/Interface08Intro%20Forces by Meera Chandrasekhar

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

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

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

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

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

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)

54.1

35.9

55.1

15.5

13.9

100

56.4

38.2

55.7

19.5

15.9

200

60.5

41.5

56.1

23.7

17.9

300

64.4

46.5

56.5

27.7

19.8

400

68.6

53.6

31.8

21.7

500

72.8

57.7

57.5

35.9

23.7

600

76.8

61.2

58.8

39.8

25.6

700

81.2

63.3

43.5

27.6

800

85.4

64.5

63.5

47.7

29.7

900

89.6

65.3

65.6

51.5

31.4

1000

65.5

68.3

100

33.5

Experimental Results

Mass (g)

Stretch (cm)

Conclusions

Drawing forces

ď Ż Force is directly proportional to stretch ď Ż 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

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

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

5. (a)Normal Force FN

5. (b) Tension F T

Ff FG

FT 6. Force of gravity FG

Next steps...  This unit then goes on to activities that connect force to motion  The next unit is Newton’s Laws

Contact info MeeraC@Missouri.edu KosztinD@Missouri.edu 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.