1/17/10
Reading
Assignment
  Chapter
37,
sections
1‐6
(covered
Monday
and
today)
  Chapter
37,
sections
7‐8
(will
be
covered
PH
120
Friday)
  Virtual
office
hours
–
Thursday
10‐?
p.m.
β
=
V
/
C
Δτ
=
Δt’
if
S’
is
the
rest
frame
of
the
clock
The
“stretching
out”
of
the
time
interval
is
called
time
dilation.
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1/17/10
QUESTIONS:
2
1/17/10
Molly
flies
her
rocket
past
Nick
at
constant
velocity
v.
Molly
and
Nick
both
measure
the
time
it
takes
the
rocket,
from
nose
to
tail,
to
pass
Nick.
Which
of
the
following
is
true?
A.  Nick
measures
a
shorter
time
interval
than
Molly.
B.  Molly
measures
a
shorter
time
interval
than
Nick.
C.  Both
Molly
and
Nick
measure
the
same
amount
of
time.
3
1/17/10
An
example
Molly
flies
her
rocket
past
Nick
at
constant
velocity
v.
Molly
and
Nick
both
measure
the
time
it
takes
the
rocket,
from
nose
to
tail,
to
pass
Nick.
Which
of
the
following
is
true?
A.  Nick
measures
a
shorter
time
interval
than
Molly.
B.  Molly
measures
a
shorter
time
interval
than
Nick.
C.  Both
Molly
and
Nick
measure
the
same
amount
of
time.
  Suppose
Bob
is
a
NASA
astronaut
who
travels
at
0.8c
to
a
star
4
light
years
away.
(1
light
year
=
distance
light
travels
in
1
year)
  Steve
works
for
NASA
on
Earth
  Steve
measures
the
time
as
An
example
An
example
  When
Bob
returns,
Steve
is
10
years
older.
  Using
time
dilation,
Steve
calculates
that
Bob
  Steve
calculates
will
have
aged
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1/17/10
An
example
An
example,
continued
  Bob
has
also
studied
relativity.
He
sees
Earth
  On
the
first
part
of
the
trip,
Bob
sees
the
star
(and
Steve)
moving
at
‐0.8c
relative
to
him.
  So
he
decides
Steve’s
clocks
should
run
slow
move
at
‐0.8c
for
3
years
  Who
is
right?!
The
distance
L
between
two
objects,
or
two
points
on
one
object,
measured
in
the
reference
frame
S
in
which
the
objects
are
at
rest
is
called
the
proper
length
ℓ.
The
distance
L'
in
a
reference
frame
S'
is
The
distance
L
between
two
objects,
or
two
points
on
one
object,
measured
in
the
reference
frame
S
in
which
the
objects
are
at
rest
is
called
the
proper
length
ℓ.
The
distance
L'
in
a
reference
frame
S'
is
NOTE:
Length
contraction
does
not
tell
us
how
an
object
would
look.
The
visual
appearance
of
an
object
is
determined
by
light
waves
that
arrive
simultaneously
at
the
eye.
Length
and
length
contraction
are
concerned
only
with
the
actual
length
of
the
object
at
one
instant
of
time.
NOTE:
Length
contraction
does
not
tell
us
how
an
object
would
look.
The
visual
appearance
of
an
object
is
determined
by
light
waves
that
arrive
simultaneously
at
the
eye.
Length
and
length
contraction
are
concerned
only
with
the
actual
length
of
the
object
at
one
instant
of
time.
5
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QUESTION:
6
1/17/10
Consider
two
reference
frames
S
and
S'.
An
event
occurs
at
coordinates
x,
y,
z,
t
as
measured
in
S,
and
the
same
event
occurs
at
x',
y',
z',
t'
as
measured
in
S'
.
Reference
frame
S'
moves
with
velocity
v
relative
to
S,
along
the
x‐axis.
The
Lorentz
transformations
for
the
coordinates
of
one
event
are:
7