University Physics: Mechanics Ch1. MEASURING Lecture 1 Dr.-Ing. Erwin Sitompul .

University Physics: Mechanics

Ch1. MEASURING

Lecture 1

Dr.-Ing. Erwin Sitompulhttp://zitompul.wordpress.com

1/2Erwin Sitompul University Physics: Mechanics

Textbook and Syllabus

Textbook:“Fundamentals of Physics”, Halliday, Resnick, Walker, John Wiley & Sons, 8th Extended, 2008.

Syllabus: (tentative)Chapter 1: MeasuringChapter 2: Straight Line MotionChapter 3: Vector QuantitiesChapter 4: Two- and Three-Dimensional MotionChapter 5: Newton’s Law of MotionChapter 6: Friction, Drag, and Centripetal ForceChapter 7: Work-Kinetic Energy TheoremChapter 8: Conservation of Energy


Grades

Grade Point:85 – 100 : A (GPA = 4)70 – 84 : B (GPA = 3)60 – 69 : C (GPA = 2)55 – 59 : D (GPA = 1)0 – 54 : E (GPA = 0)

Always bring a scientific calculator to class.


Grades

Grades:Final Grade = 5% Homework + 30% Quizzes +

30% Midterm Exam + 40% Final Exam + Extra Points

Homeworks will be given in fairly regular basis. The average of homework grades contributes 5% of final grade.

Homeworks are to be written on A4 papers, otherwise they will not be graded.

Homeworks must be submitted on time. If you submit late,< 10 min. No penalty10 – 60 min. –40 points> 60 min. –60 points

There will be 3 quizzes. Only the best 2 will be counted. The average of quiz grades contributes 30% of final grade.

Midterm and final exam schedule will be announced in time.


Grades

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 one week after the schedule of the respective quizzes and exams.

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).


Lecture Activities The lectures will be held every Tuesday:

17:30 – 18:30 : Class 18:30 – 19:00 : Break19:00 – 20:30 : Class

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


Lecture Material Latest lecture slides will be available on internet every Wednesday afternoon. 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.


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).


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 (massacceleration or masslength/time2)

The International System of Units


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?


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 60 s 1 min 1

60 s

s60 1

min

1 in 2.54 cm 1 in 1

2.54 cm

cm2.54 1

in

Example:Convert 2.5 hours into seconds.

Solution:60 min

2.5 hours 2.5 hours1 hour

60 s

1 min (2.5)(60)(60) s 9000 s


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:

avg

1 kmv

42 s

60 s

1 min

60 min

1 h

60 60

42

85.714 km/h


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.


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.


Pronunciation of Mathematical Expressions


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.


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


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 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.

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.


Mass


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?


TriviaSolution:• 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.

University Physics: Mechanics

Ch2. STRAIGHT LINE MOTION

Lecture 1

Dr.-Ing. Erwin Sitompulhttp://zitompul.wordpress.com


Position and Displacement

A change from one position x1 to another position x2 is called a displacement Δx, where

2 1x x x

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.


Average Velocity and Average Speed Average velocity (vector) = ratio of the displacement to the

time interval

avg

xv

t

2 1

2 1

x x

t t

Average speed (scalar) = ratio of the total distance traveled to the time interval

avg

s

t

total distance

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 –


Average Velocity and Average Speed

Circuit Length: 5.419 km Number of Laps: 57 Race Distance: 308.883

km Time:

1:35:51.289

Rubens Barrichello won the European GP in Valencia on 23 August 2009

What is Rubens’ average speed?

avg

308.883 km

1.59758 hs 193.344 km/h

What is Rubens’ average velocity?

avg 0v

The start and finish lines are identical, so Rubens’

displacement after 57 laps is zero.


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.


vavg > 0

vavg < 0

Average Velocity and Average Speed Position vs. Time graph orx-t graph


At time t1 = 0, your position is x1 = 0

At time t2 = 30 min, your position is x2 = 0

• 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.

Average Velocity and Average Speed


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.

(b) The average speed of the objects. All tie

4, tie of 1 and 2, 3


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?

JB

150 km

80 km/ht 1.875 h

BJ

150 km

60 km/ht 2.5 h

avgs t

distance 150 km 150 km

1.875 h 2.5 h

JB BJ

JB BJt t

dist dist

68.57 km h


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?

Homeworks are to be written on A4 papers


Homework 1

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) In case, if you want to reach the shopping center exactly at 10:40, how fast do you have to drive the rest of the distance?

(c) You drive too slow and eventually reach the destination at 10:45. 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).

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