Download Physics 214 Physics of everyday phenomena

Physics 214
Physics of everyday phenomena
Professor Laszlo J. Gutay
Office room 314
[email protected]
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
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This Week
•
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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
E=mc2
Energy density is the same as a billionth
of a second after the Big Bang
which produced the building blocks of
our Universe
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Higgs Boson
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
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This week
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
F
3. Strong Force
Solar system
galaxies
falling objects
2. Electric charge
F
everything not gravity
F
biology
F
4. Weak Force
photosynthesis
+ electron
cars, planes
The basic carrier of electric charge
and electric current is the electron
(Franklin)
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Neutron
Proton
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
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Observation and Everyday life
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
1 in
2.54cm
mega
1,000,000
106
million
1cm
0.394in
kilo
1,000
103
thousand
1ft
30.5cm
centi
1/100
10-
hundredth
1m
39.4in
thousandth
1km
0.621mi
1mi
5280ft
1.609km
1lb
0.4536kg
g =9.8
1kg
2.205lbs
g=9.8
0.01
3.281ft
2
milli
micro
1/1000
0.00
1
1/1,000,000
1/106
103
10-
millionth
6
nano
1/1,000,000,000
1/109
109
billionth
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:
Velocity:
v
Acceleration:
Force: F
Momentum: p
a
To specify direction of a vector we need a coordinate system.
Further details in the textbook see Appendix c
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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.

+
N
W
y +
E
-
X
Origin
x=0, y=0
+
x
-
S
This was invented by Descartes. Cartesian is the Latin translation of his name
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Motion in a straight line along the X axis
-
+ x
d
0 starting point
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 x  vt ,if it started from origin at t  0
2
3
4
1
x  vt  x0 , if it started from x0 at t  0
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Acceleration
A change in velocity is called acceleration a.
If the increase of the time of the average acceleration t is “large”,
we write: a  v / t .
Incase of instantaneous acceleration both v and t
are infinitesimally small and we write: a  v / t
Acceleration is a vector with direction defined by v
and its units are length/(time x time): m / sec 2
meters/sec/sec miles/hour/hour feet/sec/sec
m / sec 2
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f / sec 2
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v  v final  vinitial
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can be  or 
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Distance Traveled in Straight line motion
with Constant acceleration
Using integral calculus you can show that the distance “d” traveled during
time “t” is equal to the area under the velocity – time v(t )  v0  at curve.
This area consists of the sum of a rectangle and a triangle
t  at
at 2
d  v0  t 
 v0t 
2
2
In terms of the x coordinate
=at
at 2
x  x0  v0t 
2
Area of triangle 
at  t
2
Area  v0t
1
d  v0t  at 2
2
t
http://www.physics.purdue.edu/class/applets/phe/acceleration.htm
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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
t
a
t
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Velocity and acceleration
-
d
+ x
•
•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
v=0
v=+
v=+
v=v=-
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a=+
a=a=+
a=a=+
a=-
accelerating from rest in the forward direction
reversing from rest, speed increasing backwards direction
increasing velocity, moving forward direction
decreasing velocity, moving forward direction
slowing down, moving backward direction
speeding up in the – x direction, moving backward direction
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Graphs
For a specific journey even with variable acceleration one
can determine everything about the journey, that is d , v, a
as a function of time from
A distance versus time graph  x(t )
Or
A velocity versus time graph (except the start point)  v(t )
Or
An acceleration versus time plot (except the start velocity
or the start point)  a(t )
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Summary Chapters 1 and 2
-
d
+ x
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 v  speed  s
Acceleration = change in velocity/time =Δv/Δt
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One dimensional motion constant acceleration
v = v0 + at. Velocity changes by the amount “a” every second
d = v0t + 1/2at2 d is the distance from the starting point at t =0
t
Rewrite Eq. 2 as d   2v0  at . Using Eq.1 we can eliminate at  v  v0
and obtain for d
Eq.1
Eq.2
2
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
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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
No, the direction is changing
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.
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.
The velocity changes direction so there is acceleration
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?
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.
The acceleration is not zero, if it was the car would not move
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 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.
v
2
4
6
8
t (secs)
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.
1 Yes in the last part
2 Greater at A
d
B
A
t
Q20 For the car whose distance is plotted against time in Q19, is
the velocity constant during any time interval shown in the graph?
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
-
d
+ x
Car travels with a speed of 25 m/s
What is the speed in km/s, km/h?
a) 1000 m = 1 km
= 0.025 km/s
25/1000 km/sec
or
25x10-3 km/sec
b) 3600 s = 1 hour 1m = (1/1000)km
25 x 10-3 x 3600km/hr = 90km/h
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Ch 2 #12
-
d
+ x
v0 = 30 m/s
v = 18 m/s
t = 4 sec
What is the average acceleration?
a = (18 – 30)/4
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= -3 m/s/s = -3 m/s2
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Ch 2 #14
-
d
v0 = 5 m/s
a = 1.2 m/s2
What is the final velocity?
What distance is covered?
+ x
t = 2 sec
a) v = v0 +at = 7.4 m/s
b)
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d = v0t + ½ at2 = 12.4 m
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Ch 2 #16
-
d
v0 = 9.0 m/s
a = -1.5 m/s2
What is the final velocity?
What distance is traveled?
+ x
t = 2 sec
a) v = v0 + at = 6 m/s
b) d = v0t + ½ at2 = 15 m
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Ch 2 CP4
-
d
+ x
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
c) 1 sec = 15
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= 95m
2 sec = 32
3 sec = 51 m
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4 sec = 72
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