Upcoming Classes Tuesday, Oct. 9 th Dissecting the iPod Assignment due: * Homework #4 (Egg...
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Transcript of Upcoming Classes Tuesday, Oct. 9 th Dissecting the iPod Assignment due: * Homework #4 (Egg...
Upcoming Classes
Tuesday, Oct. 9th
Dissecting the iPodAssignment due:
* Homework #4 (Egg container)
Thursday, Oct. 11th
Design at the Nexus
Assignment due:
* Topic and outline for second paper or oral presentation
Upcoming Deadlines
Thursday, October 11th
Outline of second oral presentation or written paper
Tuesday, November 6th
Second Set of Oral Presentations
Second term paper (if not presenting)
Oral Presentations (II)
The following persons will give oral presentations on Tuesday, November 6th :
• Luttrell,Katherine• Macdonald,Keith• McDonald,Kathleen• Mendoza,Jazmin• Nguyen,Jennifer• Nguyen,LindaFor 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. 16th
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. 15th – 18th ).
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 (don’t 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?
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-metallicSpiral 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
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.
WETCLOTH
Wet towel cools head
WETTONGUE
Wet tongue cools dog
WETBODY &TOWEL
Wetness cools person
Brr
HEAT
HEATHEAT
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 1990’s scientists determined that refrigeration coolants, such as Freon, were destroying Earth’s protective ozone layer.
By international treaty the use of harmful coolants was banned.
Ozone layer is slowly returning to normal. Ozone hole over Antarctica
EntropyEntropy is the scientific measure of disorder.
Molecules in solid ice are very ordered because they’re in a crystal lattice.
Molecules in steam are disordered, with random positions and random velocities.
LowEntropy
HighEntropy
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 fromchild and air into the ice cream
Heat flows fromchild into air
Entropy & Second Law
Ink & Water
INK
Water
TIM
E
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 aninsulator
Tile is aconductor
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 doesn’t 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 don’t 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: CandleVery HOT
Warm
Shadows revealrising air currents of hot air.
Rising hot air above a candle carries most of the heat generated by the burning flame.
Convection OvenConvection 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 EffectGlass is transparent to sunlight (short-wavelength).
Glass is opaque to infrared radiation (long-wavelength) produced by objects inside greenhouse, trapping the heat.
Earth’s Greenhouse Effect
Earth’s atmosphere acts as a greenhouse, trapping solar energy.
Most of the trapping is due to carbon dioxide and water vapor, which is why they’re called “greenhouse gasses.”
Global Temperature Variations
Temperatures increased from 1910 to 1940.
Temperatures then cooled for 40 years until they started rising again in the 1980’s.
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, that’s 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
Tem
pera
ture
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