1' Activity 3, p265

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Plan for todays class
1. Activity 3, p2-65 2. Activity 4, p2-69 to
2-72 3. S/Q, p 2-71 to 2-72, will start at
110 4. Activity 5 5. Initial Ideas P2-75 to 2-7,
will start at 135 6. Break 7. Demonstrations
will start at 205 (bowling ball rolls down the
rail w/wo a block behind the rail 8. S/Q, p 2-84
to 2-86 will start at 300 9. Activity 6
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Childrens ideas about Force and motion P2-65
Common Idea 1 Impetus Theory Internal
Force Common Idea 2 Impetus Theory Force Runs
Out Common Idea 3 Forces have to do with living
things Common Idea 4 Constant motion requires
constant force Common Idea 5 The amount of
motion is proportional
to the amount of force Common Idea 6 If a
body is not moving there is
no force acting on it Common Idea 7 If a
body is moving there is force acting
on it in the direction of motion
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Plan for todays class
1. Activity 3, p2-65 2. Activity 4, p2-69 to
2-72 3. S/Q, p 2-71 to 2-72, will start at
110 4. Activity 5 5. Initial Ideas P2-75 to
2-77 6. S/Q, p 2-84 to 2-86 7. Activity 6 8.
Demonstrations 1F20-10
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S/Q, p2-71 to 2-72. S1 At about DVD time
000900 a student states that the ball
still had some more force to move a little bit
after the kick, and that this force came
from the foot. Another idea that was
expressed by the students is that the ball
stopped moving because the force ran out.
Why do you think these ideas make sense to the
students? You might consider what they
actually mean by the term force. (6)
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S2 In what ways were the ideas expressed by your
PET classmates (see Chapter 2 Activity 1
Initial Ideas) similar to the ideas
expressed by the children in the movie? In
what ways were they different? (7) S3 You are
much older than the children in the DVD
and have ha many more life experiences. Why
do you think your ideas would be so
similar in some cases? (1)
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Plan for todays class
1. Activity 3, p2-65 2. Activity 4, p2-69 to
2-72 3. S/Q, p 2-71 to 2-72, will start at
110 4. Activity 5 5. Initial Ideas P2-75 to 2-7,
will start at 135 6. Break 7. Demonstrations 8.
S/Q, p 2-84 to 2-86 9. Activity 6 10.
Demonstrations 1F20-10
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Initial idea, P 2-75 to P 2-77
(2)
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Use the pictures below to draw force diagrams for
the cart in the experiment described above the
first while it is speeding up during the initial
push, the second after the push, while the cart
is gradually slowing down. Explain briefly why
you drew the diagrams as you did.
(3)
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When you examined friction-type contact
interactions in Chapter 1, you gave a wooden
block a push across the table and saw it slow
and stop. We said this was due to friction but
how do you think friction actually works?
(4) Whether you think friction is a force or
not, explain what you think was actually
happening to slow the block down. (5)
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Plan for todays class
1. Activity 3, p2-65 2. Activity 4, p2-69 to
2-72 3. S/Q, p 2-71 to 2-72, will start at
110 4. Activity 5 5. Initial Ideas P2-75 to 2-7,
will start at 135 6. Break 7. Demonstrations
will start at 205 8. S/Q, p 2-84 to 2-86 9.
Activity 6 10. Demonstrations 1F20-10
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Plan for todays class
1. Activity 3, p2-65 2. Activity 4, p2-69 to
2-72 3. S/Q, p 2-71 to 2-72, will start at
110 4. Activity 5 5. Initial Ideas P2-75 to 2-7,
will start at 135 6. Break 7. Demonstrations
will start at 205 8. S/Q, p 2-84 to 2-86 will
start at 300 9. Activity 6 10. Activity 5 HW due
Monday, Feb. 23.
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S/Q, 2-84 to 2-86 S1 When you see a moving
object slow and stop, what do you think is
causing this to happen (if anything)?
(6) S2 What evidence from this activity
suggests that friction is a force that
opposes motion? (7)
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S3 How does the row of sticky notes serve as
an analogy to help understand how friction
works in slowing down a moving object?
That is, how does thinking about why the
sticky notes slow the block down help you
think about why the block slows down when
sliding across the sandpaper or the table?
(1) S4 Why do you think the block slows down
more rapidly on the sandpaper than on the
bare tabletop? Why does it slow down at all
on the apparently smooth tabletop? (2)
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S5 Why do you think the cart slows down very
gradually, even when no friction pad is
used, but slows quickly when the pad is
rubbing on the track? Use the pictures below
to draw force diagrams to illustrate the
difference between the two situations. Explain
your reasoning below the diagram. (4)
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S6 Suppose you could start an object moving and
then arrange for absolutely no forces to
act on it. How would it move from then on?
To help think about this question consider
the following
Suppose a spacecraft is at rest in deep space,
far from any starts or planets, so that no form
of friction or gravity is acting on it. The
main engine, at the rear of the spacecraft, is
fired for a period of 2 seconds (to start the
spacecraft moving) and is then shut off.
(5)
What do you think the motion of the spacecraft
would be like after the engine is shut off?
Explain your reasoning.
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Plan for todays class
1. Activity 3, p2-65 2. Activity 4, p2-69 to
2-72 3. S/Q, p 2-71 to 2-72, will start at
110 4. Activity 5 5. Initial Ideas P2-75 to 2-7,
will start at 135 6. Break 7. Demonstrations
will start at 205 8. S/Q, p 2-84 to 2-86 will
start at 300 9. Activity 6
Please throw away the bad markers, clean your
white board, turn off the monitor.
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Initial ideas, 2-99 to 2-101
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Sketch (and label) two lines on the blank
speed-time graph below for the two otherwise
identical carts being pushed by a weaker and
stronger force.
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Briefly explain the reasoning that led you to
draw the graphs as you did.
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Which cart do you think would be the first to
stop and start moving back toward you the one
with less mass, the one with more mass, or would
they act the same? Explain your reasoning.
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S/Q P 2-110 to 2-114 S1 When a single force acts
on an object, how does the rate at which
its speed changes depend on the strength o
that force? Is this true for both speeding
up and slowing down? What evidence supports
your answer?
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S2 Below is a speed-time graph for a cart that
was given a quick push along the track
and then gradually slowed down. Which
force do you think was stronger, the initial
push, or the one that slowed it down? How do
you know?
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S3 How does the mass of an object affect the
rate at which its speed changes, while a
force acts on it? What evidence supports
your answer? S4 Which would be easier to start
moving, a soccer ball or a bowling ball?
Which would be easier to stop if they were
moving at the same speed? Why do you think
this is?
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S5 At a practice session a soccer goalie is
practicing rolling a soccer ball along the
ground. The coach measures the speed of the
soccer ball and sees that, when the goalie
pushes as hard as he can, the ball has a speed of
15m/s just after it leaves the goalies
hands. A teammate plays a joke on the goalie
and substitutes a bowling ball (appropriately
painted) for the soccer ball. When the goalie
pushes as hard as he can on the bowling ball the
coach measures the balls speed to be only 2
m/s just after it leaves the goalies hands.
Assuming the goalie pushed with the same
strength force, for the same amount of time,
on both balls, write a scientific explanation
for why the bowling balls speed is much less
than the soccer balls speed, just after they
left the goalies hands.
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2-113
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How would the force strength the goalie has to
apply to the soccer ball to do this compare with
the force strength he has to apply to the
bowling ball? Explain how your answer fits with
the mathematical relationship you chose above.
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Plan for todays class
1. Important Corrections 2. Work from page 2-29
to 2-49 3. At 130, start the discussions
Initial ideas, page 2-29 to 2-31 4. Break 5. At
155, start the discussion S/Q, page 2-44 to
2-49 6. Demonstrations 7. Work on Activity 3 HW 1.
Please throw away the bad markers, clean your
white board, turn off the monitor.