1. Demystifying the Mystery of Action-Reaction Forces HS SCIENCE CONCEPT PRESENTATION July 2010 Bianca Mercuri

2.  Background Information  Overview of the Law  Ministry Expectations  Practical Applications  Curriculum Sequence  Learning Difficulties  Lesson Sequence  Assessment & Evaluation Suggestions  Safety Considerations  Resources

5.  COURSE: SPH 3U  UNIT: 2 – Forces  KEY UNDERSTANDINGS: Conceptual and mathematical problem-solving Newton’s 3 rd law is one of the course’s the most difficult concepts for students to understand!!!

6. Can be taught in two main ways: 1. For every action there is an equal but opposite reaction (F A = -F B ) 1. Whenever one object exerts a force on a second object, the second object exerts a force that is equal in magnitude and opposite in direction back onto the first object. Which one do you think may cause misunderstanding among our students? Why?

7. Big Ideas  Forces - Forces can change the motion of an object. Applications of Newton’s laws of motion have led to technological developments that affect society and the environment. Overall Expectations  C1. analyze and propose improvements to technologies that apply concepts related to dynamics and Newton’s laws, and assess the technologies’ social and environmental impact;  C2. investigate, in qualitative and quantitative terms, net force, acceleration, and mass, and solve related problems;

8. Specific Expectations  C2.1 use appropriate terminology related to forces, including, but not limited to: mass, time, speed, velocity, acceleration, friction, gravity, normal force, and free-body diagrams  C2.2 conduct an inquiry that applies Newton’s laws to analyse, in qualitative and quantitative terms, the forces acting on an object, and use free-body diagrams to determine the net force and the acceleration of the object  C3.2 explain how the theories and discoveries of Galileo and Newton advanced knowledge of the effects of forces on the motion of objects  C3.3 state Newton’s laws, and apply them, in qualitative terms, to explain the effect of forces acting on objects

9. Virtually all motion is dependent on Newton’s 3 rd law  Jumping, walking, running  Driving, riding a bike  Swimming, canoeing  A bird or helicopter flying  A jet engine or rocket http://dsc.discovery.com/videos/time-warp-water-rocket.html

10. Newton’s 3 rd law is the quintessential culminating topic for the first two units, most importantly the second unit on dynamics

11. Two Main Categories of Difficulty: 1) Conceptual Understanding – Thinking differently i. Free-body diagrams ii. Concept questions (question their “beliefs”) 2) Mathematical Problem-Solving i. Scaffolding ii. Practice, practice, practice!

12. MISUNDERSTANDING: “Action-reaction forces act on the same body, so why does anything ever move? TRUTH: They actually act on different bodies. SOLUTIONS: Free-body, free-body, free-body! 1) Draw FBD of various action reaction pairs 2) Concept questions on action-reaction pairs 3) Correct definition

13. 1) Drawing FBD of action-reaction pairs requires not one FBD, but TWO!

14. 2) Concept questions on action-reaction pairs Which of the following force pairs is/are not an action-reaction pair? a)the force you exert on the earth as you stand in your house and the force that the floor of the house exerts on you b) the force a bat exerts on a baseball and the force the baseball exerts on the bat c) the force a finger exerts on a button and the force the button exerts on the finger d)None of the above; a, b, and c are action-reaction pairs. e) b and c contain force pairs that are NOT equal to each other even tough they are opposite in direction.

15. For every action there is an equal but opposite reaction (F A = -F B ) or Whenever one object exerts a force on a second object, the second object exerts a force that is equal in magnitude and opposite in direction back onto the first object. 3) Correct Definition

16. MISUNDERSTANDING: “The action force comes first and is separate from the reaction force. Each force can be clearly defined.” TRUTH: Both forces are the action and the reaction as they occur at the same time. SOLUTION: Question their “beliefs”?  Use in-class demos, video clips and real life situations and ask “Which came first?”

17. MISUNDERSTANDING: “Only animate objects exert forces; inanimate objects (i.e. tables, floors) don’t” TRUTH: All objects exert force, no matter the nature. SOLUTION: Question their “beliefs”?  “How do you stay on your chair?”, “Do you feel the wind?”, “Do you feel the book on top of your head?”

18. MISUNDERSTANDING: “Larger objects exert more force than a greater object”. (i.e. the Earth exerts a greater force on you than you do on it) TRUTH: Both objects exert the same amount of force. The effect of the force is different on each object due to Newton’s 2 nd law. SOLUTION: Vernier Probe-ware Demonstration  Probe-ware demo shows evidence of truth

20. MISUNDERSTANDING: Mathematical solving of action-reaction problems. TRUTH: It’s tricky and it takes a lot of practice. SOLUTION: Scaffolding  Start with high level of scaffolding for various problem types and slowly reduce with time and practice.

21.  Scaffolding via chalk & talk  Scaffolding reference/worksheets  Variety of questions  Practice, practice, practice! Ok, now you try!

22. 1) Pay attention & Warning! 1) Definitions and practical uses (student brainstorm) 1) Demos (in-class & video clips) 1) Scaffold base problem as class (Socratic) 1) Small group/individual problem solving using scaffold 1) Assessment of one problem prior to leaving 1) HOMEWORK: Concept questions, base problems

23. 1) Math and concept issues (student driven) 1) More demos to help concept understanding? 1) Scaffold more complex problems with gravity and friction (Socratic) 1) Small group/individual problem-solving of more complex problems using scaffold 1) Assessment of one problem prior to leaving 1) HOMEWORK: More complex problems

24. 1) Math and concept issues (student driven) 1) Action-Reaction lab  Action-reaction carts or Vernier probe-ware  Possible A&E through an informal lab report with PR, AI, C as well as problem solving/calculations

25. “AS” & “FOR” Learning 1) Question period, walk around, Socratic method 2) G.R.A.S.S. assessment of one problem prior to leaving HS Science/Concept Presentation/G.R.A.S.S. Assessment.doc HS Science/Concept Presentation/G.R.A.S.S. Assessment.doc “OF” Learning 1) Concept and/or problem-solving quiz 2) Action-Reaction lab

26.  Physical demos  Computer equipment

27. Physical/In-Class Demos:  Action-reaction carts  Scooter-boards and medicine ball  Fan-powered vehicle Technology:  Video clips  Probe-ware  Simulations (gizmos, esamultimedia.esa.int)

28. http://esamultimedia.esa.int/docs/issedukit/en/ht ml/t0205e1.html

29. Labs/Activities:  Using action-reaction carts  Using probe-ware Handouts:  Scaffolding worksheet  Concept questions  Math problem-set  G.R.A.S.S. assessment template