Physics 1201W: Lecture 1

1
Physics 1201W Lecture 1Intro. Physics for
Life Science Students

• Introduction
• Course Information
• Measurement and Units Vectors (Chapter 1)
• Assignments for week

2
Who am I?

• Prof. James Kakalios
• Contact info on web page
• easiest to find me
• before or after class in Rm 150
• at office hours
• I DO NOT ANSWER EMAIL FOR THIS CLASS.
• We will designate one TA to answer business
  e-mail.
• I do research in Experimental Condensed Matter
  Physics, primarily on amorphous semiconductors
  for solar cell applications, granular media and
  voltage fluctuations in the brain
• Ive written a popular science book The Physics
  of Superheroes

3
Amorphous Silicon Solar Cells
PECVD Amorphous Silicon

• Advantages
• Large area uniform deposition
• Completely fabricated bythin film technology
• Strong absorption in visible light
• Inexpensive!

4
1/f noise characteristic of complex, messy systems

• Metal, semiconducting resistors
• Spin Glasses
• Sunspot activity
• X-ray emissions from Cygnus X-1
• Flood levels of the Nile
• Traffic Jams

Khera and JK, Phys Rev B 56 (1997)
5
Properties of Granular Media
Courtesy of Heinrich Jaegers Lab
6
Axial Segregation
7
Does Axial Segregation Depend on Spherical
Particles?
8
Does Axial Segregation Depend on Spherical
Particles? NO!
9
(No Transcript)
10
Who are you?

• Hi, My name is _________________________. I
  am a ______________ major.
  The thing I most want to learn from this Physics
  class is ______________.

11
Course Information

• See info on the Web
• www.physics.umn.edu and follow courses link to
  the Physics 1201W.100 homepage
• Office hours contact info
• Syllabus, Links, Announcements
• The schedule and the recommended homework
  problems are on the web page.
• Course has several components
• Lecture (slides, demos, examples of problem
  solving, conceptual problems, responses graded)
• Homework (Problems in book Solutions on-line)
• Labs (group exploration of physical phenomena)
• Recitations (group practice of problem solving)
• Tests (4 Quizzes, 1 Final)

12
Necessary Books Tools All are available at
the Bookstore

• Serway Jewett Principles of Physics 3rd
  Edition
• Physics Laboratory Manual for Physics 1201
• Laboratory journal University of Minnesota
  2077-S
• Electronic Response Transmitter
• Simple Scientific Calculator
• In addition you may want to get a brief calculus
  reference such as
• Ayres/Mendelson Schaum's easy outlines Calculus
• Morgan Calculus Lite
• Thompson Calculus Made Easy.

13
(No Transcript)
14
(No Transcript)
15
Lecture Organization

• Three main components
• Lecturer discusses class material
• As many demos as possible
• If you see it, you have to believe it!
• Students work in groups on conceptual problems
• Several per lecture, sometimes graded

16
WARNING YOU MUST PASS LAB!

• In order to pass this class, you must get 60 or
  better on the lab component.
• There are no make-up labs except in situations
  officially recognized by the University. In that
  case, the laboratory work must be made up by
  arrangement with your lab instructor before your
  next scheduled laboratory period.
• Grades for the laboratory work will be determined
  in part by laboratory reports (one for each
  laboratory topic), in part by your work in the
  laboratory, in part by a final laboratory exam,
  and in part by your prediction and methods
  questions turned in before lab.

17
It is important to keep up on the reading,
homework and lab work

• In order to cover the material that the College
  of Biological Sciences wants students to know, we
  cover a lot of material. It is important for you
  to keep up.
• If you find you are having difficulties doing the
  homework problems, take a look at The Competent
  Problem Solver, available in the bookstore.
• Even though HW is not graded, you should do all
  suggested problems. At least one will appear on
  the relevant quiz.

18
QUIZ and Final Schedule
Quizzes are tentatively scheduled on
Feb. 8, Mar. 10, Apr. 4 and Apr. 25
and in recitation the preceding Thursday.
FINAL Friday, May 16th from 130 430 pm
19

Course grade The course grade will be determined
by combining the grades from the various
components of the course in the following two
ways - or - 45 Sum of three best
quizzes 55 All four quizzes 15 Laboratory
work 15 Laboratory work 35 Final
exam 25 Final exam 5 Clicker
Questions 5 Clicker Questions
20
This week in lab and recitation

• Recitation
• Get your personal response system registered with
  TA
• Do a group problem
• Lab
• Diagnostic tests
• The Force Diagnostic is a test of your physics
  intuition about forces and motion.
• The Math diagnostic is a test of the math skills
  you are likely to need in this class
• Intro to the lab software, etc.

21
What is Physics?

• The quantitative study of the natural world (laws
  methods)
• The foundation of Chemistry, Biology,
  Engineering, etc.
• A predictive method for inanimate objects
• The process of seeking and applying knowledge
  the body of that knowledge
• Study of fundamental structure and interactions
  at a various length scales

22
Physics does NOT

• Require an encyclopedic knowledge of facts and
  equations
• The ability to do complex calculations in your
  head with robotic speed and precision
• Physics does not require that we have all the
  answers
• But Physics does involve asking the right
  questions!

23
How many piano tuners work in the Twin Cities?
2x106 people in the cities 1/10 families have
a piano 4 people / family
pianos (1/10) pianos/family x (1/4)
families/person x 2 x 106 persons/Twin Cities
5 x 104 pianos/Twin Cities
Need to tune each piano once a year.
24
How many piano tuners work in the Twin Cities?
So 5 x 104 tunings/year. Each tuning takes 2
hours
5 x 104 piano tunings/year 50
Tuners 103 piano tunings/year/Tuner
I find 56 tuners listed in the Minneapolis Yellow
Pages
25
Our approach to physics

• Look at a simpler object and interaction
• How can we describe the interaction?
• My hand pushes the cart (applies a force)
• My hand transfers energy to the cart

26
Mechanics

• One obvious change in the state of an object is
  motion
• What causes objects to move or allows them to be
  stationary?
• We must understand how to describe motion.
• statics - bodies in equilibrium
• dynamics - explanation of motion in terms of
  forces
• energy -explanation of motion in terms of
  conservation of energy
• Energy and thermodynamics

27
Units

• How we measure things!
• All things in classical mechanics can be
• expressed in terms of the fundamental units
• Length L
• Mass M
• Time T
• For example
• Speed has units of L / T (i.e. miles per hour).
• Force has units of ML / T2 etc... (as you will
  learn).

28
Système International d'Unité
Is it a coincidence that in modern units the
circumference of the earth is 40,000 km?

• No, in 1795 the meter was defined this way in
  Paris
• 1 kg weight of 1000 cm3 pure H2O at
  0C.
• 0 C melting point of ice
• freezing point of H2O.
• 100 C Boiling point of H2O
• First real international standards

29
Standard Mass
Platinum-iridium standard kg
30
Mass

• How much Matter
• SI unit is the kilogram kg.
• Compare to standard kg in Paris
• English unit is the slug
• Measure of resistance to acceleration
• is called inertia
• Mass ¹ Weight
• Weight is caused by gravity and is a force
• A 1 kg mass weighs 2.2 lb on the earth.

31
SI Units

• Physics is a quantitative science, so units and
  accuracy are very important. National Institute
  of Standards and Technology (NIST) keeps
  standards and provides calibration services.
• We will use primarily SI units in this course.
• Most countries (including England) use the metric
  system.
• In the US we use the "English" system, and are
  slowly converting to metric (cost is staggering).
• We will see that metric is simpler and more
  logical.
• SI system will make unit analysis simpler.

32
Length

• Distance Length (m)
• Radius of visible universe 1 x 1026
• To Andromeda Galaxy 2 x 1022
• To nearest star 4 x 1016
• Earth to Sun 1.5 x 1011
• Radius of Earth 6.4 x 106
• Football field 1.0 x 102
• Tall person 2 x 100
• Thickness of paper 1 x 10-4
• Wavelength of blue light 4 x 10-7
• Diameter of hydrogen atom 1 x 10-10
• Diameter of proton 1 x 10-15

33
Time

• Interval Time (s)
• Age of universe 5 x 1017
• Age of Grand Canyon 3 x 1014
• 32 years 1 x 109
• One year 3.2 x 107
• One hour 3.6 x 103
• Light travel from Earth to Moon 1.3 x 100
• One cycle of guitar A string 2 x 10-3
• One cycle of FM radio wave 6 x 10-8

UIUC
34
Mass

• Object Mass (kg)
• Milky Way Galaxy 4 x 1041
• Sun 2 x 1030
• Earth 6 x 1024
• Boeing 747 4 x 105
• Car 1 x 103
• Student 7 x 101
• Dust particle 1 x 10-9
• Proton 2 x 10-27
• Electron 9 x 10-31

UIUC
35
Units

• SI (Système International) Units
• MKS
• L meters (m)
• M kilograms (kg)
• T seconds (s)
• British Units
• Inches, feet, miles, pounds, slugs...
• We will use mostly SI units, but you may run
  across some problems using British units. You
  should know how to convert back forth.

36
Converting between different systems of units

• Useful Conversion factors
• 1 inch 2.54 cm
• 1 m 3.28 ft
• 1 mile 5280 ft
• 1 mile 1.61 km
• Example convert miles per hour to meters per
  second

37
Unit Conversion
I am walking at 5 mph. How fast in m/s? Using
1.00 mi 1.61 km and 1 hour 3600 sec
Alternatively if we know that 1 mph .447 m/s
38
Dimensional Analysis

• This is a very important tool to check your work
• Its also very easy!
• Example
• Doing a problem you get the answer
• distance d vt 2 (velocity x time2)
• Units on left side L
• Units on right side L / T x T2 L x T
• Left units and right units dont match, so answer
  must be wrong!!

UIUC
39
Significant Figures

• Use appropriate accuracy, usually set by accuracy
  of given information
• digits indicates accuracy
• Scientific notation
• 6.12 x 105 has 3 sig figs, 612000 has 6

2 sig figs vs 6 sig figs 10 m vs
10.0000 m 9.7 m vs 9.71345 m
Examples 1.7 g salt is added to 3.4 g
salt. How much total? 1.7 g 3.4 g 5.1 g
2 sig figs 100 0.02 100 10 x 6.123
61
40
Estimation

• Order of magnitude or rough calculation
• Use physical insight to estimate unknown
  quantities
• Keep only one significant figure during
  calculation.
• Thus use 2 x 102 or 200 , but not 243
• Example How many piano tuners work in the Twin
  Cities?

41
CT Dimensional Analysis

• The period P of a swinging pendulum depends only
  on the length of the pendulum d and the
  acceleration of gravity g.
• Which of the following formulas for the period P
  could be correct ?

Length d has units of length (L) Acceleration g
has units of (L / T 2) Period P has units of time
(T )
UIUC
42
CT 1 Solution

• Try the first equation

T ? (LL/T2)2L4/T4
43
CT 1 Solution

• Try the second equation

44
CT 1 Solution
Try the third equation
45
Coordinate Systems

• Used to describe the position of a point in space
• Coordinate system consists of
• A fixed reference point called the origin
• Specific axes with scales and labels
• Instructions on how to label a point relative to
  the origin and the axes

46
Cartesian Coordinate System

• Also called rectangular coordinate system
• x- and y- axes intersect at the origin
• Points are labeled (x,y)

47
Polar Coordinate System

• Origin and reference line are noted
• Point is distance r from the origin in the
  direction of angle ?, counter-clockwise from
  reference line
• Points are labeled (r,?)

48
Polar to Cartesian Coordinates

• Based on forming a right triangle from r and q
• x r cos q
• y r sin q

49
Cartesian to Polar Coordinates

• r is the hypotenuse and q an angle
• q must be ccw from positive x axis for these
  equations to be valid

50
Scalars and vectors

• Constant Scalar A simple number, has magnitude
  and units
• Scalar function f (x,t)

Example Density of students in room 150
51
Vectors

• In 1 dimension, we could specify direction with a
  or - sign. For example, an object moving to
  the left (-) or right ().
• In 2 or 3 dimensions, we need more than a sign to
  specify the direction of something
• To illustrate this, consider the position vector
  r in 2 dimensions.

52
Vectors

• Example Where is Duluth?
• Choose origin at Minneapolis
• Choose coordinates of distance (miles), and
  direction (N,S,E,W)
• In this case r is a vector that points 120
  miles north.

53
2d coordinate system
54
2d coordinate system
55
Displacement vector
56
Vectors

• There are two common ways of indicating that
  something is a vector quantity
• Boldface notation A
• Arrow notation

A
57

• The components of r are its (x,y,z) coordinates
• r (rx ,ry ,rz ) (x,y,z)
• NOTE We must choose an origin and a coordinate
  system
• Consider this in 2-D (since its easier to draw)
• rx x r cos ???
• ry y r sin ???

(x,y)
y
????arctan( y / x )
r
where r r
?
x
58
Warning

• The component equations (Ax A cos q and Ay A
  sin q) apply only when the angle is measured with
  respect to the x-axis (ccw from the positive
  x-axis).
• The resultant angle (tan q Ay / Ax) gives the
  angle with respect to the x-axis.
• You can always think about the actual triangle
  being formed and what angle you know and apply
  the appropriate trig functions

59
Vectors

• The magnitude (length) of r is found using the
  Pythagorean theorem

• The length of a vector clearly does not depend on
  its direction.

60
Calculating the angle if we know the components
61
Vector Addition

• Consider the vectors A and B. Find A B.

• We can arrange the vectors as we want, as long as
  we maintain their length and direction!!

62
Adding Vectors Graphically, cont.

• Continue drawing the vectors tip-to-tail
• The resultant is drawn from the origin of to
  the end of the last vector
• Measure the length of and its angle
• Use the scale factor to convert length to actual
  magnitude

63
Adding Vectors Graphically, final

• When you have many vectors, just keep repeating
  the process until all are included
• The resultant is still drawn from the origin of
  the first vector to the end of the last vector

64
Adding Vectors, Commutative Property of Addition

• When two vectors are added, the sum is
  independent of the order of the addition, i.e.
  vector addition is commutative.

65
Adding Vectors, Associative Property of Addition

• When adding three or more vectors, their sum is
  independent of the way in which the individual
  vectors are grouped

66

• When adding vectors, all of the vectors must have
  the same units.
• All of the vectors must be of the same type of
  quantity. For example, you cannot add a
  displacement to a velocity

67
Negative of a Vector

• The negative of a vector is defined as the vector
  that, when added to the original vector, gives a
  resultant of zero
• Represented as
• The negative of the vector will have the same
  magnitude, but point in the opposite direction

68
Subtracting Vectors

• Special case of vector addition
• Continue with standard vector addition procedure

69
Multiplying or Dividing a Vector by a Scalar

• The result of the multiplication or division is a
  vector
• The magnitude of the vector is multiplied or
  divided by the scalar
• If the scalar is positive, the direction of the
  result is the same as of the original vector
• If the scalar is negative, the direction of the
  result is opposite that of the original vector

70
Unit Vectors

• A Unit Vector is a vector having length 1 and no
  units
• It is used to specify a direction
• Unit vector u points in the direction of U
• Often denoted with a hat u û

• Useful examples are the Cartesian unit vectors
  i, j, k
• directions of the x, y and z axes

71
Unit Vectors

• Useful examples are the Cartesian unit vectors
  i, j, k
• directions of the x, y and z axes

72

• We can write the vector in terms of its
  components along the unit vectors.

73
Vector addition using components

• Consider C A B.

(a) A B (Ax i Ay j) (Bx i By j)
(Ax Bx)i (Ay
By)j (b) C Cx i Cy j

• Comparing components of (a) and (b)
• Cx Ax Bx
• Cy Ay By

74
Adding Vectors

• Vector A (0, 2, 1)
• Vector B (3, 0, 2)
• Vector C (1, -4, 2)

What is the resultant vector, D ABC ?
(a) (3,5,-1) (b) (4,-2,5) (c) (5,-2,4)
UIUC
75
Adding Vectors

• Vector A (0, 2, 1)
• Vector B (3, 0, 2)
• Vector C (1, 4, 2)

D (AX BX CX)i (AY BY CY)j (AZ BZ
CZ)k (0 3 1) , (2 0 - 4) , (1
2 2) 4,-2,5 Choice (b)
UIUC
76
Physics 1201 Reading HW Assignment

• Before next Monday
• Do Text Problems from Chapters 1
• (for sections we have covered)
• Read Text Chapter 2
• By lab next week
• Read Lab 1 and do predictions and methods
  questions