Intro to Physics

INTRO TO PHYSICS THERMAL ENERGY UNIT (Ch. 21.1-21.7, 22.1-22.4, 23.1-23.4, 23.8, 24.4-24.7)

I. Key Terms and Concepts

Conduction Convection Radiation Heat Temperature Temperature scales Specific Heat Capacity Thermal Energy Absolute Zero Kinetic Theory Condensation Evaporation Heat Engine Heating System Cooling System Radiant heat Heat Flow 2nd law of thermodynamics Insulators Conductors Entropy Land and sea breezes Kinetic Theory Electromagnetic radiation

II. Keys

 The total energy of the universe is constant. Energy can be transformed but never destroyed.  Heat is the manifestation of the random motion and vibrations of atoms, molecules, and ions.  The universe becomes less orderly and less organized over time (entropy).

III. Essential Questions

1. How does matter respond to changes in temperature? 2. How does the transfer of thermal energy trend toward entropy? 3. How do heating and cooling systems transfer thermal energy? IV. Learning Objectives

1. I can explain the difference between heat, temperature and thermal energy. 2. I can explain why a material will expand or contract when the temperature of the material changes. 3. I can explain how the kinetic theory helps us understand the transfer of thermal energy. 4. I can explain why heat flows and why it stops flowing. 5. I can explain the difference between a conductor and an insulator 6. I can explain why and predict in which direction a bimetallic strip will bend. 7. I can explain what the capacity of a substance to store heat depends upon. 8. I can explain the difference between a substance with a high specific heat and a low specific heat capacity. 9. I can calculate the amount of thermal energy transferred to an object, calculate the temperature change of the object and determine the composition of the material using the specific heat equation. 10.I can compare and contrast the three ways can the thermal energy of a substance be transferred, which are conduction, convection and radiation. 11.I can explain radiant energy and its source. 12.I can explain why is evaporation a cooling process and condensation a warming process 13.I can explain how thermal energy flow causes changes in phases of matter. 14.I can compare and contrast the radiant heating and forced air heating systems. 15.I can explain how air conditioners and refrigerators use evaporation and condensation to cause cooling. 16.I can model how a heat engine transfers energy. 17.I can explain entropy and how natural systems tend to proceed. 18.I can explain how land and sea breezes occur and its significance to specific heat capacity. 19.I can explain how an ocean can moderate climate. Chapters 2.2, 10.1 and 10.2 Study Guide

1. Study the summary at the end of each section. 2. Study your notes. 3. Study the answers to all homework assigned, including review homework during Week of January 5. 4. Study the key terms. 5. Study your bellwork. 6. Be able to answer the essential questions. 7. Be able to convert between different temperature scales, and to calculate energy using different specific heats. 8. Be able to convert using factor label method 9. Be able to rearrange a formula to isolate a different variable. 10. Be able to explain why the bimetallic strip bends. 11. Be able to explain the process of convection. 12. Be able to explain how heat flows when you place your finger in hot and cold water.

List of Homework Assignments Prior to Week of December 1:

Section Review 9.1; #1, #2, #5 and #7. Page 296. Section Review 9.2; #2 Handout: Simple Machine Review Sheet Page 299. Practice Problem #1 Page 301. Practice Problem #1 Page 305. Section Review 9.3; #1-#6 Page 314. Section Review 9.4; #1-#6

List of Labs

1. Measuring the Efficiency of a Ramp 2. Calculating the Mechanical Advantage of a Pulley 3. Determining the Energy of a Rolling Tennis Ball

Review Assignments

Chapter Review 1-9; 10, 12, 13, 16-18, 19, 27 Explain the major energy transformations that take place during the production of wind-source electricity, and the use of that electricity to turn electric motors such as those of the Calgary C-train:  Mechanical (wind) to Mechanical (rotation): Wind energy is simply the energy of moving air. Wind energy is a form of kinetic energy (energy of motion). When air flows over an airfoil such as on an aircraft wing or wind turbine blade, lift is generated. In the case of the airplane, the wing carries the plane aloft. In the case of the wind turbine, the airfoil is fixed to a rotating shaft at one end, which turns as lift is generated on the blades of the turbine.  Mechanical (rotation) to Electrical: Inside the wind turbine's housing is found an electrical generator that converts the energy of a spinning shaft into electricity. The spinning shaft turns a set of magnets (either permanent magnets, or electromagnets) mounted on a rotor. These magnets in turn cause an electrical current to flow in a set of tightly wound coils of wire, located close to the moving magnets.  Electrical to Mechanical (rotation): This occurs inside all electric motors, and is the reverse of what happens inside an electrical generator. In this case, an electric current is passed through coils of wire wrapped around an iron core, causing it to become an electromagnet. Several of these magnets inside the motor act on other magnets attached to a rotating shaft, which spin rapidly when a current is flowing through the coils.  Electrical to Heat: Almost all materials that are used to conduct electricity (copper wire, for instance) are not perfect conductors, and resist the flow of electricity to some degree. How much resistance there is depends on what the conductor is made of, how long the conductor is, and how large the current is. When electricity moves through a conductor with any degree of resistance, heat is always produced, which is absorbed by the air or other nearby materials. The conversion of electricity to heat is usually seen as a loss of useful energy, and steps are taken to reduce the losses, especially in long-distance transmission of electricity.  Mechanical (rotation) to Heat: In mechanical systems, moving parts are frequently in contact with non-moving parts. The result is friction, which absorbs some of the energy of motion and converts it to heat. Friction in most mechanical systems is seen as a waste of energy, and elaborate measures are taken to reduce friction. Explain that Calgary's C-train system is not powered exclusively by wind power, but that the electricity comes from a variety of sources, including coal and natural gas-fired power plants, hydroelectric stations, and others. Note that the City of Calgary has agreed to purchase enough electricity from wind energy providers (21,000 megawatt-hours of power) to supply the C-Train's needs on an annual basis.

Have students read the introduction and first chapter of The Energy Story, an online book found on the Energy Quest website; it consists of 15 brief chapters that focus on a variety of energy topics such as electricity, hydropower, and fossil fuels.

To focus student attention on the ideas in the related benchmarks, ask them to jot down notes as they read, based on the following questions:  What is "energy"?  Is there more than one kind of energy?  Can one kind of energy be changed into another? The class should then discuss their ideas about energy. Students will probably come up with several kinds of energy as examples of what energy is. Make a list of students' ideas of energy types. Some examples are listed below:  heat (warming a house, warming up liquids such as water)  mechanical work (moving things around)  electrical (lighting, cooking, lightning)  chemical (burning in engines, explosions)  light (solar cells and solar heating)  nuclear (power plants, atomic bombs) The ideas about interconversion of one form of energy into another will be implicit and explicit in student examples and discussion. In the above list, for example, we have the conversion of light energy into electrical energy in solar cells and light energy into heat energy in solar heating. Direct student attention to these conversions and get them to come up with as many as possible. Try to steer the student discussion toward the idea that all the kinds of energy they can describe and name can be converted into heat (to warm something up) and/or mechanical work (to move objects around). Work can also be converted to heat (rub your hands together briskly and feel the heat created by friction) and heat to work (in engines). We usually like to think about heat and mechanical work a bit separately, because work represents directed energy and heat is undirected. (At the molecular level, heat energy causes random molecular motion to speed up, but doesn't affect the randomness.) When students are satisfied that all the kinds of energy they know about can be converted to heat and/or mechanical work, they have as good an idea of what energy "is" as they need.

The discussion of forms of energy and their interconversion should lead to a further discussion of how energy can be measured. The objective is not to determine a numerical value for an input of energy to a system. Rather, students should be thinking about how they could tell whether a different amount of energy is input one way or another. Any kind of energy can be converted to heat energy that can be detected by warming things up. What will be warmed up and how will we know it has been warmed?

Students should discuss readily available, safe, and easy-to-handle substances to be warmed as well as how to detect the warming. Water will probably be among the substances suggested. Its advantages are accessibility and low cost, as well as ease of measurement of warming with a finger or thermometer immersed in the liquid.

Among the questions the students need to explore experimentally are:  Does it matter how much water is used?  Does it matter what temperature the water is?  Do different amounts of energy have different effects? Student teams should plan and carry out experiments to answer these and other questions they might pose for themselves.

Discussion of the results students get from the above activities should lead to conclusions such as:  The amount of water makes a difference: the more water, the smaller the amount of warming by the same amount of heat energy.  The amount of heat energy makes a difference: longer heating time with the same amount of water leads to more warming.  The initial temperature of the water probably has little effect. (Very cold or very warm water will gain or lose, respectively, heat energy from the room and this effect will be in addition to whatever heat energy source is used. Measurements with simple equipment will probably not show these effects.)