Download PF Intro to Forces 02-08 - A TIME for Physics First

9th grade in the Physics First Curriculum
What is the Physics First program?
INTRODUCING FORCES
 Physics First is a national movement to teach a
year-long Physics course in 9th grade
 In Missouri, MO-DESE has funded a partnership
led by Columbia Public Schools and Univ. of
Missouri-Columbia to develop curriculum and
conduct professional development (PD)
 The first summer of PD was conducted in 2006
for 60 teachers, who will return in 2007 and 2008
 A smaller protégé class of 22 was accepted for
2007 and 2008.
Jaime Horton
Amy Scroggins
Carthage R-9 School District
Meera Chandrasekhar
Dorina Kosztin
Department of Physics and Astronomy
University of Missouri, Columbia
Support: Missouri Department of Elementary and
Secondary Education
Math-Science Partnership Grant
www.physicsfirstmo.org
Curriculum
 Year 1: Uniform and Accelerated Motion, Forces,
and Newton’s Laws
 Year 2: Motion in 2D, Energy, Momentum, and
Electricity
 Year 3: Electromagnetism, Waves, and Heat
 Pedagogy - based on Modeling, Inquiry & 5E
 Year-long follow-up and support
Students’
Students’ Beliefs about Forces
 Only animate objects can exert forces
 Forces are seen as merely influences on an
object’s motion, not as forces
 Impetus theory – e.g., force of throw travels with
ball
 Forces are viewed from the perspective of the
applier, rather than that of the object
 Tension/Normal forces not well understood
 Today - parts of the Unit 3: Introducing Forces
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Learning Objectives
 A force is an interaction between two objects (an agent
and a receiver)
 Identify forces acting on an object in terms of a receiver,
one or more agents, effects and direction
 Draw a force diagram for the object/receiver
 Describe the parameters that can change/affect amount
of the force
 State whether resultant force causes the velocity of the
object to be constant or changing
 Determine if forces acting on an object are
balanced/unbalanced
Big Understandings and Skills
 Big Understandings:
 A force is a push or a pull on an object.
 A force is a vector - has both amount (magnitude) and direction.
 A force requires an agent (something does the pushing or
pulling).
 A force is either a contact force or a long-range force (gravity is
the only long-range force in this unit).
 The force acting on an object may be the sum of several forces
(net force).
 Skills:
 Identifying forces
 Figuring out net force
(GLEs: 2.2.A.a, 2.2.B.c, 2.2.D.c, 2.2.D.d, 2.2.D.e)
In this unit…
unit….
 Part 1:
 ID different forces, their agents, receivers, effects
 Investigate in more detail: normal forces, gravity,
friction and elastic forces
 Part 2:
Activity: Exerting Forces
 Forces as vectors
 Work with several forces acting on an object
 draw force diagrams
 understand graphically how forces balance
 if forces do not balance, obtain the net force
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Pre-lab questions
 How do you know when you exert a force?
 Could you make a list of the different forces you
exerted in the last five minutes?
 How strong a force do you think you can exert?
 What do you think is meant by the term “force”?
 What are some things that can happen to an
object when a force acts on it?
Exerting Forces - Directions
At each station, create a chart with the following:
 A picture or diagram showing each situation
 Are there any forces exerted?
 What/who is applying the force?
 What object receives the force?
 What effect does the force have on the object?
 What do you think is the name of the force
demonstrated at this station?
Two General Categories of Forces
Whiteboard feedback from Exerting Forces activity
 Contact forces – those that require the agent
that causes the force to be in contact with the
object.
Examples: pushing, pulling, squeezing,
stretching, …..
 Field Forces – those that act at a distance.
Examples: gravity, magnetism, electricity
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Examples: Contact and Field forces
Gravity:
brings the skier down
Tension:
Holds the pot
Normal:
holds the owl up
Friction:
slows you down
The Four Forces of Nature-2
 Gravity – due to the mass of objects. Holds
stars, planets together.
 Electromagnetic – due to the charge on objects.
Responsible for binding of atoms and molecules.
 Strong – holds neutrons and protons together,
restricted to the nuclei of atoms
 Weak – short-range force, produces instability in
certain nuclei
The Four Forces of Nature
 Many forces on the macroscopic level, such as
gravity, friction, elastic, electric, push and pull,
centripetal forces
 The origins of these forces can be traced to only
four fundamental forces:




Gravity
Electromagnetic
Strong
Weak
Analyzing Forces
 A force is produced by an agent
 A force acts on an object – the receiver
 The force causes something to happen – the
effect
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Analyzing forces – Example 1
 Weight of boy (gravity):
Friction
 Agent – earth;
 Receiver – boy;
 Effect – boy slides downward.
Activity:
Identifying and Drawing Forces
Practice III.1 Force Challenge A-D
 Friction:
 Agent – surface of slide and
boy’s skin and clothes;
 Receiver – lower surface of
girl’s body;
 Effect – girl’s downward slide is
slowed down.
Weight
Forces studied in unit
 Four forces are studied in some detail:




Normal force
Gravitational force (lab)
Friction (lab)
Elastic force (lab)
Activity:
The Strength of Weight Lab
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Activity:
The Strength
of Elastic Force Lab
Activity:
The Strength of Elastic Force Lab
Experimental Results
Added
Mass
(g)
Spring
(cm)
Rubber
Band
(cm)
Bungee
(cm)
Added
Mass
(g)
Big spring Little Spring
(cm)
(cm)
0
54.1
35.9
55.1
0
15.5
13.9
100
56.4
38.2
55.7
10
19.5
15.9
200
60.5
41.5
56.1
20
23.7
17.9
300
64.4
46.5
56.5
30
27.7
19.8
400
68.6
53.6
57
40
31.8
21.7
500
72.8
57.7
57.5
50
35.9
23.7
600
76.8
61.2
58.8
60
39.8
25.6
700
81.2
63.3
61
70
43.5
27.6
800
85.4
64.5
63.5
80
47.7
29.7
900
89.6
65.3
65.6
90
51.5
31.4
1000
94
65.5
68.3
100
55
33.5
Experimental Results
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Mass (g)
Stretch (cm)
Conclusions
Drawing forces
 Force is directly proportional to stretch
 Slope of F vs stretch represents the strength of
the spring, k.
rise Fe
=
run !x
[F ] = N
[k ] =
[!x ] m
Normal
Weight
k = slope =
Normal
Weight
Normal
Weight
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Force Diagrams - Example 1
1. Picture
2. Identify System
Force Diagrams - Example 2
4. Identify contact forces where
system touches the closed curve.
7. Force
Diagram
5. Normal
force,FN
3. Closed curve
around system
6. Force of
gravity, FG
FN
FG
Force Diagrams - Example 2
Force Diagrams - Example 2
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Force Diagrams - Example 2
Force Diagrams - Example 2
Force Diagrams - Example 2
Force Diagrams - Example 3
7. Force
diagram
1. Picture
2-3. Define system and draw
closed curve around it.
4. Contact forces where system
touches curve
7. Force
Diagram
FN
5. (a)Normal
Force FN
5. (b)
Tension F T
FN
FT
Ff
FG
FT
6. Force of
gravity FG
FG
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Next steps...
 This unit then goes on to activities that connect
force to motion
 The next unit is Newton’s Laws
Contact info
[email protected]
[email protected]
www.physicsfirstmo.org
If you are a 9th grade teacher and are
interested in this program, please do
contact us - we plan to seek funding for
a new cycle.
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