Transcript Slide 1

Lecture 1
Ch1. MEASURING
University Physics: Mechanics
Dr.-Ing. Erwin Sitompul
http://zitompul.wordpress.com
Textbook and Syllabus
Textbook:
“Fundamentals of Physics”,
Halliday, Resnick, Walker,
John Wiley & Sons, 8th Extended, 2008.
Syllabus: (tentative)
Chapter 1: Measuring
Chapter 2: Straight Line Motion
Chapter 3: Vector Quantities
Chapter 4: Two- and Three-Dimensional Motion
Chapter 5: Newton’s Law of Motion
Chapter 6: Friction, Drag, and Centripetal Force
Chapter 7: Work-Kinetic Energy Theorem
Chapter 8: Conservation of Energy
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Grade Policy
Grade Point:
85 – 100
70 – 84
60 – 69
55 – 59
0 – 54
:A
:B
:C
:D
:E
(GPA = 4)
(GPA = 3)
(GPA = 2)
(GPA = 1)
(GPA = 0)
 Always bring a scientific calculator to class.
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Grade Policy
Grades:
Final Grade = 10% Homeworks + 20% Quizzes +
30% Midterm Exam + 40% Final Exam +
Extra Points
 Homeworks will be given in fairly regular basis. The average
of homework grades contributes 10% of final grade.
 Homeworks are to be written on A4 papers, otherwise they
will not be graded.
 Homeworks must be submitted on time, one day before the
schedule of the lecture. If you submit late, the penalty will be
–20 points
 There will be 3 quizzes. Only the best 2 will be counted.
The average of quiz grades contributes 20% of final grade.
 Midterm and final exam schedule will be announced in time.
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Grade Policy
 Extra points will be given if you solve a problem in front of the
class. You will earn 1, 2, or 3 points.
 Make up of quizzes and exams will be held within one week
after the schedule of the respective quizzes and exams.
 To maintain the integrity, the score of a make up quiz or exam,
upon discretion, can be multiplied by 0.9 (the maximum score
for a make up is 90).
Basic Physics 1
Homework 6
Rudi Bravo
009201700008
21 March 2021
No.1. Answer: . . . . . . . .
Heading of Homework Papers (Required)
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Lecture Activities
 Lectures will be held in the form of PowerPoint presentations.
 You are expected to write a note along the lectures to record
your own conclusions or materials which are not covered by
the lecture slides.
How to get good grades in this class?
• Do the homeworks by yourself
• Solve problems in front of the class
• Take time to learn at home
• Ask questions
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Lecture Material
 Latest lecture slides will be available on internet. Please
check the course homepage regularly.
 The course homepage is :
http://zitompul.wordpress.com
 You are responsible to read and understand the lecture
slides. I am responsible to answer your questions.
 Quizzes, midterm exam, and final exam will be open-book. Be
sure to have your own copy of lecture slides. You are not
allowed to borrow or lend anything during quizzes or exams.
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The International System of Units
 Physics is based on measurement.
 Each physical quantity is measured in its own units, by
comparison with a standard.
 The exact definition of a unit is arbitrary, but is chosen so that
scientists around the world will agree that the definitions are
both sensible and practical.
 By international agreement, there are seven base quantities:
 length (unit name: meter, unit symbol: m)
 mass (kilogram, kg)
 time (second, s)
 electric current (ampere, A)
 thermodynamic temperature (kelvin, K)
 amount of substance (mole, mol)
 luminous intensity (candela, cd)
 All other physical quantities are defined in terms of these
base quantities and their standards (called base
standards).
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The International System of Units
 For University Physics: Mechanics, we will use the base
quantities length, time, and mass.
 From these we can define, or derive other quantities that we
will discover as we proceed:
 Velocity (length/time)
 Acceleration (velocity/time, or length/time2)
 Force (massacceleration or masslength/time2)
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Scientific Notation and Ten Power Prefixes
 To express the very large and very
small quantities that we often meet in
physics, we use scientific notation,
which employs powers of 10.
 3 560 m = 3.56  103 m
= 3.56 kilometers
= 3.56 km
 0.000 000 492 s = 4.92  10–7 s
= 0.492  10–6 s
= 0.492 microseconds
= 0.492 μs
 1.27  109 watts = 1.27 gigawatts
= 1.27 GW
 What about millimeter, centimeter,
kilogram, megabyte, megahertz?
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Changing Units
 We often need to change the units in which a physical
quantity is expressed.
 In doing so, we use a method called chain-link conversion.
 The original measurement is multiplied by a conversion
factor (a ratio of units that is equal to unity).
1 min
1
in
1 min  60 s 
 1 1 in  2.54 cm 
 1
60 s
2.54 cm
s
cm
 60
 1
 2.54
 1
min
in
Example:
Convert 2.5 hours into seconds.
Solution:
60 min 60 s
 (2.5)(60)(60) s  9000 s
2.5 hours  2.5 hours 

1 hour 1 min
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Changing Units
Example:
A PU student goes to Jakarta using Bus 121
(Blok M – Cikarang, via Semanggi, Rp.9.000,-).
As the bus drives on the toll road, the student
measures the time needed by the bus to travel between
km 20.0 and km 19.0 using his stopwatch.
If the stopwatch shows that the time is 42 s, determine the
average velocity of the bus in km/h.
Solution:
v avg
1 km 60 s 60 min 60  60




 85.714 km/h
42 s 1 min
1h
42
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Length
 In 1792, the newborn Republic of France
established a new system of weights and
measures.
 1 meter is defined to be one ten-millionth of
the distance from the north pole to the
equator.
 Later in 1889, the meter came to be defined
as the distance between two fine lines
engraved near the ends of a platinum-iridium
bar (standard meter bar).
 In 1960, a new standard for the meter, based
on the wavelength of light, was adopted.
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Length
 The standard meter was redefined
to be 1 650 763.73 wavelengths of
orange-red light emitted by atoms of
krypton-86 in a gas discharge tube.
 The current definition of the meter is
created in 1983, which is the length
of the path traveled by light in a
vacuum during a time interval of
1/299 792 458 of a second.
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Pronunciation of Mathematical Expressions
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Time
 In old definition, any time
standard was calibrated against
Earth’s rotation via astronomical
observations.
 In this way, 1 second is
1/86 400 of the time for a
complete earth rotation.
 However, the accuracy cannot
meet the accuracy called for by
modern scientific and
engineering technology.
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Time
 To meet the need for a better time
standard, atomic clocks have been
developed.
 In 1967, a standard second based
on the cesium clock was adopted.
 One second is the time taken by
9 192 631 770 oscillations of the
light (of a specified wavelength)
emitted by a cessium-133 atom.
The first atomic clock, developed in 1955
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Mass
 Originally, the standard of mass is the weight of the water.
1 kilogram was defined as the mass of 1000 cubic
centimeters of water.
 The current SI standard of mass is a
platinum-iridium cylinder kept at the
International Bureau of Weights and
Measures near Paris. It is assign, by
international agreement, a mass of
1 kilogram.
 Accurate copies have been sent to
standardizing laboratories in other countries,
and the masses of other bodies can be
determined by balancing them against a
copy.
 The second mass standard is the atomic mass units (u).
The carbon-12 atom, by international agreement, has been
assigned a mass of 12 u, with 1 u = 1.660 538 86  10–27 kg.
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Mass
KOMPAS, 11 March 2012
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Trivia
Eight eggs look identical except one is lighter.
How can you weigh only 2 times on a balance
scale to find out which one is lighter?
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Trivia
Solution:
• We number the eggs, from 1 to 8.
• Put egg 1, 2, and 3 on the left and
egg 4, 5 and 6 on the right and weight them.
• If they are balanced then we know egg 1 to 6 are all
identical. We just need to put egg 7 on one side and egg 8
on the other side and weight them. The lighter egg is found.
If they are not balanced, assuming the left side is lighter, put
egg 1 on the left, egg 2 on the right, weight them one more
time.
If egg 1 and egg 2 are still balanced, then egg 3 is lighter.
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Lecture 1
Ch2. STRAIGHT LINE MOTION
University Physics: Mechanics
Dr.-Ing. Erwin Sitompul
http://zitompul.wordpress.com
Position and Displacement
 To locate an object means to find its position relative to
some reference point, often the origin (or zero point) of an
axis.
 The positive direction of the axis is in the direction of
increasing numbers (coordinates).
 The opposite direction is the negative direction.
 A change from one position x1 to another position x2 is
called a displacement Δx, where
x  x2  x1
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Average Velocity and Average Speed
 Average velocity (vector) = ratio of the displacement to the
time interval
x
x2  x1
vavg 

t
t2  t1
 Average speed (scalar) = ratio of the total distance traveled
to the time interval
savg 
total distance
t
 Note that the average velocity points in the
same direction as the displacement vector
 If the displacement points in the +
direction, then the velocity is +
 If the displacement points in the –
direction, then the velocity is –
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Average Velocity and Average Speed
 Circuit Length:
 Number of Laps:
 Race Distance:
 Time:
5.419 km
57
308.883 km
1:35:51.289
Rubens Barrichello won the European GP
in Valencia on 23 August 2009
 What is Rubens’ average velocity
in km/h?
vavg  0
 What is Rubens’ average speed
in km/h?
308.883 km
savg 
 193.344 km/h
1.59758 h
Erwin Sitompul
The start and finish lines
are identical, so Rubens’
displacement after 57 laps
is zero.
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Average Velocity and Average Speed
 Average velocity can be found a graph of x versus t, which
is equal to the slope from the initial to the final position.
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Average Velocity and Average Speed
 Position vs. Time graph or
x-t graph
vavg > 0
vavg < 0
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Average Velocity and Average Speed
• So for the round trip, your displacement
Δx = x2–x1 = 0, and your average
velocity vavg = Δx / Δt = 0.
• However, your average speed was
40 km/h.
At time t1 = 0, your
position is x1 = 0
Erwin Sitompul
At time t2 = 30 min, your
position is x2 = 0
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Questions
The figure below shows four paths along which objects move
from a starting point to a final point, all in the same time. The
lines are equally spaced. Rank the paths according to
(a) The average velocity of the objects.
All tie
(b) The average speed of the objects.
4, tie of 1 and 2, 3
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Example: Grand Livina
You drive a Grand Livina from city J to city B, which are
separated by 150 km, with a constant velocity of 80 km/h. After
reaching B, you directly travel back to city J, with constant
velocity of 60 km/h.
What is your average speed?
150 km
tJB 
 1.875 h
80 km/h
150 km
tBJ 
 2.5 h
60 km/h
savg 
distance
Erwin Sitompul
t

dist JB  dist BJ
tJB  tBJ
150 km  150 km

 68.57 km h
1.875 h  2.5 h
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Homework 1: Truck
You drives a truck along a straight road for 8.4 km at 70 km/h,
at which point the truck runs out of gasoline and stops. Over
the next 30 min, you walk another 2.0 km farther along the road
to a gasoline station.
(a) What is your overall displacement from the beginning of
your drive to your arrival at the station?
(b) What is the time interval Δt from the beginning of your drive
to your arrival at the station?
(c) What is your average velocity vavg from the beginning of
your drive to your arrival at the station? Find it both
numerically and graphically.
(d) Suppose that to pump the gasoline, pay for it, and walk
back to the truck takes you another 45 min. What is your
average speed from the beginning of your drive to you
return to the truck with the gas?
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Homework 1A: Car
New
You start driving a car with constant velocity to a shopping
center at 10:15. The road is straight and the shopping center is
6 km away from your initial position. At 10:35 you are only 2 km
away from destination and make a stop.
(a) What is your average velocity vavg from the beginning of
your drive to your stop?
(b) After a very short stop, you continue driving. You want to
reach the shopping center at 10:40, how fast do you have
to drive the rest of the distance?
(c) You reach the destination exactly at 10:40. What is your
average velocity vavg from the beginning of your drive to
your arrival at the shopping center?
(d) Draw the graph of your movement (time against position).
Homeworks are to be written on A4 papers
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Homework 1B: Interview
New
You are to drive to an interview in another town, at a distance of
300 km on an expressway. The interview is at 11:15. You plan
to drive at 100 km/h, so you leave at 8:00 to allow some extra
time.
You drive at that speed for the first 100 km, but then
construction work forces you to slow to 40 km/h for 60 km.
(a) What would be the least speed needed for the rest of the
trip to arrive in time for the interview?
(b) Draw the graph of your movement (time against position).
(c) If the maximum allowable speed on the expressway is 120
km/h, how long does the interviewer have to wait?
Homeworks are to be written on A4 papers
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