FRAME
O
S
F
Reference
Pass out the Frames
of Reference notes
11/5/09
Have you ever, in a car wash…
jammed your foot on the brake
when you felt the car moving
and then felt foolish when it
wasn’t.
11/5/09
Have you ever …
thrown a ball up while riding
in a car or bus and wondered
how it looked from outside
the car or bus?
11/5/09
Have you ever, while stopped
at a stoplight …
jammed your foot on the
brake when you felt the car
moving and then felt foolish
when it wasn’t.
11/5/09
Play the video…
“FRAMES OF REFERENCE”
Only play from 0:00 to 3:15
Works best in Quicktime
11/5/09
Newton’s Law of motion holds
equally well whether a reference
frame is not moving at all….
or moving with constant
velocity
These reference frames are
called inertial reference frames.
11/5/09
When are you in an inertial
frame of reference?
If you are not moving or
moving with a constant
velocity.
11/5/09
Play the video…
“FRAMES OF REFERENCE”
Now play from 3:15 to 9:58
Works best in Quicktime
11/5/09
Let’s introduce a new way of naming velocities
Label for reference
frame (g = ground)
Vmg
Label for object (m = man)
11/5/09
Let’s learn how to add relative velocities
To solve for a specific
velocity, you must use
other relative
velocities to find your
answer.
Set up an equation so
that the outer
subscripts are the
same as your final
answer.
Vpm +Vmg = Vpg
Vpm +Vmg = Vpg
notice these are both m’s
Then just do the
math. Sometimes this
is simply addition,
later we see this may
involve a triangle.)
11/5/09
Let’s learn how to add relative velocities
Vpm +Vmg = Vpg
To solve for a specific
velocity, you must use
other relative
velocities to find your
answer.
Set up an equation so
that the outer
subscripts are the
same as your final
answer.
Then just do the
(5 m/s) + (2 m/s) = Vpg math. Sometimes this
is simply addition,
7 m/s = Vpg
later we see this may
You may have noticed the puck moved quite rapidly involve a triangle.)
11/5/09
Play the video…
“FRAMES OF REFERENCE”
Now play from 9:58 to 13:25
Works best in Quicktime
11/5/09
Play the video…
“FRAMES OF REFERENCE”
Now play from 9:58 to 13:25
Works best in Quicktime
11/5/09
End of Thursday’s notes….
11/6/09
Begin Day Two Notes
11/5/09
Play the DVD…
“Physics Phun”
Click on Kinematics
Play Intro to Reference Frames
11/5/09
Play the DVD…
“Physics Phun”
Click on Kinematics
Play Relative Motion on a Train
11/5/09
Have you ever...
seen books sliding across
the car seat as you hit your
brakes?
11/6/09
Play the video…
“FRAMES OF REFERENCE”
Now play from 13:25 to 17:04
Works best in Quicktime
11/5/09
Newton’s laws work in an
inertial frame of reference.
They do not work in a noninertial (accelerated) frame of
reference.
11/6/09
Have you ever...
seen books sliding across
the car seat or the dash as
you turned a corner?
11/6/09
Play the video…
“FRAMES OF REFERENCE”
Now play from 17:04 to END
Works best in Quicktime
11/5/09
Thinking back to this
question,
Have you ever seen books
sliding across the car seat or
the dash as you turned a
corner?
11/6/09
In the car’s reference frame,
what is the force(s) acting on the
books?
There are none.
Why not?
We are using Newton’s laws in a
non-inertial (accelerated) frame.
11/6/09
If the reference frame is
accelerating…
Newton’s laws of motion do
not work.
11/6/09
Is the earth accelerating?
If so then why do Newton’s
laws work?
The expected differences are
too small to observe.
11/6/09
Summary:
Newton’s laws apply in inertial
reference frames, but they do
not apply in accelerated
reference frames.
11/6/09
Let’s learn how to add relative velocities in two dimensions
Just like before we
must use other
relative velocities to
find your answer.
Vcs +Vsg = Vcg
A canoe attempts to cross a
stream, and the stream
flows “upstream”.
Set up an equation so
that the outer
subscripts are the
same as your final
answer.
Now we must use a
triangle to find a
resultant.
11/5/09
Let’s learn how to add relative velocities in two dimensions
Just like before we
must use other
relative velocities to
find your answer.
Vcs +Vsg = Vcg
If it’s a right triangle, Use
the Pythagorean Theorem
to find the resultant value.
Use trig functions (sin, cos,
tan) to find the angle.
Set up an equation so
that the outer
subscripts are the
same as your final
answer.
Now we must use a
triangle to find a
resultant.
11/5/09
If there is time to review…
Open this website
http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=140.0
Hover the mouse over an object to change the
frame of reference
Click on info to see the relative velocities
Again, change the frame of reference to see how the
values (and sometimes direction) change
11/5/09
If there is time to review…
Open this website
http://www.mrwaynesclass.com/teacher/ReferenceFra
mes/FrameOfRef.swf
Play this short animation
Determine which solution is best
In fact, both are possible explanations for the motion of
the stars and spaceship
11/5/09