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Physics 214 Physics of everyday phenomena

Professor Laszlo J. Gutay Office room 314 gutay@purdue.edu

Course Web site http://www.physics.purdue.edu/phys214

CHIP (Computerized Homework in Physics)

http://chip.physics.purdue.edu/public/214/spring2017

Announcements, Syllabus, Schedule, Lecture notes Lists lecture schedule

Times and place of the two evening exams

Deadlines for Homework and Pre-Lecture Quizzes

Use of the I clicker

Useful information

Undergrad Office Room 144, Questions

This Week

• Introduction

• Syllabus, CHIP, Office hours

• Grading

• Exams, I clicker, Lecture quiz

• General

• Who am I, our Universe

• Lecture

• Ch 1,2 Straight line motion

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The Book

Book : Physics of Everyday Phenomena

5th, 6th, 7th or 8th edition

OUTLINE

CHAPTER MATERIAL

QUESTIONS/EXERCISES

HOME EXPERIMENTS AND OBSERVATIONS

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Course Outline

The lecture schedule and reading assignments are

shown in the syllabus. In practice this might change but we

will always be ahead of the homework.

I will do many demonstrations in class and questions on these

will be on the exams.

There will be two 2hours evening exams and a two hours final exam.

We will be using I clickers for in class quizzes and checking attendance.

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Reading and Problems

It is very important that you Read the chapter material which is related to the

lecture Work some questions, exercises and problems Answers are in appendix d for: Questions Every 6th question starting with #3 Exercises Odd numbered Problems Odd numbered Lectures will be posted on the Web weekly Usually the Sunday at the start of the week

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CHIP (Computerized Homework in Physics)

There are 28 Homework assignments.

First one is due by Friday morning January 13.

There are 36 Pre lecture quizzes.

First one due by 8:30am Wed. January 11.

IMPORTANT Read the QUICK GUIDE TO CHIP handout and login

to the CHIP site today and make sure your Career ID and password

work. There is a much longer guide to CHIP that you can access

from the course home page.

You must also register the serial number of your I Clicker in the

student grade book of CHIP

It is very unlikely that there are any errors in CHIP if it will not

accept your answer then you have made an error. Most common

errors are

Wrong answer, Significant figures, Wrong sign

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Getting Help

There are two levels of help

• See me after lecture and make an appointment

• See the T.A. in Help Center Room 12A Thursday afternoon

3:00-7:00pm. His name: Sen Dai

Exams

Exam 1 Feb. 23. Ch 1-6 8 – 10pm Phys. Room 112

Exam 2 April 06. Ch 7-12 8 – 10pm Phys. Room 112

There will be an evening help session before each

exam.

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Who am I • As Physics Student I led the armed uprising in

October 1956, sixty years ago in Hungary • I’m an experimentalist in High Energy or

Elementary Particle Physics trying to find/understand

The physical laws which govern the Universe The fundamental building blocks of all matter The evolution of the Universe from the Big Bang

to the present day, 13.6 billion years later We use Particle accelerators which produce collisions with

energy densities the same as a billionth of a second after the big bang.

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Large Hadron Collider The worlds highest energy collisions in

Geneva, Switzerland. 18 miles in

circumference with 800,000 liters of

liquid Helium (the coldest place in the

entire Universe)

Proton Proton

Energy density is the same as a billionth of a second after the Big Bang which produced the building blocks of our Universe

E=mc2

Higgs Boson

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In 2013 You may have seen a lot of publicity concerning the

discovery of what is the Higgs boson, suggesting the existence of

the Higgs field which gives mass to all particles.

Just as the gravitational field gives weight to an object

and the Electromagnetic field makes two magnets “heavy” by

pulling them together or pushing them apart

the Higgs field permeates the whole Universe and interacts with

all particles to give them mass.

Our picture of how objects interact is by having particles

exchanged, like throwing a football back and forward

So every field has an associated particle . The Higgs particle is

about 125 times the mass of the proton and required very high

energy to produce it at the Large Hadron Collider

This week

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• Our Universe

• Our World

• How do we measure quantities:

time, position, mass

How do we describe the motion of moving

point objects

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What is Physics

Physics is the study of motion, the five forces of interactions and the origin of mass from particles to astrophysical objects. At very small distances: atoms, nuclei, quarks… At extreme energies – Big Bang At extreme velocities - relativity On earth and throughout the Universe and back in time

to 13.7 billion years ago – using Hubble, Cobe, and WMAP spacecraft's and the LHC collider.

We are able to explore and understand the whole Universe from a billionth of a second after the big bang to today and also predict the future.

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Where are we? Light Year: the distance that light travels in one year (9.46 x 1017 cm).

•186282x365.242x24x3600x5280x30.48

•1.86282x105x3.65242x102x24x3.6x103x5.280x103x30.48

The nearest star (other than the sun) is 4.3 light years away. Our Galaxy (the Milky Way) with 100 billion stars is about 100,000 light years in diameter. Number of stars in the Universe is ~ 1028

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Forces and Particles Fundamental forces are what has shaped the Universe and are responsible for all the phenomena we see in our everyday life.

There are only 5 forces

1. Strong Force – holds the protons and neutrons of the nucleus

together

2. Weak Force – responsible for radioactive decay of particles and nuclei

3. Electromagnetic force – Holds electrons in atoms, generates electrical

currents, magnetism and light

4. Gravitation - Attractive force between massive objects, solar system

5. Dark Energy and Matter, a mysterious force which expands space

Every force has a force carrier particle.

Presently known are: Strong interaction force carrier: the gluon g

Weak interaction force carriers: W and Z

Electromagnetic force carrier: the photon

Gravitational force carrier: the graviton G

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Structure and Forces 1. Gravitation

Solar system

galaxies

falling objects

2. Electric charge

everything not gravity

biology

photosynthesis

cars, planes

F

F

F

F

3. Strong Force

+ electron

Neutron Proton

4. Weak Force

The basic carrier of electric charge

and electric current is the electron

(Franklin)

Radioactive decay

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Building blocks

There are two kind of Building blocks

A.) Mass carrier particles:

Quarks – up, down, strange, charm, beauty, top

Leptons - electron, muon, tau, 3 neutrinos

B.) Force carrier particles (Bosons): γ, g, W, Z

Missing pieces

Building blocks – supersymmetric particles…

Questions – Dark energy, dark matter…..

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The Universe

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Large scale structure

•

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The Universe at 300,000 years

2.70 K relic radiation from 300,000

years after the big bang

Observation and Everyday life

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In our everyday life one can make observations and ask why?

The fundamental physical laws and in particular forces are

responsible for all the phenomena we observe.

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Fundamentals As we observe the world around us we need to describe it in the language of mathematics.

We need the fundamental quantities and the relation between them

Length (distance)

Time

Mass

Described in a Coordinate system (reference

point, direction, clock)

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Units and definitions Over the few thousand years of science there have been many systems of units but the system of choice is the SI system

http://unicon.netian.com/unitsys_e.html

SI

Length – hand, foot, mile,… meter

Time – sundial, water clock, second

Direction – north, south, east, west Cartesian

Mass – pound, ton, gram… kilogram

Volume – peck, bushel, cup … cubic meter

Area - acre, square mile, hectare square meter

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Consistency

We always need to use consistent units so that in equations such as A = B + C the quantities A, B, C have the same units.

We may need to convert units to be consistent

Your answers to problems must also have units.

You do not always have to convert to SI units. For example if you travel 60 miles in two hours then your average speed is 30 miles per hour and you do not convert to meters/second unless you are specifically asked to do so.

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Conversions, prefixes and scientific notation

giga 1,000,000,000 109 billion

mega 1,000,000 106 million

kilo 1,000 103 thousand

centi 1/100 0.01 10-

2

hundredth

milli 1/1000 0.00

1

10-

3

thousandth

micro 1/1,000,000 1/106 10-

6

millionth

nano 1/1,000,000,000 1/109 10-

9

billionth

1 in 2.54cm

1cm 0.394in

1ft 30.5cm

1m 39.4in 3.281ft

1km 0.621mi

1mi 5280ft 1.609km

1lb 0.4536kg g =9.8

1kg 2.205lbs g=9.8

Appendix b

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Average speed

Average speed = distance/time s = d/t = 260/5 = 52mph

Units meters/second

kilometers/second

miles/hour

feet/second

Average speed is a positive number

52mph = 52x5280/3600 = 76.26666666 = 76.27 feet/sec

(60mph = 88ft/sec)

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Instantaneous speed

Instantaneous speed is what you see on your speedometer. This is the average speed for a very short time and displacement intervals s = ∆d/Δt We can plot speed versus time and obtain a graph which has all the information for the journey of a moving car

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Scalar and Vector quantities Quantities which can be quantified by one number are called scalars: mass, temperature Quantities which can be quantified by three numbers are called vectors In addition to knowing average speed or instantaneous speed we need to know the direction. The quantity which gives both speed and direction is the velocity. Velocity is an example of a vector quantity and is represented in a “picture” by an arrow, giving the direction and the length of the arrow proportional to the magnitude. Examples for vectors:

To specify direction of a vector we need a coordinate system.

Velocity:

Acceleration:

Force:

Momentum:

Further details in the textbook see Appendix c

v

aF

p

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Coordinate systems

We live in a three dimensional world so the general coordinate system uses three axes at right angles x, y, z. In our discussion we will use rectangular, write handed (Cartesian) coordinate systems in one or two dimensions only.

+

+

-

- x

y N

W

S

E

This was invented by Descartes. Cartesian is the Latin translation of his name

X +

Origin x=0, y=0

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Motion in a straight line along the X axis

d is the distance from the

starting point.

The starting point is

where the particle is at

t=0

1 Constant velocity +

2 Stopped

3 Constant velocity +

4 Constant velocity -

1

2 3 4

- + x d

0 starting point

0 0

, if it started from origin at 0

, if it started from at 0

x vt t

x vt x x t

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Acceleration

A change in velocity is called acceleration . If the increase of the time of the average acceleration t is “large”, we write: . Incase of instantaneous acceleration both are infinitesimally small and we write: Acceleration is a vector with direction defined by and its units are length/(time x time): meters/sec/sec miles/hour/hour feet/sec/sec

/a v t and v t

v2/ secm

2/ secm 2/miles h2/ secf

a

/a v t

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can be orfinal initialv v v

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Distance Traveled in Straight line motion with Constant acceleration

http://www.physics.purdue.edu/class/applets/phe/acceleration.htm

Using integral calculus you can show that the distance “d” traveled during

time “t” is equal to the area under the velocity – time curve.

This area consists of the sum of a rectangle and a triangle

In terms of the x coordinate

0( )v t v at

2

0 02 2

t at atd v t v t

2

0 02

atx x v t

=at Area of triangle

2

at t

0Area v t

2

0

1

2d v t at

t

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Uniform Circular Motion

Acceleration occurs when the velocity changes in magnitude or direction or both.

The simplest example is the uniform circular motion.

In this case the magnitude of v does not change, only its direction.

Thus the acceleration vector points toward the center of the circle.

a

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Straight line motion

100 meter track event

d

a

t

t

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Velocity and acceleration

• •Remember v = Δd/Δt a = Δv/Δt •So the magnitude of a is not related to the magnitude of v and the direction of a is not related to the direction of v • v = 0 a = + accelerating from rest in the forward direction • v = 0 a = - reversing from rest, speed increasing backwards direction • v = + a = + increasing velocity, moving forward direction • v = + a = - decreasing velocity, moving forward direction • v = - a = + slowing down, moving backward direction • v = - a = - speeding up in the – x direction, moving backward direction

- + x d

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Graphs

For a specific journey even with variable acceleration one can determine everything about the journey, that is

as a function of time from

A distance versus time graph

Or

A velocity versus time graph (except the start point)

Or

An acceleration versus time plot (except the start velocity

or the start point)

( )x t

( )v t

( )a t

, ,d v a

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Summary Chapters 1 and 2

Units----Length, mass, time SI units m, kg, second

Coordinate systems:

Average speed = distance/time = d/t

Instantaneous speed = d/t

Vector quantities---magnitude and direction

Velocity----magnitude is speed

Acceleration = change in velocity/time =Δv/Δt

- + x d

v speed s

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One dimensional motion constant acceleration

v = v0 + at. Velocity changes by the amount “a” every second Eq.1

d = v0t + 1/2at2 d is the distance from the starting point at t =0 Eq.2

Rewrite Eq. 2 as . Using Eq.1 we can eliminate

and obtain for d

d = 1/2(v + v0) t Eq.3

Put t = 2d/ (v + v0) into Eq. 1 v = v0 + at

We obtain

v2 = v02 + 2ad Eq.4

There are only two independent equations

022

td v at

0at v v

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Questions Chapter 2

Q8 A car traveling around a circular track moves with

constant speed. Is this car moving with constant velocity

Q9 A ball is thrown against a wall and bounces back toward the

thrower with the same speed as it had before hitting the wall.

Does the velocity of the ball change in this process? Explain.

No, the direction is changing

Yes, it changes direction

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Q10 A ball attached to a string is whirled in a horizontal circle

such that it moves with constant speed.

a. Does the velocity of the ball change in this process?

Explain.

b. Is the acceleration of the ball equal to zero? Explain.

Q11 A ball tied to a string fastened at the other end to a rigid

support forms a pendulum. If we pull the ball to one side and

release it, the ball moves back and forth along an arc determined

by the string length.

A. Is the velocity constant in this process? Explain.

B. Is the speed likely to be constant in this process? What

happens to the speed when the ball reverses direction?

The velocity changes direction so there is acceleration

A Both magnitude and direction change.

B The speed is zero

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Q15 A car just starting up from a stop sign has zero velocity at the

instant that it starts. Must the acceleration of the car also be zero at

this instant? Explain.

Q17 A racing sports car traveling with a constant velocity of

100 MPH due west startles a turtle by the side of the road who

begins to move out of the way. Which of these two objects is

likely to have the larger acceleration at that instant? Explain.

The acceleration is not zero, if it was the car would not move

The car has zero acceleration but the turtle has acceleration

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Q18 In the graph shown here, velocity is plotted as a function of

time for an object traveling in a straight line.

A. Is the velocity constant for any time interval shown? Explain.

B. During which time interval shown does the object have the

greatest acceleration? Explain.

2 4 6 8 t (secs)

v

A Yes from 0 – 2 seconds B From 2 – 4 seconds

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Q19 A car moves along a straight line so that its position (distance

from some starting point) varies with time as described by the

graph shown here.

1. Does the car ever go backward? Explain.

2. Is the instantaneous velocity at point A greater or less than that

at point B? Explain.

Q20 For the car whose distance is plotted against time in Q19, is

the velocity constant during any time interval shown in the graph?

d

t

A

B

1 Yes in the last part

2 Greater at A

YES

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Q28 A car traveling in the forward direction experiences a

negative uniform acceleration for 10 seconds. Is the distance

covered during the first 5 seconds equal to, greater than, or less

than the distance covered during the second 5 seconds?

Explain.

If the car is always moving in the forward direction then it’s speed is

higher in the first 5 seconds so the distance covered is greater

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Ch 2 #8

Car travels with a speed of 25 m/s

What is the speed in km/s, km/h?

a) 1000 m = 1 km 25/1000 km/sec

= 0.025 km/s or 25x10-3 km/sec

b) 3600 s = 1 hour 1m = (1/1000)km

25 x 10-3 x 3600km/hr = 90km/h

- + x d

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Ch 2 #12

v0 = 30 m/s v = 18 m/s t = 4 sec

What is the average acceleration?

a = (18 – 30)/4 = -3 m/s/s = -3 m/s2

- + x d

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Ch 2 #14

v0 = 5 m/s a = 1.2 m/s2 t = 2 sec

What is the final velocity?

What distance is covered?

a) v = v0 +at = 7.4 m/s

b) d = v0t + ½ at2 = 12.4 m

- + x d

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Ch 2 #16

v0 = 9.0 m/s a = -1.5 m/s2 t = 2 sec

What is the final velocity?

What distance is traveled?

a) v = v0 + at = 6 m/s

b) d = v0t + ½ at2 = 15 m

- + x d

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Ch 2 CP4

v0 = 14 m/s a = 2 m/s2 v = 24m/s

What is the time?

What is the distance?

Computed at 1 second intervals.?

a) v = v0 + at t = 5s

b) d = v0t + ½ at2 = 95m

c) 1 sec = 15 2 sec = 32 3 sec = 51 m 4 sec = 72

- + x d