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Energy / Thermodynamics (Heat)

Energy / Thermodynamics (Heat). I. Energy: A. The ability of an object to produce change in the environment or in itself. B. Types: kinetic vs. potential (gravitational/elastic)

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Energy / Thermodynamics (Heat)

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  1. Energy / Thermodynamics (Heat) I. Energy: A. The ability of an object to produce change in the environment or in itself. B. Types: kinetic vs. potential (gravitational/elastic) C. Many forms including: thermal, light, electrical, chemical, nuclear, electromagnetic, solar, mechanical (sum of kinetic & potential) D. Energy can be transferred from one form to another. E. Energy is conserved (law of conservation) II. Work: transfer of energy through motion. (It is zero work if object doesn't move.) A. Work involves Force and Displacement (movement, change in position). B. Formula: W = F x d (work = force (wt) x displacement) C. Work units are Nm (Newton-meters) OR J (Joules)

  2. III. Simple Machines: Tools that enable (F) & (d) to be varied while keeping work constant. A. Can reduce (F) by increasing (d) through which force is exerted. B. Examples: 1. Inclined plane 5. Wedge 2. Lever 6. Screw 3. Pulley 7. Block & tackle 4. Wheel & axle IV. Friction – force opposing motion, energy used to overcome friction changes to heat. V. Power: rate at which work is done, measure of the amount of work done in a certain amount of time. A. Calculated by P = W/t B. Units are in watts (W) {1W=1 Joule/second}

  3. VI. Chemical potential energy: food A. Food is the energy (chemical PE) our bodies need to help our bodies do work (KE). B. A food Calorie (measures energy from food) is equal to 1 kilocalorie  4180 J) VII. Thermal Energy / Heat (thermodynamics) A. The transfer of energy from a higher temperature body to a lower temperature body. B. Involves: Energy transfer and Energy conservation .

  4. VIII. Molecular Kinetic Energy (KE) and Temperature (temp). A. All molecules have KE. 1. The more energy molecules absorb, the greater their KE. 2. Ex: Hot water has more KE than cold water. B. Temperature-a measure of the average KE of molecules. 1. The faster the molecules move, the higher the temp. 2. Temp. Scales – most countries use the Centigrade (Celsius) scale. a. Centigrade (Celsius)- C, water boils at 100C, water freezes at 0C b. Fahrenheit -F, water boils at 212F, water freezes at 32F c. Kelvin-(K): A thermodynamic Celsius temp. scale used to measure extreme temp. (1.) 0 Kelvin = -273C or -460F (2.) Absolute Zero or 0 Kelvin (K) – molecules have the lowest KE possible.

  5. IX. Energy Transfer-three types: A. Conduction B. Convection C. Radiation X. Energy Transfer Within a body A. Conduction: molecules transfer energy by physical (direct) contact. 1. Solid molecules easily make contact because they are close together. 2. Solids are good conductors of heat. 3. Liquids are poorer conductors of heat because molecules are farther apart. 4. Gases are the poorest heat conductors because molecules hardly ever make contact.

  6. B. Convection: molecules transfer energy by carrying it from one place to another (Ex: liquids and gases when heat rises.) 1. Gas & liquid molecules transport energy if movement is unrestricted. 2. Air is not a good conductor, but it is ideal for convection. Hot air rises by convection. 3. Convection currents-streams of hot air (ideal for gliding) or streams of warm water (in the ocean).

  7. XI. Energy Transfer Between bodies: A. Conduction between bodies: molecules in one body contact molecules in another body and transfer energy. (Ex: Hot soup to a spoon in the soup). B. Radiation: Energy transferred without direct contact. (Ex: sun’s or light rays) 1. When radiant energy is absorbed, molecules move faster & temp. rises. 2. Infrared radiation (invisible light) – all objects give off some amount of this type of radiant energy. 3. Some hot objects give off radiation in the form of visible and invisible light (Ex: hot stove-light is seen and heat is felt). C. Note: energy transfer between bodies occurs by conduction & radiation.

  8. XII. Insulators – make energy transfer difficult A. Insulation against conduction: 1. Makes molecular contact difficult. 2. A poor conductor (air) makes a good INSULATOR. 3. Examples: a. Styrofoam – pockets of air limit conduction. b. Space shuttle tiles – help shuttle withstand heat from re-entry to Earth. c. Fur / feathers trap air for insulation.

  9. B. Insulation against convection: 1. Stops molecular movement from one place to another. 2. Examples: windows, doors, weather-stripping. C. Insulation against radiation: 1. Block light rays. 2. Examples: a. Light or shiny materials reflect radiation. b. Dark or dull materials absorb radiation. c. Ozone insulates Earth from UV rays by absorbing them. D. Insulation limits transfer of energy between bodies. Ex: Wet suits limit energy transfer from a warm body to the cold water. E. Insulation limits transfer of energy within a body. Ex: Windows limit energy transfer from warm to cold air.

  10. XIII. Heat vs. Temperature A. Heat – the amount of energy transferred between 2 groups of molecules at different temperatures. B. Temperature – the measure of motion (KE) of a typical molecule within a body of matter. C. Heat Flow: 1. Heat flows from a higher temperature body to a lower temperature body. 2. Heat flows between objects in contact ONLY when a difference in temperature exists. 3. If 2 hot objects come into contact, heat will NOT flow between them IF they have the same temperature.

  11. D. Specific Heat – the amount of heat required to change a unit mass of a substance by one degree of temperature. (The amount of heat needed to change temperature by a certain amount.) 1. How difficult something is to heat or to cool. 2. A long heating time indicates a long cooling time. 3. Substances with a high specific heat are harder to heat. (Ex: water) 4. Substances with a low specific heat are easier to heat. (Ex: silver) E. Remember: Energy lost = Energy gained (Law of Conservation of Energy)

  12. XIV. Calculating Heat Energy A. Heat can be measured in calories or joules ( 1 cal = 4.18 J ). A nutritional calorie = 1 kcal = Calorie. B. Remember specific heat (heat capacity) has to do with the ability to absorb heat energy. C. Formula: Heat (J of energy gained/lost) = mass (grams) x change in temp(C) x specific heat (J/gC) H = m x T x Cp

  13. XV. Heat / Phase Change A. Phase change occurs when substances change state. B. Phase changes require energy. As more heat is added, temperature does NOT increase, instead that thermal energy goes into breaking the bonds as it changes state. (See graph at **) C. Heat of fusion: solid to a liquid. D. Heat of vaporization (liquid to a gas). E. Refer to graph.

  14. XVI. Earth Science Applications: A. Sun Energy-air/water patterns / relationships: 1. Differences between climate and weather 2. Global climate/warming, greenhouse effect • El Nino, La Nina, and other climatic trends. • Temperature effects on ground water

  15. B. Earth’s internal structure (core, mantle, crust) 1. Convection as mechanism for plate tectonics 2. Geological manifestations (plate tectonics, earthquakes, volcanoes, mountain building) 3. Impact on society C. Characteristics/Evolution of Earth in terms of age (rock sequences, fossils, relative/radiometric dating) and the geosphere, hydrosphere, atmosphere, and biosphere

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