PHYS 342
F ll 2010
Fall 2010
Lecture 33: Time Dilation
and Length Contraction
Ron Reifenberger
Birck Nanotechnology Center
Purdue University
Time dilation and length contraction are two of
the most surprising
implications of the Lorentz-
Einstein transformations of special relativity
Einstein transformations of special relativity.
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Lecture 33

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What is Space?
Space is what we measure with a measuring rod
What is Time?
Ti
i h
i h
l
k
Time is what we measure with a clock
NOTE
In some of the examples that follow,
we will
require the
difference
in coordinates for a
pair of events In other examples the
2
pair of events. In other examples, the
coordinate of some object (like a clock) will
remain the same.
(see last lecture.)

How do we tell time?
Light Clocks (no mechanical parts)
http://webphysics.davidson.edu/course_material/py230l/relativity/relativity-ex1.htm
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Clock
at rest
in S’ frame
Time Dilation
y’
S
S’
in S frame
'
'
'
f
x
x
v t
y
y
y
y
v
f
t
1
’
t
2
’
'
'
'
f
z
z
v x
t
t
x
x’
x’
1
2
2
'
f
c
u
v
u
1
'
f
v
c
u
1
1
1
2
'
'
f
v x
t
t
c
Trust the equations:
Takes you
f
S ’ t
S
1
2
2
2
'
'
f
v x
t
t
c
from S ’ to S
2
1
2
1
'
'
'
t
t
t
t
t
t
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