Upcoming Classes
Tuesday, Sept. 25th
Entropy and the Second Law
Assignment 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, Christopher
For 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,Linda
For everyone else, term paper is due on that date.
Midterm Exam
Midterm 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
TONIGHT!
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.
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
Design
Design is often a blending of art & science
Architecture
Fashion
Design
Product Design &
Graphic Design
Physics of Drapery
Drapery is a surprisingly difficult physics problem
Artist’s drawing
(A. Durer, 1500)
Vera Wang
Wedding Dress
(2006)
Elements of Draping
Proceedings of the
National Academy
of Sciences (2004)
Frank Gehry, Architect
Modern 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?
Disney Concert
Hall, Los Angeles
Hotel in Spain
MIT, Boston
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.
The First Law
PE = 1200 J, KE = 0 J
Energy is the “currency” of motion
PE = 600 J, KE = 600 J
20 m
10 m
6 kg
Roller
Coaster
PE = 0 J, KE = 1200 J
Can calculate the kinetic and potential energy of a falling bowling ball
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
Which ball wins the race, A or B?
Ball on track B has less potential, thus more kinetic
energy (and greater speed) during most of the race.
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)
(FORCE) x (distance)
X X
Ouch!
Not safe if stake
strikes hard skull
Soft,
fleshy
chest
Automobile Safety
Maximizing the distance during impact on the driver
minimizes the force of impact. Used in design of:
Seatbelts
Air Bags
Crumple
Zones
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 Yourself
Slaves 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.
Support
Friction
Pull
LOAD
Ramp (Inclined Plane)
Ramps allow us to lift a heavy object using a
small force by pushing over long distance.
(small force)
X (LONG DISTANCE)
(BIG FORCE)
X (short distance)
Two persons do the same work but exert different forces.
Pyramids
Ramps 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)
Load
Arm
Effort Arm
Fulcrum
(Load force)/(Effort force) = (Effort Arm)/(Load Arm)
Second & Third Class Levers
Load
Arm
Effort Arm
Second Class Lever
(Effort, Load, Fulcrum)
Load
Arm
Effort Arm
Third Class Lever
(Load, Effort, Fulcrum)
Examples of Levers
Scissors
Crowbar
Effort
Load
Fulcrum
Trebuchet
Wheel barrow
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
Support
Weight
Effort
Cantilever
Load
Fulcrum
Fallingwater house (1935)
designed by Frank Lloyd Wright
Piano Key
A piano key a simple
lever that when
pressed down by a
pianist, pushes up
against another
lever, the whippen.
Effort
Whippen
Load
Fulcrum
Whippen Lever
As the capstan pushes up
the whippen, which then
pushes the jack upwards
against the hammer
while pushing the spoon
towards the damper.
Load
jack
whippen
Effort
capstan
Jack & Hammer
Load
Load
Hammer
Effort
Jack
Effort
Jack
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.
Demo: Hanging Hammer
Oddly, the hinge doesn’t open when the
hammer hangs from the board. Why?
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
Center of
Gravity
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 Wheel
Leonardo 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
Effort Arm
appear as if could start
from rest, begin turning
Load
and continue to turn
Effort clockwise forever.
Does not turn at all
because the weights on
the left have a shorter
You might set yourself to prove that by
effort arm than the load
equipping such a wheel with many balances, …
the wheel would stand in perpetual movement.
arm on the right.
But by this you would be deceiving yourself.
Load
Arm
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