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