Clicker Questions for NEXUS/Physics
Models of Forces
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.
Two springs, are linked together and pulled
from opposite ends by equal tension forces T.
The spring constants are NOT the same: k1 >> k2.
The system is at rest. How do the forces that the
springs exert on each other compare?
A.
B.
C.
D.
E.
They are equal but not equal to T.
They are equal and equal to T.
Spring 1 exerts a larger force on spring 2, than 2 does on 1.
Spring 2 exerts a larger force on spring 1, than 1 does on 2.
Something else.
1
2
Two springs, are linked together and pulled
from opposite ends by equal tension forces T.
The spring constants are NOT the same: k1 >> k2.
The system is at rest. How do the the amounts
that the springs stretch compare and how do
you know ?
A. They are equal because they exert equal forces on each other.
B. They are equal because the larger k of spring 1 is compensated
for by its larger mass.
C. Spring 1 stretches more because it has a larger k than spring 2.
D. Spring 2 stretches more because
it has a smaller k than spring 1.
2
1
E. Spring 2 stretches more
because it feels a larger
force from spring 1 than
spring 1 feels from spring 2.
In the figure is shown the force needed
to stretch an uncoiled DNA molecule.
Suppose we measure the spring constant of
DNA at three points: When it was 5%, 75%,
and 125% longer than its unstretched length;
Which measurement would yield the largest
spring constant?
A.
B.
C.
D.
5%
75%
125%
They would all be
the same
Consider two blocks made of the same
material with the same cross sectional area
but one twice as long as the other. If the
same compressional forces are exerted on
both blocks
A. They will compress by the same
amount.
B. The short block will compress by twice
as much.
C. The long block will compress by twice
as much.
D. There is not sufficient information
given to tell.
Consider two blocks made of the same
material with the same length but one twice
cross sectional area as the other. If the same
compressional forces are exerted on both
blocks
A. They will compress by the same
amount.
B. The wide block will compress by twice
as much.
C. The narrow block will compress by
twice as much.
D. There is not sufficient information
given to tell.
Suppose I start pushing a box along a table that
has a box sitting on top of it. The boxes slowly start
moving and the top one doesn’t slip.
If there is a friction force from box A on box B,
in what direction does it point?
A.
B.
C.
D.
E.
F.
There is no friction between the boxes.
Left
Right
Up
Down
You can’t tell
from the information
given.
Suppose I start pushing a box along a table that
has a box sitting on top of it. The boxes slowly
start moving and the top one doesn’t slip.
Box B is accelerating to the right. What
unbalanced force is responsible for this?
A.
B.
C.
D.
E.
The push of the finger.
The normal force of box A on B.
The friction force of box A on B.
The weight of box B.
Something else.
If I drop a light object (a wooden ball)
and a heavy object (a steel ball) from
4 m, which will hit the ground first?
1.
2.
3.
4.
The light one (by a lot)
The heavy one (by a lot)
About the same
You can’t tell from
the information given.
If I drop a light object (a paper ball)
and a heavy object (a steel ball) from
4 m, which will hit the ground first?
1.
2.
3.
4.
The light one (by a lot)
The heavy one (by a lot)
About the same
You can’t tell from
the information given.
Which ball will hit first?
A. The shot one
B. The dropped one
C. They’ll hit
at the same time
D. You can’t tell
from the
information given.
Two dense objects (so air drag can be ignored)
are shot straight up at the same time from the
same height.
Object A is shot with a speed of 1 m/s, object B
with a speed of 2 m/s. Which takes longer
to come back to its starting point?
A.
B.
C.
D.
E.
Object A
Object B
Both take the same.
I can’t tell since you didn’t give me the masses.
I can’t tell for some other reason.
Two dense objects (so air drag can be
ignored) are shot up at the different angles
at same time from the same height.
They follow the trajectories shown.
Which will hit its target first??
A.
B.
C.
D.
E.
Object A
Object B
Both the same.
I can’t tell since you didn’t give the masses
I can’t tell for some other reason.
A
B
The cart runs along a horizontal track.
Part way along it strikes a small hook that
causes the cart to throw the ball straight upward.
Will the cart catch the ball?
A.
B.
C.
D.
E.
No. The ball will fall
behind the cart.
No. The ball will fall
ahead of the cart.
Yes
It depends on how fast
the cart is traveling.
You can’t predict.
Now the cart is attached to a string that runs
over a pulley to a weight. This exerts a
constant horizontal tension force on the cart.
Will the cart catch the ball?
A.
B.
C.
D.
E.
No. The ball will fall
behind the cart.
No. The ball will fall
ahead of the cart.
Yes
It depends on how fast
the cart is traveling.
You can’t predict.
Now the string is removed but the track
is tilted down. Will the cart catch the ball?
A.
B.
C.
D.
E.
No. The ball will fall
behind the cart.
No. The ball will fall
ahead of the cart.
Yes
It depends on how fast
the cart is traveling.
You can’t predict.
In the situations below, a mover pushes two crates
on a horizontal surface, and they move together
with a constant a. In which situations are the forces that
the two crates exert on each other equal in magnitude?
a. Situation I only. e. In two or more of the situations.
b. Situation II only. f. In all of the situations.
c. Situation III only. g. You can’t tell from what’s given.
d. Situation IV only.
The mover is pushing two crates along a frictionless
horizontal surface and the crates are slowly increasing
their speed. Consider the following four forces:
•F1 -- the force that the mover exerts on crate A
•F2 -- the force that crate B exerts on crate A
•F3 -- the force that crate A exerts on crate B
•F4 -- the force that crate A exerts on the mover
Which of the following correctly compares the
magnitudes of these forces?
a. F1 = F2 = F3 = F4
b. F1 = F2 = F3 > F4
c. F1 = F4 > F2 = F3
d. F1 > F3 > F2 > F4
e. None of the above.
A paramecium swimming through a fluid is
moving at approximately a constant velocity
as a result of wiggling its cilia. What can you
say about the net force that is being exerted
on it while it is doing this?
A.
B.
C.
D.
It is significantly greater than zero
It is a little bit greater than zero
It is equal to zero
It cannot be determined from
the information given.
A paramecium swimming through a fluid is
moving at approximately a constant velocity as
a result of wiggling its cilia. What can you say
about the magnitude of the normal force that the
paramecium’s cilia exert on the water (Ncw)
compared to the magnitude of the normal force
that the water exerts back on the cilia (Nwc) ?
A.
B.
C.
D.
E.
F.
Ncw is significantly greater than Nwc
Ncw is a little bit greater than Nwc
Ncw = Nwc
Ncw is significantly less than Nwc
Ncw is a little bit less than Nwc
It cannot be determined from
the information given.
A paramecium swimming through a fluid is
moving at approximately a constant velocity as
a result of wiggling its cilia. What can you say
about the magnitude of the normal force that the
paramecium’s cilia exert on the water (Ncw)
compared to the magnitude of the viscous force
that the water exerts on the paramecium (Fwp) ?
A.
B.
C.
D.
E.
F.
Ncw is significantly greater than Fwp
Ncw is a little bit greater than Fwp
Ncw = Fwp
Ncw is significantly less than Fwp
Ncw is a little bit less than Fwp
It cannot be determined from
the information given.