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Physics 214 Physics of everyday phenomena

Professor Suzanne Lorenz Office room PHYS 306 selorenz@purdue.edu

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

Announcements, Syllabus, schedule, Lecture notes, practice exams  Lists lecture schedule  Times and place of the two evening exams  Deadlines for Homework and Quizzes  Use of the I clicker  Useful information

Undergrad Office Room 144, Questions

This Week •  Introduction Syllabus, CHIP, Office hours •  Grading Exams, I clicker, pre lecture quiz •  General Who am I, our Universe •  Lecture Ch 1,2 Straight line motion •  Tsunamis

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The Book

 Book : Physics of Everyday Phenomena 5th, 6th or 7th edition

 OVERVIEW  OUTLINE  CHAPTER MATERIAL  SUMMARY  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

  I encourage interaction and will leave plenty of time for questions.

 There will be two one hour evening exams and a two hour final

 We will be using I clickers for in class quizzes

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Reading and Problems

It is very important that you  Read all the chapter material  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 noon Friday Jan 17th There are 32 pre lecture quizzes First one is due by 8.30am Wed Jan 15th

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 three levels of help •  See me during office hours in room 306 Physics •  Mon 2:30 – 4:00pm or By appointment •  Send questions by email to selorenz@purdue.edu •  see me quickly after lecture to make an appointment Exams Exam 1 Feb 13th 8 – 9pm Phys Room 112 Exam 2 April 3rd 8 – 9pm Phys room 112

There will be a 2 hour evening help session before each exam. Feb 11th 7 – 9pm and April 1st 7 – 9pm

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Plus Minus Grading

A+,A 4.0

A- 3.7

B+ 3.3

B 3.0

B- 2.7

C+ 2.3 C 2.0 C- 1.7 D+ 1.3 D 1.0 D- 0.7 E, F, WF, EF, IF 0.0

We will be using the Plus Minus grading system

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Who am I Originally from Kentucky-Undergraduate degree from

University of Louisville-PhD from Purdue. Thesis: Dark Matter Mapping. Current work: Dark Matter Indirect Detection

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Dark Matter

VERITAS

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This week

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•  Our Universe •  Our World •  How do we measure quantities •  Describing moving objects •  Tsunami’s

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What is Physics

Physics is the study and understanding of all the physical phenomena

 That we see in our everyday life  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 – Hubble, Cobe, WMAP  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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Experiment and theory

 Our knowledge is based on experiments which are reproducible.   We develop mathematical theories which agree with experiment and generally predict new phenomena.  Experimentalists are not constrained by the theory and continue to examine our Universe from 10-17m to 13 billion light years and from t = “0” to 13.7 billion years later.  any new theory must agree with all previous experimental observations.  A theory is a mathematical consistent framework for the interpretation of all accumulated knowledge.  It is like looking at a partially painted picture and determining what the finished picture would depict.

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Physics of the Universe

 We only have one planet  We only have one Universe  Current understanding is always based on the simplest explanation that fits the facts (no aliens!!)  Experimental measurements always have errors  Forefront science is very difficult and incorrect results do occur which are then corrected

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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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Framework Underlying principles  Physics is the same everywhere  Fundamental constants and physical laws have not changed over the age of the Universe Observations  We can create conditions in the lab which existed a billionth of a second after the big bang.  We can understand how our Universe evolved over 13 billion years and actually observe the evolution of the Universe

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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  Strong Force – holds the protons and neutrons of the

nucleus together  Weak Force – responsible for radioactive decay  Electromagnetic force – Holds electrons in atoms,

electrical currents, magnetism, light  Gravitation - Attractive force between objects, solar

system  Dark Energy – mysterious force expanding space

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Structure and Forces Gravitation Solar system galaxies objects falling Electric charge everything not gravity

biology photosynthesis

cars, planes

F

F

F

F

Strong Force

+ electron Neutron Proton

Weak Force

Common carrier of electric charge and electric current is the electron

Radioactive decay

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Building blocks Building blocks Quarks – up, down, strange, charm, beauty,top Leptons - electron, muon, tau, 3 neutrinos Force carriers – γ, g, W, Z

Missing pieces Building blocks – Higgs, supersymmetry… Questions – Dark energy, dark matter….. Speculation – parallel universes, extra dimensions..

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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. As we go through the semester I will discuss and explain everyday physics topics.

I encourage you to ask questions on any topic or send me an email with your question and I’ll answer and also discuss the topic in class if it is of general interest

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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  Length (distance)  Time  Coordinate system (reference point, direction, clock)  Mass ( so much of something)

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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 0.001

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 interval s = d/Δt We can plot speed versus time and obtain a graph which has all the information for the journey moviecar

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Vector quantities In addition to knowing average speed or instantaneous speed we need to know the direction. The quantity giving 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.

To specify direction we need a coordinate system

Velocity

Acceleration Force momentum

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. We will use coordinate systems in one or two dimensions

+ +

-

-

- + x

x

y N

W

S

E

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The earth as a coordinate system and Maps

1 nautical mile = 1/21600 of the circumference of the earth at the equator 1 knot = 1 nautical mile per hour 1.1508 miles/hour 1 kilometer = 1/10,000 the distance from the North Pole to the equator passing through Paris

We live on a sphere but most maps are flat and this increases the apparent size of countries as one moves further from the equator

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Motion in a straight line

d is the distance from the start point it is NOT necessarily the total distance traveled

1 Constant velocity + 2 Stopped 3 Constant velocity + 4 Constant velocity -

1 2 3 4

- + x d

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Acceleration A change in velocity is called acceleration a = change in velocity/elapsed time a = Δv/t Average acceleration t is “large” Instantaneous acceleration a = Δv/ Δt Acceleration is a vector with direction defined by Δv units are length/(time x time) meters/sec/sec miles/hour/hour feet/sec/sec

Δv = vfinal – vinitial can be + or –

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Straight line motion Constant acceleration

v = v0 + at (definition of acceleration) “red area” = vΔt = distance traveled in Δt d = v0t + 1/2 Δv t but since a = Δv/t d = v0t + 1/2at2 (d is distance from start)

or d = 1/2(v + v0) t (average speed times t)

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

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General case of acceleration

Acceleration occurs when the velocity changes in magnitude or direction or both. In the first example shown if the magnitude of v does not change we have uniform circular motion and the acceleration vector points toward the center of the circle.

a

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Straight line motion

d

a

100 meter track event

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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 v = 0 a = - reversing from rest (speed increasing) v = + a = + increasing velocity v = + a = - decreasing velocity v = - a = + slowing down v = - a = - speeding up in the – x 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 d,v,a 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)

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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/Δt Vector quantities---magnitude and direction Velocity----magnitude is speed Acceleration = change in velocity/time =Δv/Δt

- + x d

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One dimensional motion constant acceleration

1) v = v0 + at velocity changes by the amount a every second

2) d = v0t + 1/2at2 d is the distance from the start point at t = 0

3) d = 1/2(v + v0) t 1/2(v + v0) is the average velocity

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

4) v2 = v02 + 2ad

There are only two independent equations

Drag race v0 = 0 v = 2d/t

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Tsunami To put the recent Tsumami in perspective we can look at the evolution of the earth for the last 250 million years

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Current plate movements

Notice the position of the Indian Subcontinent today. It moved hundreds of miles in 135 million years at a great speed (4 inches per year!!!) The Indian plate crashed into the Eurasian plate with such speed and force that it created the tallest mountain range on Earth, the Himalayas

http://www.scotese.com/futanima.htm

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Origin and Destruction

tsunami.mov

A massive change in the sea floor maybe over hundreds or a thousand miles displaces a very large volume of water and generates strong disturbances as the water tries to reach equilibrium As the tsunami crosses the deep ocean, its length from crest to crest may be a hundred miles or more, and its height from crest to trough will only be a few feet or less. They can not be felt aboard ships nor can they be seen from the air in the open ocean. In the deepest oceans, the waves will reach speeds exceeding 600 miles per hour (970 km/hr). When the tsunami enters the shoaling water of coastlines in its path, the velocity of its waves diminishes and the wave height increases. It is in these shallow waters that a large tsunami can crest to heights exceeding 100 feet (30 m) and strike with devastating force.

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Mega Tsunami’s

Around the world there are accumulations of material from the ocean floor called chevrons that could have been deposited by giant waves after a meteorite impact. Some of these have been linked to impact craters on the ocean floor. Such waves would have been 1000 feet high!!

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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