Presentation on theme: "Upcoming Classes Tuesday, Oct. 9 th Dissecting the iPod Assignment due: * Homework #4 (Egg container) Thursday, Oct. 11 th Design at the Nexus Assignment."— Presentation transcript:
Upcoming Classes Tuesday, Oct. 9 th Dissecting the iPod Assignment due: * Homework #4 (Egg container) Thursday, Oct. 11 th Design at the Nexus Assignment due: * Topic and outline for second paper or oral presentation
Upcoming Deadlines Thursday, October 11 th Outline of second oral presentation or written paper Tuesday, November 6 th Second Set of Oral Presentations Second term paper (if not presenting)
Oral Presentations (II) The following persons will give oral presentations on Tuesday, November 6 th : Luttrell,Katherine Macdonald,Keith McDonald,Kathleen Mendoza,Jazmin Nguyen,Jennifer Nguyen,Linda For everyone else, term paper is due on that date.
Extra Credit: SF Museum of Art Visit San Francisco Museum of Modern Art and see Abstract Expressionist paintings. Turn in your ticket receipt ($7 for students). Worth one homework assignment; deadline is Oct. 16 th Guardians of the Secret, Jackson Pollock, 1943
Extra Credit: San Jose Ballet See a performance of San Jose Ballet in San Jose Center for Performing Arts (Nov. 15 th – 18 th ). Turn in your ticket receipt. Worth one homework assignment or three quiz/participation credits. Ramon Moreno in CARMINA BURANA
Entropy & The Second Law
First Scientific Discovery Wedge? Wheel? Fire!
Harnessing Heat Thermal energy harnessed in Heating (Furnaces, Heaters) Cooling (Refrigerators, AC) Transportation (Gasoline Engine) Manufacturing (Metallurgy, Plastics) Cooking (Culinary Arts) Arts (Glassblowing) What exactly is heat and how is it related to temperature?
Drawing Hot & Cold Divide a blanck sheet of paper in half. You will create two quick, abstract drawings On one side, draw an image of HOT On the other side, draw an image of COLD Do NOT draw figuratively (dont draw a fire, a snowman, etc.) but instead make a pure abstract drawing. Think HOT (or cold) and draw how it feels.
Hot or Cold?
Bluish colors feel cool while reddish colors feel warm.
Temperature Temperature of an object indicates average internal energy (due to molecular motion) of the object. Temperature Scales Absolute zero is minimum temperature at which molecular motion ceases.
Liquid Nitrogen Nitrogen gas in air becomes a liquid if temperature is lowered to -320 ºF.
Demo: Slowing Air Molecules Cool balloon using liquid nitrogen Air molecules slow down and lose kinetic energy Balloon slowly warms up, restoring energy Balloon returns to its original state
Thermal Expansion Due to increased molecular motion, most materials expand as temperature increases. Sidewalk buckles and cracks due to expansion on a hot summer day Space allows for expansion
Demo: Bi-metallic Strip Different materials have different rates of expansion. STEEL Brass Brass expands more than steel when heated Thermostat Bi-metallic Spiral strip HOT COLD
Demo: The Brittle Onion If frozen solid in liquid nitrogen an onion will shatter like glass since molecules form rigid, brittle lattice. Organic materials appear solid but cells contain large amounts of liquid water.
Heating & Energy Can increase internal energy (and temperature) by tapping energy sources. Chemical energy released in fire Electric energy heats burner
Work and Heat May increase internal energy by exerting a force to do mechanical work. Rub hands together for warmth Strike an iron surface with great force and red-hot sparks are created
Removing Energy Cooling achieved by removing energy, for example, by evaporation of a liquid. GAS LIQUID A random molecule at the surface acquires enough energy to escape the attraction force among the molecules (which holds the liquid together).
Evaporative Cooling Because only the most energetic molecules can escape the surface, evaporation removes internal energy from the liquid, that is, evaporation cools. WET CLOTH Wet towel cools head WET TONGUE Wet tongue cools dog WET BODY & TOWEL Wetness cools person Brr HEAT
Cooling by Expansion When a gas expands it pushes outward with a force. By conservation of energy, the work done by that force equals the internal energy released. Warm Cool Warm breath feels cool when it expands Aerosol spray is cold
Refrigerators Refrigerators and air conditioners cool by evaporation and expansion of a coolant gas.
Freon & Ozone In the 1990s scientists determined that refrigeration coolants, such as Freon, were destroying Earths protective ozone layer. By international treaty the use of harmful coolants was banned. Ozone layer is slowly returning to normal. Ozone hole over Antarctica
Entropy Entropy is the scientific measure of disorder. Molecules in solid ice are very ordered because theyre in a crystal lattice. Molecules in steam are disordered, with random positions and random velocities. Low Entropy High Entropy Think about your drawings of hot and cold?
Heat Flow Heat always flows from high temperature objects to low temperature objects. Heat flow stops when temperatures equal. Various ways by which heat may flow. 98º 32º 75º Heat flows from child and air into the ice cream Heat flows from child into air
Entropy & Second Law Ink & Water INK Water TIME Warm HOT Cold Entropy (disorder) increases with time so ink molecules mix in water Entropy increases with time so heat energy goes from hot to cold
Conduction Conduction is heat flow by direct contact. Some materials are good thermal conductors, others are insulators. 98º 75º 98º 75º Wood is an insulator Tile is a conductor Tile floor feels colder than wood floor
Demo: Torch the Money Wrap a dollar bill tightly around a copper pipe. Put it into a flame. Paper doesnt burn because copper is a very good thermal conductor. Heat from the flame passes into the copper so the paper never reaches ignition temperature (451 ºF).
Air is a Poor Conductor Can safely put your hand in an oven. Metal is good conductor so you need oven mitt to touch it safely (cloth is a poor conductor). Because air is such a poor conductor, some pizza ovens dont have a door.
Convection Heat transfer in a fluid often occurs mostly by convection. Buoyancy causes warm air to rise, which carries thermal energy directly by its motion.
Demo: Candle Very HOT Warm Shadows reveal rising air currents of hot air. Rising hot air above a candle carries most of the heat generated by the burning flame.
Convection Oven Convection oven has a fan to enhance the circulation of the air, increasing the transfer of heat.
Demo: Candle in a Tube Candle stays light until the partition in the tube is removed. Why? Partition allows hot air to rise, drawing in cold air (with fresh oxygen) to fuel the candle flame. Without the partition, turbulence impedes the inflow and outflow. Convection is disrupted because tube is narrow.
Fiberglass Insulation Air is a poor thermal conductor but easily transfers heat by convection. Fiberglass insulation is mostly air, with the fibers disrupting the convection flow.
Radiation Light has many different wavelengths, most of which are not visible to the eye. All light carries energy, thus transfers heat. Heat Lamp
Controlling Heat Transfer Thermos bottle eliminates conduction and convection by having double- walled sides with vacuum. Silvered interior walls minimize heat transfer by radiation.
Greenhouse Effect Glass is transparent to sunlight (short-wavelength). Glass is opaque to infrared radiation (long-wavelength) produced by objects inside greenhouse, trapping the heat.
Earths Greenhouse Effect Earths atmosphere acts as a greenhouse, trapping solar energy. Most of the trapping is due to carbon dioxide and water vapor, which is why theyre called greenhouse gasses.
Global Temperature Variations Temperatures increased from 1910 to Temperatures then cooled for 40 years until they started rising again in the 1980s.
Greenhouse Carbon Dioxide Over past 1000 years temperatures nearly constant until CO2 emissions increased starting with the industrial revolution. Industrial revolution begins
Cars & Carbon Dioxide One gallon of gasoline has about 5.2 lb of carbon. A 5-lb bag of charcoal (which is pure carbon) holds about 100 briquettes. At 26 miles per gallon, thats 0.2 lb of carbon per mile, or about four to five charcoal briquettes per mile.
Anthropogenic * Global Warming Rising temperatures are due to human production of greenhouse gases. * Caused by humans Temperature
Consequences of Global Warming Weather modifications Species extinctions Melting of Polar Ice Caps
Solutions to Global Warming Many simple, small changes together could make a significant difference. Efficient Appliances Building Insulation Efficient Lighting
Next Lecture First Set of Oral Presentations Remember: Oral presentation or term paper due Quiz at the end of class on the material in the oral presentations