1' Important Corrections

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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.
Discussion S/Q, page 2-44 to 2-49 6.
Demonstrations 1N10.10 and 1N 30.55 7. Work on
Activity 3 HW 1.
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S/Q, P2-22 S1 If a cart is at rest and a single
force acts on it, what happens?
The cart starts to move. If the same force
continues to act on the cart what happens
to the carts speed? (3) The speed increases
linearly with time.
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S2 In general, during the time a single force
with a constant strength acts on a moving
object, in the same direction as its
motion, what is the objects motion like?
Does it move at a constant speed, does
its speed continuously increase, or does
the speed only increase at first and then
become constant after a short time? What
evidence from this activity supports your
answer? (4)
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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.
Discussion S/Q, page 2-44 to 2-49 6.
Demonstrations 7. Work on Activity 3 HW 1 and 2.
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Initial idea, P 2-29 to P 2-31 What do you think
the motion of your friend would be like
(speeding up, slowing down, or constant speed)
during each of the four-second periods described
above? Would they all be the same or would they
all be different? Explain your reasoning. (Note
Assume the skateboard is well lubricated, so
that the effects of friction can be
ignored). (6)
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Sketch what you think the speed-time and
force-time graphs for your friend would look
like for the whole 12-second period described
above. (7)
Explain why you drew the graphs the way you did.
(7)
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Using the pictures of the skateboarder below,
draw a separate force diagram for each indicated
time. (Use your predicted speed-time and
force-time graphs above to guide you.) Be sure
to include both speed arrows of appropriate
lengths and any force arrows you think are
appropriate. (1)
2 seconds
6 seconds
10 seconds
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Plan for todays class
1. Important Correction 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.
Discussion S/Q, page 2-44 to 2-49 6.
Demonstration 7. Work on Activity 3 HW 1 and 2.
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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
and 2.
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S/Q, p2-44 to 2-49. Only the one having S and a
check mark. S1 If an object is already moving,
what effect on its speed does a single
force applied in the direction opposite
its motion have? If such a force continues to
act, what else may happen? (2)
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S2 Shown below are two force diagrams for a
moving cart upon which a force (from a
fan unit) is acting. What will the motion of
the cart be like in each case? (Speeding
up, slowing down, or constant speed.) Explain
your reasoning. (3)
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S3 In the last three activities you have studied
the effect of a single force acting on an
object under different circumstances.
When an object is moving, what would be evidence
that it is currently being acted upon by a
single force? (4)
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S4 In an experiment you performed in
Activity 2 of Chapter 1 you pushed a cart so that
it moved along the track. You then
gave it a quick tap with your hand to
change its direction and send it back toward
the starting point. (5)
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Describe the situation using a diagram The force
diagram currently shows a cart moving to the
left. Draw and label the appropriate force arrow
for the Interaction with the hand that will make
the cart Reverse direction. (6)
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(1)
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If you think a statement is true for one of
the four moments listed above, place a check
mark in the appropriate box in the table. If you
think it is false for that moment, leave the box
blank.
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(2)
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(3)
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Now answer these questions about the relationship
between the direction in which a single force
acts on an object and the transfer of mechanical
energy in the corresponding contact interaction.
When a single force acts on an object in the same
direction as its motion, is mechanical
energy transferred into or out of the
object? How do you know? (4)
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When a single force acts on an object in the
direction opposite to its motion, is mechanical
energy transferred into or out of the
object? How do you know? (5)
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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.
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Explanation (P2-27) Why did the cart with a
fan-unit attached continue to speed up as it
moved along the track?
A. Describe the situation using a diagram
B. Write the narrative
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Initial idea, P 2-35 to 2-37 Imagine you started
a low-friction cart moving along the track (or
table) in front of you and then, while it was
still moving, you gave it a very gentle tap with
your hand in the opposite direction to its
motion. After your tap note that the cart is
still moving in its original direction.
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Sketch a speed-time graph for the motion of the
cart. Be sure to include the motion of the cart
before you tap it, while you are touching it,
and after your hand has lost contact.
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Briefly explain your force diagrams and how the
speed arrows and force arrows (if any) you drew
on all three diagrams correspond to your
predicted speed-time and force-time graphs.
31
Briefly explain your reasoning behind your
graph. Use the pictures below to draw three
force diagrams (including both force and speed
arrows where appropriate) for the cart one for
a moment before the tap (for which the speed
arrow is already included), one during the short
time that you were tapping it, and a third for a
moment just after your tap. Remember to label
any force arrows you draw.
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Briefly explain the reasoning behind your force
arrows and speed arrows.