can be summed up as: Heat added = Increase in internal energy + External work done by the system For example, as heat is added to a hot air balloon, it does work causing the balloon to rise into the air. The balloon is a thermodynamic system. The added heat increases the internal energy, causing the air inside the system to be hotter than the air of the surrounding environment. Work is done as the balloon rises. If the heat is no longer added to the balloon, eventually the air temperature inside of the balloon with lower back down to the temperature of the air in the surrounding environment to achieve thermal equilibrium. Work will no longer be done, and the balloon will descend to the ground. 15 General Science 1B Credit 4 2. Explain the first law of thermodynamics. _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 3. If energy is added to a system in the form of heat, what two things can occur? _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 4. What is an example of a system? What would be the external environment for this system? _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ Adapted from Hewitt, Paul G. Conceptual Physics. Upper Saddle River, NJ: Prentice Hall, 2006. Print. Videos If you would like to learn more about this topic, watch the videos below for more information. (Optional) What is Absolute Zero Temperature? (2:27) https://www.youtube.com/watch?v=QTYlC70VV_I “What Is Absolute Zero Temperature.” YouTube, Pocket Science, 7 Nov. 2014. What is absolute zero? This video explains how cold absolute zero actually is and the temperature readings of absolute zero on the Kelvin and Celsius scales. What is the First Law of Thermodynamics? (4:08) https://www.youtube.com/watch?v=1OFlW8OXN64 TheRoyalInstitution. “What Is the First Law of Thermodynamics?” YouTube, YouTube, 5 Dec. 2016. What is the first law of thermodynamics? This video will explain the first law of thermodynamics as well as how heat can be used to do work. 16 General Science 1B Credit 4 Elaborate Thermodynamics Concept Map Complete the concept map below to explain the first law of thermodynamics. Each term can be found in the reading section from this lesson. Work System Energy Heat Environment Thermodynamics Internal Energy Serway, Raymond A., and Jerry S. Faughn. “Chapter 10: Thermodynamics/Concept Map: Thermodynamics.” Holt McDougal Physics, Holt McDougal, a Division of Houghton Mifflin Harcourt Publishing Co., 2012. Evaluate Review Questions Answer the following questions. 1. What is the lowest possible temperature on the Celsius scale? On the Kelvin scale? _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 2. If heat is added to a system, what happens to the internal energy? _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 3. If external work is done on the environment by a system, what happens to the internal energy? _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 17 General Science 1B Credit 4 LESSON 4.3: THE SECOND LAW OF THERMODYNAMICS Learning Goal for this Credit Design an investigation or model using appropriate scientific tools, resources and methods. Learning Goals for this Lesson  Recognize why the second law of thermodynamics requires two bodies at different temperatures for work to be done.  Relate the disorder of a system to its ability to do work or transfer energy as heat. Lesson Assignments  Connect to Prior Knowledge  Exploration Activity  Reading and Questions  Videos (optional)  Energy Education: Heat Engines  Review Questions Engage Connect to Prior Knowledge Give an example of a process where heat flows from a warmer object to a colder object. _________________________________________________________________________________________ _________________________________________________________________________________________ _________________________________________________________________________________________ _________________________________________________________________________________________ 18 General Science 1B Credit 4 Explore Exploration Activity It is easy to change work completely into heat. You did this in the last lesson by rubbing your hands together. The reverse process of changing heat completely into work is something that cannot be done. Some heat can be converted to work, but the rest is always lost. A heat engine is a device that converts internal energy into work. Internal energy is increased by the addition of heat. The first heat engine, the steam engine, was invented in the 1700s. Today, a type of steam engine called a steam turbine is used to produce most of the electricity for the United States. In the example to the right, water is heated in a high-pressure boiler. The water evaporates and becomes steam. The steam travels through a chamber to a turbine. The turbine spins when the highly pressurized steam pushes the blades. The turbine is connected to an external generator that collects mechanical energy as electricity. The steam is cooled once it passes through the turbine and becomes water again. A pump takes the water back up to the boiler to start the process over. In this steam turbine heat is used to do mechanical work, but not all of the heat gets converted to work. Some is lost to friction and the outside environment. Recall that friction is a force that resists motion of objects that are in contact with each other. 1. What is a heat engine? _______________________________________________________________________________________ _______________________________________________________________________________________ 2. What are steam turbines used to produce? _______________________________________________________________________________________ _______________________________________________________________________________________ 3. Some of the heat of the steam turbine is converted into mechanical work. What happens to the rest of the heat that is not converted to work? _______________________________________________________________________________________ _______________________________________________________________________________________ Adapted from Hewitt, Paul G. “Chapter 24: Thermodynamics/Section 24.5: Heat Engines and the Second Law”. Conceptual Physics: the High School Physics Program, Pearson/Prentice Hall, 2006, pp. 361-362. 19 General Science 1B Credit 4 Explain As you complete the reading, answer the questions in the space provided. Reading What is the Second Law of Thermodynamics? The second law of thermodynamics states that heat will never of itself flow from a colder object to a hotter object. This means that the direction of heat flow is from hot to cold unless work is added to the system. Heat can be made to flow the other way, but only by adding work from an external source. For example, a refrigerator’s electric motor acts as an external source to reverse heat flow and keep your food cold. It is easy to change work completely into heat; simply rub your hands together or push a crate at constant speed across a floor. The work you do in overcoming friction is completely converted to heat, but the reverse process of changing heat entirely to work cannot occur. The second law of thermodynamics also explains that no cyclic process that converts heat entirely to work is possible. The best than can be done is the conversion of some heat to mechanical work. This process is what powers gasoline driven automobiles. A heat engine is a device that changes internal energy into mechanical work. The basic idea behind a heat engine is that mechanical work can be obtained only when heat flows from a high temperature to a low temperature. In every heat engine only some of the heat can be transformed into work. No heat engine can transfer all its absorbed energy to work. The measure of how well a heat engine operates is called the engine’s efficiency. Efficiency measures the useful energy taken out of a process relative to the total energy put into a process. The higher the percentage, the more efficient the heat engine. 1. Explain the second law of thermodynamics. _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 2. What is a heat engine? _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 20 General Science 1B Credit 4 3. What is efficiency a measure of for a heat engine? _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ What is Entropy? Recall that the first law of thermodynamics states that energy can be neither created nor destroyed, it can only change forms. The second law of thermodynamics adds that heat transfers from hot to cold substances. Work can be done by this heat flow which causes an increase of internal energy, but not all the heat can be converted to work. The wasted heat is unavailable or lost. Another way to say this is that some of the available (ordered energy) becomes unavailable (disordered energy). The idea of ordered energy tending to disordered energy is the concept of entropy. Entropy is a measure of disorder within a system. In natural systems, over time, entropy always increases and the available energy of the system for doing work decreases. However, if work is added to the system, it can decrease the entropy. For example, all living organisms input work to decrease entropy. They take in energy from the surrounding environment and use it to do work inside their bodies to decrease disorder. This energy transformation is what supports life. But as with all living organisms, eventually this energy intake and transformation slows, and then stops. The organism soon dies and tends to disorder as it decomposes. 4. What is entropy a measure of? _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 5. How would entropy relate to the efficiency of a heat engine? _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ Adapted from Hewitt, Paul G. Conceptual Physics. Upper Saddle River, NJ: Prentice Hall, 2006. Print. 21 General Science 1B Credit 4 Videos If you would like to learn more about this topic, watch the videos below for more information. (Optional) What is Entropy (5:19) https://www.youtube.com/watch?v=YM-uykVfq_E “What is entropy?.” YouTube. TED-Ed, 9 May. 2017. Web. 29 Apr 2021. What is entropy? This video will explain entropy and give examples of entropy found in everyday objects. The Rubber Band Heat Engine (5:46) http://www.youtube.com/watch?v=dBXL93984cQ “The Rubber Band Heat Engine.” YouTube. Adam Micolich, 5 Sept. 2008. Web. 04 June 2014. How can a rubber band be used to create a heat engine? This video will show you how even a simple heat engine can be used to do work. 22 General Science 1B Credit 4 Elaborate Energy Education: Heat Engines Read the following information on heat engines and then answer the questions. Heat Engine A heat engine is a device (like the motor in a car) that produces motion from heat. When people rub their hands together friction turns mechanical energy (the motion of our hands) into thermal energy (the hands get warmer). Heat engines do just the opposite; they take the energy from being warm (compared to the surroundings) and turn that into motion. Often this motion is turned into electricity with a generator. Almost all of the energy that is harnessed for transportation and electricity comes from heat engines. Hot objects, even gases, have thermal energy that can be turned into something useful. Heat engines move energy from a hot place to a cold place and divert some of that energy into mechanical energy. Heat engines require a difference in temperature to function. The study of thermodynamics was initially inspired by trying to get as much energy out of heat engines as possible. To this day, various fuels are used, like gasoline, coal, and uranium. All of these heat engines still operate under the limits imposed by the second law of thermodynamics. This means that various fuels are used to heat a gas and a large cold reservoir is needed in order to get rid of waste heat. Often, the waste heat goes into the atmosphere or a large body of water (the ocean, a lake, or a river). Depending on the type of engine, different processes are employed, like igniting fuel through combustion (gasoline and coal), or using energy from nuclear processes to produce heat (uranium), but the end goal is the same: to turn the heat into work. The most familiar example of a heat engine is the engine of a car, but most power plants, like coal, natural gas, and nuclear, are also heat engines. Internal Combustion Engine Internal combustion engines are the most common form of heat engines, as they are used in vehicles, boats, ships, airplanes, and trains. They are named as such because the fuel is ignited in order to do work inside the engine. The same fuel and air mixture is then emitted as exhaust. While this is most commonly done using a piston, it can also be done with a turbine. The picture below is an example of an internal combustion engine. This particular type is called a four stroke engine, which is quite common in cars. External Heat Engine External heat engines are generally steam engines, and they differ from internal ones in that the heat source is separate 23 General Science 1B Credit 4 from the gas that does work. These heat engines are usually called external combustion engines because combustion is occurring outside of the engine. For example, external combustion would be using a flame to heat water into steam, then using the steam to turn a turbine. This is different from internal combustion, like in a car engine, where the gasoline ignites inside a piston, does work, and then is expelled. Nuclear reactors don’t have combustion, so the broader term external heat engine is used. The boiling water reactor is an external heat engine, as are other nuclear power plants. Cogeneration A heat engine has two byproducts: work and heat. The purpose of most engines is to produce work, and the heat is treated simply as waste. Cogeneration is using the waste heat for useful things. The heater in a car works using cogeneration – taking waste heat from the engine to heat air which warms up the cabin. This is why running a car’s heater in winter has little effect on gas mileage, but running air conditioning in the summertime can cost an estimated 10-20% of a car’s gas mileage. 1. What are some of the types of fuels that are used in heat engines? _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 2. Where is the “waste heat” generally disposed of from a heat engine? _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 24 General Science 1B Credit 4 3. What type of things are internal combustion heat engines used in? _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 4. How does an external heat engine differ from an internal heat engine? _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 5. Nuclear reactors do not have combustion, so how is heat supplied to do work? _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 6. Explain cogeneration. _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ Campbell, Allison, Fatima Garcia, Jordan Hanania, James Jenden, and Jason Donev. “Heat Engine.” – Energy Education. University of Calgary, n.d. Web. 18 Feb. 2016. 25 General Science 1B Credit 4 Evaluate Review Questions Answer the following questions. 1. How does the second law of thermodynamics relate to the direction of heat flow? _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 2. Would a heat engine be more efficient in an environment that generally has warm or cold temperatures? Explain your answer. _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 3. What must be added to a system to decrease entropy? _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ Revisit the essential question. Did your answer change? Why or why not? Essential Question If a balloon uses heat as energy to rise, how do you think it is able to come back down to the ground? Where does the energy go? __________________________________________________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ 26 General Science 1B Credit 4
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