modern physics 2009     trimester 3

Serway's Chapter 16 (on-line only) on Cosmology

course expectations   &   syllabus
   
 
Monday,
March 30
Tuesday,
March 31
Wednesday,
April 1
Thursday,
April 2
Friday,
April 3
class
 
 
 
 

very short reading quiz due by 1 pm today.....

now available on moodle

if you are missing today's class for a prearranged absence, the quiz must be submitted by 8 pm Sunday

quiz next tuesday or wednesday ?? (we're waiting on votes from david and haoyang) on chapters 1 and 2 
what we'll do
in class
more relativistic dynamics
finish chapter 2

last chance to practice Lorentz transformations and mass/energy stuff:

problem 1(23)

the faster-than-light jets observed in quasars....

at what speed (v/c) will the mistake we make by using the non-relativistic formula for KE be larger than 1%?

start nuclear physics
reading
(always done
before class)

1st pages of chapter 2, pp. 41-43

fill in the 3 rows & columns we had on the board friday:


formula learned
in intro physics
relativistic formula in frame in
which object is at rest
relativistic formula in frame
in which object
is moving
force



momentum



work



 
  1st pages of chapter 2, pp. 41-43

+

examples on page 44

+

examples on page 49,
especially example 6
 
 
 13(1 up through/including example 2)

13(2 up through/including example 3)

then submit reading quiz above in moodle
in-class
presentation





written
homework
(by 5 pm)
write the LT equations
1(23) and 1(26) as a matrix equation of the form

a x-bar
    (                  )   =
b ct-bar

                   ax
     [L(v/c) ]  (          )
                      b ct

where

ax
(             )
b ct

represents a vector matrix of event coordinates in one frame

and

L(v/c)

is a 2x2-matrix that represents the operation that
transforms the event coordinates (x, ct) in frame S
to event coordinates (x-bar, ct-bar) in frame S-bar
bring to class:

problem 1(20)

also,
<-----






















2(12, 15)

so you remember the formula for electic energy?

do you remember how to start a conservation of energy problem?
ask if you're not sure
 
rocket and earth problem
(wherein you are encouraged to do as many LTs as possible; however, each part can also be done as a
length contraction,
OR
time dilation
OR
time-lapse problem
(a la Tonya & Reid)
lab
 
 
 
alpha sources arrived yesterday, but since the prelab is lengthy, we will wait till next week

you can start the prelab this weekend!
 
other
 
do some problems out of chapter 2 on mass, kinetic energy, and total energy for practice
 
 


 
 
Monday,
March 23
Tuesday,
March 24
Wednesday,
March 25
Thursday,
March 26
Friday,
March 27
class
only teachers have classes 
bring your green sheet
(rotated reference frames) to class
(those who didnt have it quite right last Friday, please fix it for class today).... each coordinate in the rotated frame (x-bar-p, y-bar-p) should be a linear combination of the coordinates (xp, yp) in the original frame
[combine your terms; there should be no denominators, and no trig fucntions multiplying other trig functions]
 
 no lab today due to lack of alpha sources

bring to class TODAY:
given a 2x2 matrix M with the elements
a     b
c     d

find the elements of the inverse matrix
M-1,
such that
M M-1  = 
M-1 M  =
the identity matrix:
1     0
0     1
for monday:

write the LT equations
1(23) and 1(26) as a matrix equation of the form

a x-bar
    (                  )   =
b ct-bar

                  ax
     [L(vc) ]  (          )
                     b ct

where

ax
(             )
b ct

represents a vector matrix of event coordinates in one frame

and

L(v/c)

is a 2x2-matrix that represents the operation that
transforms the event coordinates (x, ct) in frame S
to event coordinates  (x-bar, ct-bar) in frame S-bar


what we'll do
in class


make progress toward understanding why the distance from the origin of any point is the same in both reference frames
more about the rotation matrix
R(q)....

if we define v to be the matrix vector containing the   coordinates, then

v-bar =  R(q) v
represents the matrix transformation of coordinates that we wrote down in class  yesterday

show how the Lorentz transformations include both time dilation and length contraction principles that we have learned


learn how to do velocity tranformation problems properly

finally learn what it is that makes the distance between any two points in the x-y plane absolute (and independent of choice of coordinate system)

[and of course what makes the "interval":

the same in all inertial reference frames



reading
(always done
before class)
sometime this week:

section 1(7), an alternative derivation of the invariance of "the interval"

section 1(3): how the Michelson-Morley experiment proved that the speed of light is the same for all observers

 
ALL of section 1(6):
this is a change from what I said in class on Tuesday
this might be a good time to do the reading in Monday's box
<------
 pp. 46-47

what are the new correct formulas for kinetic energy,
total energy of
particles "with mass" and particle without "rest mass" ?
in-class
presentation

do you have one for this week?

you don't have to make up your own! there are plenty in the back of chapter 1 !!



written
homework
(by 5 pm)


the rocket/earth twin paradox video clip:
find v/c by two different methods:

1) a time dilation problem

2) a doppler shift problem
(make sure that you let me know who has the flasher in your doppler problem)
following postponed till next week

prelab for  lab E2
due at beginning of class
(lab)

web site for finding daughters,
half-lifes, etc
(type the nucleus you're interested in inside the box at upper left corner; for example if you want info about carbon-12,
type C12)
 1(14, 28)

please do 28b as a length contraction problem
lab
 
 
 

we do
lab E2
IF the alpha sources from last year are still viable

lab E1 due 
other
 

have a presentation problem ready for today or this week?


what IS the cause of the redshifts of galaxies?
unfortunately, Serway's Chapter 16 on Cosmology (on line only) is equally bad at explaining the true reason for galaxies' redshifts [see for example equation 16.1 # equations 16.6 - 16.8 ---- although at least these contradict his incorrect equation 1.15 !!!!]

he actually has the correct reason in equations 16.11 & 16.22 but he doesn't draw attention to them at all & they are spaced far apart in the text

otherwise, chapter 16 is pretty well written and a nice summary of the evidence for the Big Bang & dark energy
 
 


   
 
Monday,
March 16
Tuesday,
March 17
Wednesday,
March 18
Thursday,
March 19
Friday,
march 20
class
 
 
 
you'll need a calculator that has the statistics package and on which you know how to find the mean and the standard deviation of a list of numbers in your statlist
(i.e. read your manual!!!)

you'll also need a lab book for lab today.... it does NOT have to be a new one; one you used in a previous course will do
bring green sheet (on coordinate transformations) completed to class 
what we'll do
in class
start the muon problem
finish the muon problem & come up with a procedure for length- contraction problems




lab E1
(link below, but I will provide copies)



Doppler effect

doppler effect applet
reading
(always done
before class)
 length contraction:
pp. 16-20

(also, I forgot to ask if you had questions about the invariance of  perpendicular-length handout)
no new reading, BUT.....

given the muon problem that we started in class yesterday:

consider the cloud-ground distance (defined by those 2 endpoints)....

you know (from class) that we want to make that distance largest from the earth frame ....

so what question can we ask (analagous to the one for time dilation: which observer says both events occurred at the same coordinates?) about the two endpoints such that the answer is the earth frame?   bring a question that satisfies the above conditions to class today
bring to class:

re-look at the table we created for the muon-earth problem....

and decide which things in the table are "exact" (in the sense that we defined them, so that they have an infinite number of 0's after the decimal)
and which things are only
"approximate" in the sense that we calculated them by approximating
v/c as 1

if we actually re-calculate these quantities, using v/c = 0.999949999
(instead of v/c = 1),
does the quantity 
Dx2 -  c2Dt2

become the same in both frames?























 
 














pp. 533-534, on how a Geiger Counter works

(the first couple pages of 13(4) and all of 13(6) might help you answer some of the lab questions if you are culturally illiterate




























pp. 21 through 26  on the twins paradox  and the Doppler effect






























in-class
presentation





written
homework
(by 5 pm)
1(8)
wrong problem
1(12),
the heartbeat problem

make sure you turn this into a time dilation problem 
this isn't an easy one.... start early,
in case you need to come and get help

the return of Tonya and Reid:
now Tonya stands at the back of the train, where the light also is...
consider the two events"
1) light leaves the back of the train
2) light returns to the back of the train

Since you know the time between the two events according to Tonya, you can do a time dilation problem to find the time interval according to Reid;
but Reid can also solve the problem by doing a d-v-a-t, even though he doesnt initially know the length of the train, according to him.  By equating the two method's answers, show that the train length according to Reid is g (gamma) times smaller than the length of train according to Tonya

use the applet at the following directory path:

T:\Student\kolena\Relativity_Physlets\
contents\s_relativity\sp_rel\section2_4.html

OR use this link in a browser on the NCSSM network

in either case USE THE LIGHT BEAM CLOCKS at the BOTTOM of the applet
 
1(8, 27)
.... and remember to solve for v/c, NOT v
lab
 
 


1st nuclear physics lab

lab E1
 
other
 

 
 


 
 
Monday,
March 9
Tuesday,
March 10
Wednesday,
March 11
Thursday,
March 12
Friday,
March 13
class
 look at the syllabus
and
course expectations

look at the textbook's Table of Contents
 
bring a copy of
"The Complete Guide to
Force Diagram Solutions"
to class (and have read it!)

make sure you have your calculator for class today
(I don't want to send you back,
and have to mark you late)


what we'll do
in class






we will talk more about violations of N's 1st law....

so in class yesterday, you all went from
(mostly) denying that you had ever seen an example of N's-1st-law violation to...
examples are everywhere.....

so let me tighten the requirements a little bit...
it's fairly easy to find examples in which YOU (as judged in your own frame) have 0 acceleration, yet have a net force acting on you.....

now how about some examples of the opposite situation:
objects which are accelerating, yet have zero apparent net force on them!


centrifugal forces and coriolis forces:

what are the equations describing the forces and how do they work?


the movie clip with the ball thrown on the merry-go-round...
make sure that the ball does indeed go straight (after release) in the earth frame by stepping through the clip frame by frame


begin classifying physics
quantities (simultaneity,
position, velocity, time intervals, etc.) as to whether they are relative or absolute to different observers

your book does one of these in the section 1(5) reading for today



learn the procedure for time dilation problems
(we do problem 10, chpater 1)
reading
(always done
before class)
 bring textbooks to class; we may read some


the TAN handout on
"Rotating Frames of Reference; Inertial Forces"

1(4 and 5 up through equation 1.9))


the BUFF handout on the absoluteness of perpendicular lengths

ALL of yesterday;s reading, if you did not do it
(we only read section 1(5) in class 

in-class
presentation





written
homework
(usually by 5 pm,
but sometimes for class)

use the applet
Rel_of_Simultaneity.htm at
T:\Student\kolena\Relativity_Physlets\
contents\s_relativity\sp_rel\section2_3.html

to  help answer the Tonya/Reid question

bring your answers to class

the improved version of yesterday's homework
 

sideways displacement of a baseball
thrown south from the pitcher's mound to  home plate, at a reasonable speed, in Durham

(or the displacement of any sports ball, kicked, thrown, or hit)

document the numbers you assume to start the problem

use the Coriolis effect formula that we learned in class!

lab
 
 
 
 
 
other