With and Without a Net
Name: ___________________________
INTRODUCTION:
Answer these questions based on the introductory reading:
1. When is there a net force on an object?
2. What can you say about the net force when you are moving at constant velocity?
3. What is it you can feel?
4. What is it that causes a change in momentum?
MATERIALS :
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
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1 coffee filter
1 stop watch
Some paper clips
PROCESS & PROCEDURE:
CAUTIONS!!!!!
Make sure the table or chair you stand on is STABLE!
If you have balance problems, DO NOT STAND ON THE TABLE OR STOOL!
1. Pay close attention as your teacher demonstrates a model of a parachute.
2. At your lab station, extend the demonstration by performing steps 2a and 2b. Record your results on
the next page using sketches and captions.
a. Standing on a stool, hold a coffee filter above your head, and release it. Focus your attention on
whether the filter speeds up, slows down, or neither as it falls. Record the time it takes to reach
the floor.
b. Repeat step 2a with 2, 4, and then 6 paper clips in the filter.
Questions to consider: When did velocity increase? When did velocity remain constant?
Group Observations
Class Observations
Fall Time
Velocity Observations
Fall Time
Velocity Observations
0 Paperclips
2 Paperclips
4 Paperclips
6 Paperclips
Read Going Terminal to prepare for sketching scaled vector diagrams of the forces acing on the coffee filter at
several points during its fall.
Below, draw scaled vector sketches showing all the vertical forces acting on the coffee filter in the
following situations. Include highlight comments and a summary caption.
Force diagrams of the coffee filter empty
Force diagrams of the coffee filter holding 6
paperclips
Filter in your Hand
Vector Sketch What I see:
Filter in your Hand
Vector Sketch
What It Means:
Filter Shortly after Release
Vector Sketch What I see:
What It Means:
Filter Shortly after Release
Vector Sketch
What It Means:
Filter Just Before Landing
Vector Sketch What I see:
What I see:
What It Means:
Filter Just Before Landing
Vector Sketch
What It Means:
Summary:
What I see:
What I see:
What It Means:
Summary:
WATCH THE VIDEO FORCES & MOTION
3. Compare the motion of the coffee filter to a chair as you complete Steps 3a-c:
a. How is the motion of the coffee filter similar to that of the chair?
b. When does the Fnet = 0 for the coffee filter? What about the chair?
c. Draw scaled and labeled vector sketches showing all the horizontal forces acting on the chair at
the 3 different times shown on page 11. Include highlight comments and a summary caption.
Diagrams of the horizontal forces on the chair
Chair at Rest: v=0
Chair while Velocity is Increasing
Chair moving at Constant
Velocity
Vector Sketch
Vector Sketch
Vector Sketch
What I see…
What I see…
What I see…
What it means…
What it means…
What it means…
Summary caption:
4. Compare the motion of a chair across the floor to accelerating a car by completing Steps 8a-c:
a. How is the motion of the chair across the floor similar to increasing your speed in a car at a green
light?
b. Draw scaled and labeled vector sketches showing all the horizontal forces acting on the car, from
a stop to a constant velocity. Include highlight comments and a summary caption.
Diagrams of the horizontal forces on the car at 3 positions
Car at Rest
Car increasing Velocity while
Hitting the Gas
Car traveling at Constant
Velocity
Vector Sketch
Vector Sketch
Vector Sketch
What I see…
What I see…
What I see…
What it means…
What it means…
What it means…
Summary caption:
STOP & THINK: PART I
1. Describe the motion of an object if the net force is zero. Give examples (in words &/or drawings).
2. Newton’s First Law (also known as the “Law of Inertia”) states: “Objects in motion stay in motion and
objects at rest stay at rest, unless acted upon by an outside net force.” Explain whether this activity supports
or refutes (goes against) this statement by providing direct evidence from the activity.
3. Imagine a “clever” teenager who wanted to avoid a football workout. The conversation with a coach might go
like this:
Teenager: “It’s totally useless for me to try to push the blocking sled.”
Coach: “You think so!? Why is that?”
Teenager: “Because of a law of nature.”
Coach: “This I’ve got to hear.”
Teenager: “I have been learning that forces come in pairs, equal in size and opposite in direction. When I push
on the sled, the sled pushes back on me with an equal, but opposite, force. The forces cancel. Therefore, I can
never get the sled moving. It’s useless!”
Coach: “Now I’ve heard it all! I need to talk to that science teacher…”
Analyze the motion of the blocking sled:
a. Use vector arrows to label the pairs of forces that occur at each of the starred areas of the sketch.
b. Complete the table below by commenting on all the horizontal pairs of forces important to the question of
whether the teenager can push the sled.
Objects involved
in force pair
Teenager and
sled
Teenager and
ground
Sled and ground
Relative size of forces in pair
The force of the teenager on the
sled is equal and opposite the
force the sled on the teenager.
Relative size of force pair compared
to other two force pairs
c. Decide who is correct in his reasoning. Is it the football player trying to get out of pushing the
blocking sled, or the coach who wants the player to complete the workout? Write a statement giving
evidence to support your decision. To develop your statement, consider the forces that would cause a change in
velocity of the sled.
4. How can you tell when there is or is not a net force acting on an object? Use your experiences from this
activity to answer this question.
VIDEO NOTES: RELAXING WITH IMPULSE