Welcome to
Physics 105 - Section 006 !
Instructor: Prof. Ken Ahn
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Today in this class…
1. Physics 105 Course information
2. Brief introduction to Physics
3. Chapter 1. Measurements
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Course information: Instructor
Instructor : Ken Ahn
Office : 483 Tiernan Hall
Phone: 973-596-5227 (office)
E-mail: [email protected]
Web: http://geocities.com/kenahn7
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Course information: Course objectives
1. Understanding the basic principles governing
elementary mechanics (Example: Newton's laws)
2. Applying the basic principles to explain commonly
observed phenomena (Example: free fall motion of an
apple)
3. Improvement of analytical reasoning and problemsolving skills (Example: think like Newton)
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Course information: Hours and websites
Lecture: Thursday 10:00 - 11:25 am, 106 Fac. Mem. Hall
Recitation: Monday 1:00 - 2:25 pm, 106 Fac. Mem. Hall
Office hours: After classes or by appointment
Course website
Phys. 105: http://web.njit.edu/~opyrchaj
Phys. 105, Sect. 006: http://geocities.com/kenahn7
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Course information: Textbook
Halliday, Resnick, and Walker
Fundamentals of Physics, 7th edition
Chapters 1-9th (Part 1)
7th edition:
(HR&W)
6th edition:
Supplemental(not required): Active Physics, 2nd ed.
by Van Heuvelen and Gautreau (Wiley Custom Svc.)
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Course information: Course requisites
Physics 105A: Laboratory course with separate grades
(Check http://physics.njit.edu/classes/physlab)
Physics 105W: Physics-A Workshop
You must be registered for all of Phys 105, Phys 105A
and Phys 105W.
Withdrawal from any of the three
Æ Withdrawal from all other Phys 105 courses.
[Co
Co-requisite:
requisite Math 103 or 111, see “Information for students …”]
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Course information: Attendance
Any student missing a total of 3 classes
(any combination of lecture, recitation, and workshop)
Æ Dropped from the course.
[See “Information for students…”]
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Course information: Grades
• Three Common Exams:
•
•
•
•
(Feb.9, Mar.2, Apr.13)
45% (15% each)
Quizzes during Lect./Reci.: 7%
Homework:
8%
Workshop:
10%
Final exam:
30%
A
B+
B
C+
C
D
F
80+
75-79
70-74
65-69
55-64
50-54
< 50
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Course information: Homework
Homework problem assignment:
Web-based Homework Service at Univ. of Texas
Follow instructions at the course webpage:
http://geocities.com/kenahn7
Reading assignment : essential (see the course schedule)
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Course information: How to do well
•
Keep up!
• Do the homework carefully
and understand the reason
for each step.
• Form a study group to
discuss homework problems.
• Do plenty of extra problems
and examples.
• The material gets more
difficult through the term.
Don’t slack off, even if you
are doing well !
Required level
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Course information: Additional resources
Office hours: After classes on Monday and Thursday
or by appointment
Physics Learning Center:
401 Tiernan Hall, A schedule is posted outside of 401T.
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Intro.to Physics: What is Physics?
¾
¾
Physics (n.) - The branch of science that
deals with the nature and properties of
matter and energy.
Mechanics (n.) - The branch of physics
that deals with the motion and equilibrium
of material bodies and the action of forces.
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Intro.to Physics: Classical Mechanics
Classical Mechanics: Theory that predicts qualitatively
& quantitatively the results of experiments for objects
that are NOT
– too small
atoms and subatomic particles Æ Quantum Mechanics
– too fast
objects near the speed of light Æ Special Relativity
– too dense
black holes, the early Universe Æ General Relativity
Classical mechanics deals with a lot of our daily-life objects !
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Chap.1, Measurement: Section 1-6
• Measuring Things
• International System of Units (SI
System)
• Conversion of Units
• Length
• Time
• Mass
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Ch.1,Measurement: Number and Unit
Being quantitative in Physics requires measurements.
“The length is 100.” has no physical meaning.
Obviously, 100 cm and 100 inches are different !!
Both numbers and units :
necessary for any meaningful physical quantities
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!
t
s
Lo
http://mars.jpl.nasa.gov/msp98/orbiter
Æ Unit is important !
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NASA’s Unit Confusion!
• $125 million Mars climate orbiter approached Mars on
September 23rd, 1999, but crushed or burned in Mars’
atmosphere.
• Built by Lockheed Martin astronautics engineers who
used British system for navigational information.
• Spacecraft operators at NASA jet propulsion lab thought
it was the SI (metric system) as was required.
• Spacecraft was supposedly directed to a safe orbit of
87 mi above Mars’ surface but instead it was only 35 mi.
• Source:
http://www.cnn.com/TECH/space/9909/30/mars.metric
/
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Ch.1,Measurement: Types of quantities
Many things can be measured:
Distance, velocity, energy, time, force…
Æ These are related to one another
(e.g. velocity = distance / time)
Æ Choose three basic quantities:
LENGTH, MASS, TIME
Æ Define other units in terms of these.
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Ch.1 Measurement: Units for length/mass/time
Many possible choices for units of length, mass, time
(e.g., foot and meter for length)
Metric or SI Unit (SI, Système Internationale) since 1971
Æ meter, kilogram, second : human scale
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Ch1.Measurement: SI Length unit Æ meter
French Revolution, 1792
1 meter = |XY|/10,000,000
(1 m = about 3.28 ft)
1 km = 1000 m, 1 cm = 1/100 m, 1 mm = 1/1000 m
Current definition of 1 meter :
Distance traveled by light in a vacuum during 1/299 792 458 of a second
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Ch1.Measurement: SI Time unit Æ second
How can we define time?
Currently, 1 second (s) is defined using “atomic clock”:
time taken 9 192 631 770 oscillations of the light of a specific
wavelength emitted by a cesium-133 atom
Æ Defining unit precisely is a science (important for, for example, GPS):
National Institute of Standard and Technology
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Ch1.Measurement: SI Mass unit Æ kilogram
Current definition of 1 kiligram (kg):
mass of a platinum-iridium cylinder at
International Bureau of Weights and
Measures near Paris
(Copies are kept in all other countries)
Example: Typical mass of an elephant = about 5000 kg
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Ch1.Measurement: Prefix for SI unit
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3000 m = 3 x 1,000 m = 3 x 10 m = 3 km
(1000 = kilo = k)
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1,000,000,000 = 10 = giga = G
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1,000,000 = 10 = mega = M
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1,000 = 10 = kilo = k
Example :
1 kg = 1000 g, 1 Gbyte = 1,000,000,000 byte
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Ch1.Measurement: Prefix for SI unit
-3
0.005 s = 5 x 0.001 s = 5 x (1/1000) s = 5 x 10 s = 5 ms
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(0.001 = 1/1000 = 10 = mili = m)
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0.01 = 10 = centi = c
-3
0.001 = 10 = mili = m
0.000 001 = 10-6 = micro =
µ
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0.000 000 001 = 10 = nano = n
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0.000 000 000 0001 = 10
Example :
= pico = p
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1 nm = 10 m, 3 cm = 0.03 m
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Meter, Second, Kilogram
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Ch1.Measurement: Unit for other quantities
Multiply and divide units just like numbers
Examples
(Speed) = (Distance)/(Time)
(SI unit for speed) = m/sec
(SI unit for area) = m 2
(Area) = (Length) x (Length)
(Volume)=(length)x(length)x(length)
(Mass density)=(Mass)/(Volume)
(SI unit for volume) = m
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(SI unit for mass density) = Kg/m3
You ran 100 m in 20 sec. Your average speed?
100 m 100 m
=
= 5 m/sec
20 sec 20 sec
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Ch1.Measurement: Other unit systems
• British units: foot(ft), slug (for mass), second
1 foot = 30.48 cm, 1 inch = 2.54 cm, 1 mile = 1.609 km
1 mile = 5280 ft , 1 foot = 12 inches
1 slug = 14.59 kg
• Pound(lb), ounce(oz), ton(t) :
the unit for weight (gravitional force), not for mass
Your weight on Moon differs from that on Earth, but your mass doesn’t.
Under “standard” gravitational force
1 lb : weight of 0.456 kg, 1 oz : weight of 28.35 g, 1 ton : weight of 907.2 kg
• More can be found in Appendices A & D in the textbook
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Ch1.Measurement: Changing units
Example:
Convert a speed 60 mile/h into m/sec
1. Put 1’s using unit conversion relations, as many times as necessary.
2. Multiplly or divide numbers and units.
mile
× 1× 1× ... × 1
h
mile 1609 m
1h
1min
= 60
×
×
×
h
1 mile 60 min 60sec
60 × 1609 m
=
×
= 26.8 m/sec
60 × 60 sec
60
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Ch1.Measurement: Precision in quantities
• Uncertainties in measurements: always exist
Ex.)
Measurement : 1.00 m
Uncertainty : ± 0.01 m
or
1%
• Significant figures : physically meaningful numbers
Ex.) Einstein’s height was 172.000000000000 cm.
Einstein’s height was 172 cm.
WRONG in Physics
RIGHT if you measured down to cm
Significant figures of 170 cm might be confusing.
1.7 × 102 cm, or 1.70 ×102 cm : scientific notation
Adding up quantities
3.14 kg + 0.5 kg = 3.6 kg (physics)
3.14 kg + 0.50 kg = 3.64 kg (physics)
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Ch1.Measurement: Dimensional analysis
Example: Dimension
Units for velocity: mile/h, inch/min, km/h, m/s, ….
But, it’s always [Length]/[Time]
Dimension
Sometimes analyzing quantities in [L],[T] & [M] for length, time & mass
helps to find formula.
Example: Dimensional Analysis
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Suppose we know the unit for work is [M][L] / [T]
and unit for force is [M][L]/[T]
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How is the work related to the force?
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[M][L] / [T]
2
= [M][L]/[T]
2
x [L]
(Work)=(Force)x(Distance) : Answer (Eq.7-6 in p.143)
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Today, we learned…
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1. Course information
Example: What is Prof. Ken Ahn’s website address?
http://geocities.com/kenahn7
(Don’t forget 7)
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2. Brief introduction to Physics
Example: What are we going to learn in Physics 105?
a. Quantum mechanics
b. Special relativity
c. Classical mechanics
d. General relativity
Answer : c. Classical mechanics
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3. Chapter 1. Measurement
Example:
What are the three basic units in the SI Unit system?
m (meter), kg (kilogram), s (second)
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Homework problems and due dates
at Homework Service at U. of Texas
( Instruction at the course website:
http://geocities.com/kenahn7)
Reading assignment due coming Monday (Jan. 22th):
Chapter 1, Sections 1-6
Recitation for Chap.1 : Monday, Jan. 22th
Quiz for Chap.1 : During lecture on Thursday, Jan. 25th
If you did not check your attendance, please see me right after class.
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