Upcoming Classes

Tuesday, Sept. 25th

Entropy and the Second LawAssignment due:

* Read “Exploiting Heat”, The New Way Things Work,

D. Macaulay, Pages 142-157

Thursday, Sept. 27th

First set of Oral Presentations

Assignment due:

* First term paper or oral presentation

Upcoming Classes

Thursday, Sept. 27th

First set of Oral Presentations

Assignment due:

* First term paper or oral presentation

Tuesday, Oct. 2nd

Midterm Exam

Assignment due:

* Study for the midterm

Upcoming Deadlines

Thursday, September 27th

First Set of Oral Presentations

First term paper (if not giving presentation)

Thursday, October 11th

Outline of second oral presentation or written paper

Oral Presentations

The following persons will give oral presentations on Thursday, September 27th :

• Batres, Adan• Boyd, Heidi• Chen, Emily• Kwiatkowski, Dajon• Lebedeff, Christopher• Lipton, ChristopherFor everyone else, your first term paper is due on

that date.

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.

Midterm ExamMidterm exam will consist of four short essay questions.

Material up to and including: “Energy and the First Law” lecture; “The Mechanics of Movement” reading.

Closed book but allowed one page of notes (front & back).

Sample questions:

“List three ways that a painter can create a sense of distance in a painting. Describe one of the ways in detail.”

“What is a fractal? Give two examples of fractals and an example of something that is not a fractal.”

“Explain the physics of balance. Give examples related to dance.”

Midterm counts for one homework assignment.

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

Extra Credit: Cypress Quartet

SJSU Celebrates 150th with Cypress String Quartet Event Fusing Precision Playing with World-Class Technology

SJSU Music Concert Hall, 7 p.m. Thur., Sept. 20th.I will hand out tickets at the door from 6:30 to 6:50pm; don’t be late to the performance! Worth two quiz/participation extra credits.

TONIGHT!

David Chai, Animator

Your flip-book homework was judged by David Chai of Thunderbean Animation Studios and San Jose State University.

Energy & The First Law

DesignDesign is often a blending of art & science

Architecture

FashionDesign

Product Design &Graphic Design

Physics of Drapery

Artist’s drawing(A. Durer, 1500)

Vera WangWedding Dress

(2006)

Elements of Draping Proceedings of the National Academy of Sciences (2004)

Drapery is a surprisingly difficult physics problem

Frank Gehry, ArchitectModern engineering and science tell us that the designs of Frank Gehry can be built and are safe.

Fundamental question in design: What are the limitations placed by the laws of physics?

Hotel in Spain

MIT, BostonDisney Concert Hall, Los Angeles

Fundamental Design Questions

Can you design a machine that creates a large force using a small force?

Can you design a machine that creates a lot of energy using a little energy?

Burj Dubai

Hybrid car

Kinetic Energy (KE)

Kinetic energy is energy of motion.

Kinetic energy of an object is,

(Kinetic Energy) =

½ x (Mass) x (Speed)2

A stationary object has zero kinetic energy.

Supertanker and bullet both have large kinetic energies

Potential Energy (PE)

Gravitational potential energy of an object is,

(Potential Energy) = (Weight) x (Height)

Think of potential energy as stored energy or energy “in the bank.”

Metric unit of energy is Joules.

10 m

PE = 600 J, KE = 600 J

The First Law20

m

6 kgPE = 1200 J, KE = 0 J

PE = 0 J, KE = 1200 J

Energy is the “currency” of motion

Can calculate the kinetic and potential energy of a falling bowling ball

Ramp

RollerCoaster

Conservation of Energy

Conservation of mechanical energy is

(Potential Energy) + (Kinetic Energy)

stays constant during motion.

Energy “bookkeeping” makes motion simple.

Types of Energy

In this lecture we’ll consider mechanical energy but there’s also:

• Thermal energy• Chemical energy• Electrical energy• Solar energy*• Nuclear energy

Total energy is conserved, once we account for the various different forms it can transform into.

* Actually a form of electrical energy

Demo: Ball Races

Ball on track B has less potential, thus more kinetic energy (and greater speed) during most of the race.

Which ball wins the race, A or B?

Energy and Force

To stop an object with a large kinetic energy requires either:

• Large force (stopping the object quickly).

• Small force applied for a long distance.

Notice that changing object’s energy depends on force and distance.

Demo: Egg Throw

Throw a raw egg as fast as possible at a plastic sheet that’s held loosely.

X X

X

X

X (Hold here)

Demo: Vampire Stake

Place a heavy stake on my chest and strike with a hammer. Why am I not killed?

(force) x (DISTANCE)

X XOuch!

(FORCE) x (distance)

Not safe if stake strikes hard skull

Soft, fleshychest

Automobile SafetyMaximizing the distance during impact on the driver

minimizes the force of impact. Used in design of:

Seatbelts Air Bags CrumpleZones

Work

Define work done on an object by a force as

(Work) = (Force) X (Distance traveled)

Force acting in direction of motion: Positive work.

Force acting in opposite direction: Negative work.

Force perpendicular to motion: Zero work

Change in energy equals the work done on by forces

Check YourselfSlaves pull a heavy load.

Work done by slaves is positive, negative, or zero?

Positive work.

Work done by friction force?

Negative work.

Work done by the ground?

Zero. Support does no work.LOAD

SupportPull

Friction

Ramp (Inclined Plane)Ramps allow us to lift a heavy object using a

small force by pushing over long distance.

(BIG FORCE) X (short distance)

(small force) X (LONG DISTANCE)

Two persons do the same work but exert different forces.

PyramidsRamps allowed ancient civilizations to lift enormous stones to build pyramids

Knife

Knife is a wedge that exerts a large force over a small distance by exerting a small force over a large distance.

Push down large distance with small force

Wedge exerts large force for a small distance

Zipper

The zipper, patented in 1917, has interlocking teeth separated or joined by a wedge.

Wedge

Gideon Sundback’s patent for the "Separable Fastener"

Lever

Lever also converts a small force into a large force by ratio of distances acting.

Push down with a small force over a large distance

Lift a large weight over a small distance

First Class Levers

Fulcrum is located in between the input force (effort) and the output force (load)

Fulcrum

Effort ArmLoadArm

(Load force)/(Effort force) = (Effort Arm)/(Load Arm)

Second & Third Class Levers

Third Class Lever(Load, Effort, Fulcrum)

Second Class Lever(Effort, Load, Fulcrum)

Effort Arm

LoadArm

Effort Arm

LoadArm

Examples of Levers

Crowbar

Wheel barrow

Scissors

Trebuchet

EffortLoad

Fulcrum

Human Arm as a Lever

Bicep muscle exerts an effort force close to your elbow (fulcrum) to raise your forearm (load).

This is a third class lever so a large effort force acts over a small distance to move a small load over a large distance.

Cantilever

Cantilevers are used in architecture to support hanging beams and platforms

CantileverEffort

LoadFulcrum

Fallingwater house (1935)designed by Frank Lloyd Wright

SupportWeight

Piano Key

A piano key a simple lever that when pressed down by a pianist, pushes up against another lever, the whippen.

Whippen

Effort

Load Fulcrum

Whippen LeverAs the capstan pushes up

the whippen, which then pushes the jack upwards against the hammer while pushing the spoon towards the damper.

whippen

jack

capstanEffort

Load

Jack & Hammer

Jack rises, pushes the hammer towards the string, then is pulled away from the hammer when it hits the letoff button. Hammer swings and hits the string.

JackJack

Hammer

Effort

Load

Effort

Load

Demo: Hanging Hammer

Oddly, the hinge doesn’t open when the hammer hangs from the board. Why?

Center ofGravity

If the hinge opened then the center of gravity, located near the hammer’s head, would rise. This would be a spontaneous increase in the potential energy of an object at rest. That’s impossible, in the same way that a ball won’t spontaneously roll uphill.

Hinge

Perpetual Motion Machines

Is it possible to design a machine that runs forever, creating its own source of energy?

No. By the First Law, energy may be transferred from one form to another but it may neither be created nor destroyed.

Perpetual motion machines are impossible, but that’s not stopped people from trying.

Overbalanced WheelLeonardo da Vinci’s notebooks show his analysis of perpetual motion ideas that originated in 8th century India and reached Europe via Arabia

Wheel seems to perpetually turn due to imbalance between left and right sides

Perpetual Motion & Levers

Overbalanced wheel may appear as if could start from rest, begin turning and continue to turn clockwise forever.

Does not turn at all because the weights on the left have a shorter effort arm than the load arm on the right.

Effort

Load

Effort ArmLoadArm

You might set yourself to prove that by equipping such a wheel with many balances, … the wheel would stand in perpetual movement. But by this you would be deceiving yourself.

Leonardo da Vinci

Perpetual Motion & Ramps

Will the chain of balls rotate clockwise or counter-clockwise?

Neither since the energy gained going up one side of the ramp exactly equals the energy lost going down the other side.

U.S. Patent Office

From General Information Concerning Patents:“A working model, or other physical exhibit, may

be required by the Office if deemed necessary. This is not done very often. A working model may be requested in the case of applications for patent for alleged perpetual motion devices.”

"It may be perpetual motion, but it will take forever to test it."

Cartoon by Donald Simanek.

Next Lecture Entropy & the Second Law

Remember:Assignment due:

Read “Exploiting Heat”, The New Way Things Work, D. Macaulay, Pages 142-157