Document

Report
Clicker Questions for NEXUS/Physics
Kinematics
A note on usage:
The clicker slides in this booklet are meant
to be used as stimuli to encourage class discussion.
They are intended for use in a class that attempts
to help students develop a coherent and sophisticated
understanding of scientific thinking.
They are NOT intended as items to test whether
students are “right or wrong” or “know” the correct
answer by one-step recall if enough cues are given.
This has a number of instructional implications
that are reviewed in general on the next four slides.
The individual slides also contain annotations
discussing their intended use.
Usage: 1
• Feedback
One of the most important values of a clickerresponse system is to provide instructors with
some understanding of what students are thinking.
Good clicker questions can be highly revealing
(and surprising). But the critical fact is not that the
students make mistakes but to use those mistakes
to probe their thinking and find out why.
This raises the importance of a rich subsequent
discussion well above “letting the students know
what the right answer is.”
Usage 2:
• Student-student interactions
The critical value for student learning occurs
in what happens after a clicker question has
obtained a mixed response from the students.
The standard next cue is, “Find someone
who disagreed with the answer you chose
and see if you can convince them.”
After a minute or two of discussion, a second click
may show students having moved dramatically
towards the correct answer. A brief call for who
changed their answer and why can lead to a
useful exchange. When they have not moved
significantly, more discussion is called for.
Usage: 3
• Incompletely specified questions
Some items have questions that are simple if idealized
assumptions are made, subtler if they are not. Part of
the discussion of these items are intended to include
issues of modeling, idealizations, and hidden
assumptions.
• Questions where answers are not provided.
In these items, the intent is to have students come up
with potential answers and have the instructor collect
them and write them on the board.
Occasionally, especially at the beginning of a class, it may
take some time before students are willing to contribute
answers. It can help if you have some prepared answers
ready, walk around the class, and put up the answers as if
they came from the students. This can help students get
more comfortable with contributing.
Usage: 4
• Cluster questions
Some questions are meant to be used as part of a
group of questions. In this case, resolving the answers
to individual questions is better left until the entire
group is completed. The value of the questions are
often in the comparison of the different items and in
having students think about what changes lead to what
differences and why.
• Problem solving items
In these items (indicated by a pencil cluster logo), the
intent is to have students work together to solve some
small problem. After a few minutes, ask the groups to
share their answers, vote on the different answers
obtained, and have a discussion.
dx
v=
dt
The 1D velocity is defined as
What is true about this velocity?
1.
2.
3.
4.
It is always positive.
It is only negative if x is negative.
It can be positive or negative but only for positive x.
It can be positive or negative for both positive and
negative x.
Example
• If I place the sonic ranger at the left
side of the room and you walk slowly
towards it at almost a constant velocity
what will the position graph look like?
• Generate the graph on your
whiteboard.
x
x
(2)
(1)
t
t
x
x
(3)
(4)
t
t
x
x
(6)
(5)
t
t
Example
• If I place the sonic ranger at the left
side of the room and you walk slowly
towards it, at almost a constant
velocity what will the velocity graph
look like?
• Discuss with your group and sketch
the consensus graph on your
whiteboard.
v
v
(2)
(1)
t
t
v
v
(3)
(4)
t
t
v
v
(6)
(5)
t
t
A person initially at point P in the illustration stays there
a moment and then moves along the axis to Q and stays
there a moment. She then runs quickly to R, stays there
a moment, and then strolls slowly back to P. Which of the
position vs. time graphs below could correctly represent
this motion if the scales were correct?
Graphing Velocity:
Figuring it out from the motion
• An object in uniform motion
has constant velocity.
• This means the instantaneous velocity
does not change with time.
Its graph is a horizontal line.
• You can make sense of this by
putting your mind in “velocity mode”
and running a mental movie.
Example
• How do you have to walk to make the sonic
ranger produce the following velocity graph?
• Draw the position graph.
Example
x
x
• A ball rolling on a level track travels
at almost a constant velocity.
Assuming it takes a negligible time to get
up to speed, what does the graph of its
position look like as a function of time?
Please make your selection...
x
x
x
(1)
(3)
(2)
t
x
(5)
x
t
t
x
(6)
(4)
t
(7) other
t
t
Example
v
v
• A ball rolling on a level track travels
at almost a constant velocity.
Assuming it takes a negligible time to get
up to speed, what does the graph of its
velocity look like as a function of time?
Please make your selection...
v
v
v
(1)
(3)
(2)
t
v
v
v
(5)
(4)
t
(7) other
t
t
(6)
t
t
Example
x
x
n A ball rolls is rolling at a constant speed
along a horizontal track as shown.
It comes to a hill and has enough speed
to get over it. By thinking about its speed
as it goes, sketch a graph of the position
of the ball as a function of time.
Please make your selection...
x
x
(1)
x
(2)
(3)
t
t
x
t
x
(4)
x
(5)
t
(7) other
(6)
t
t
Example
v
v
n A ball rolls is rolling at a constant speed
along a horizontal track as shown.
It comes to a hill and has enough speed
to get over it. By thinking about its speed
as it goes, sketch a graph of the velocity
of the ball as a function of time.
For each of the next three clicker
problems, write on your white
board
• The variable
• The number of the graph you
chose
• A sketch of the graph you chose
(with the axes labeled)
A small toy car can move along a horizontal
track. Its position is measured by a sonic
ranger. When the motion detector is turned on
the car is moving towards the left and is
slowing down at a uniform rate.
Which would be the
graph of velocity shown
on the screen?
A small toy car can move along a horizontal
track. Its position is measured by a sonic
ranger. When the motion detector is turned on
the car is moving towards the left and is
slowing down at a uniform rate.
Which would be the
graph of position
shown on the screen?
A small toy car can move along a horizontal
track. Its position is measured by a sonic
ranger. When the motion detector is turned on
the car is moving towards the left and is
slowing down at a uniform rate.
Which would be the
graph of acceleration
shown on the screen?
Are your three graphs consistent?
Discuss your choices
with your working group.
What did you decide?
1. The were all consistent.
2. Two were consistent but a one was not.
3. They were not at all consistent.
Figuring out acceleration
• Look at the y-t, and vy-t plots for a ball thrown
by a juggler and going up and down.
• Acceleration is
the derivative
of the velocity.
How is the
velocity
changing?
Why?
dv
a=
dt
When the ball is at the highest point
what is its velocity?
A.
B.
C.
D.
Positive (upward)
Negative (downward)
Zero
Cannot be
determined
When the ball is at the highest point
what is its acceleration?
A.
B.
C.
D.
Positive (upward)
Negative (downward)
Zero
Cannot be
determined
This graph shows the altitude of one of
balls in the juggler video after he has
relased it and before he touches it again.
Where is the ball at its highest point?
• A.
• B.
• C.
• You can’t tell.
B
A
C
This graph shows the velocity of one of
balls in the juggler video after he has
relased it and before he touches it again.
Where is the ball at its highest point?
• A.
• B.
• C.
• A and C
• You can’t tell.
A
B
C
Which of these graphs
looks like
the acceleration
graph for the situation
shown on the previous
two slides?
•A
•B
•C
•D
• None of these
What does the previous result tell
us about the net force the ball feels
when nothing is touching it?
Discuss
In the figure below is shown a graph of
the position of a vesicle that was observed
to move along a straight line.*
At what instant of time is the vesicle moving
with the highest speed?
• Force-Velocity Curves of Motor Proteins Cooperating In Vivo,
• Y. Shtridelman, et al., Cell Biochem Biophys. 52(1): 19–29 (2008).
In the figure below is shown a graph of
the position of a vesicle that was observed
to move along a straight line.*
At what instant of time is the vesicle moving
with the slowest speed?
• Force-Velocity Curves of Motor Proteins Cooperating In Vivo,
• Y. Shtridelman, et al., Cell Biochem Biophys. 52(1): 19–29 (2008).
In the figure below is shown a graph of
the position of a vesicle that was observed
to move along a straight line.*
At what instant of time is the vesicle magnitude
of the vesicle’s acceleration the largest?
• Force-Velocity Curves of Motor Proteins Cooperating In Vivo,
• Y. Shtridelman, et al., Cell Biochem Biophys. 52(1): 19–29 (2008).
In the figure below is shown a graph of
the position of a vesicle that was observed
to move along a straight line.*
At what instant of time is the vesicle feeling a
net force of the greatest magnitude?
• Force-Velocity Curves of Motor Proteins Cooperating In Vivo,
• Y. Shtridelman, et al., Cell Biochem Biophys. 52(1): 19–29 (2008).

similar documents