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5 Newton’s Third Law of Motion

5 Newton’s Third Law of Motion. Force inter actions & Newton’s 3 rd Law Systems Vectors, Components & Vector Addition Homework: RQ: 4, 5, 10, 11, 12, 13, 15, 17, 20, 21. Ex: 13, 22, 30, 38, 39, 43, 44, 45, 48. Problems: 1, 2, 3, 4. Forces and Interactions. inter = between

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5 Newton’s Third Law of Motion

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  1. 5 Newton’s Third Law of Motion • Force interactions & Newton’s 3rd Law • Systems • Vectors, Components & Vector Addition • Homework: • RQ: 4, 5, 10, 11, 12, 13, 15, 17, 20, 21. • Ex: 13, 22, 30, 38, 39, 43, 44, 45, 48. • Problems: 1, 2, 3, 4.

  2. Forces and Interactions • inter = between • all forces are interactions between masses • each mass feels same size force

  3. Newton’s 3rd Law of Motion • Whenever one object exerts a force on a second object, the second object exerts an equal and oppositely directed force on the first.

  4. Systems • (net-external force on a system) = (mass of system)x(acceleration of system). • often defined so unknown forces can be determined, e.g., tension can be determined below.

  5. What external forces act on this system? Can the system move?

  6. What forces act on the man?Draw a Force Diagram for him.

  7. Summary of Newton’s Laws • 1st: Fnet = 0  constant velocity • 2nd: Fnet = ma • 3rd: Forces occur in pairs (equal size, opposite direction)

  8. Newton’s 3rd Law Pair Notation • use “x” marks on forces that are 3rd Law pairs. • Remember: There will never be two “x” marks on one motion diagram. • The other “x” will be on force diagram of other object. • Use “xx” for a different interaction, etc.

  9. Force Diagram each object. Which has greater acceleration when released?

  10. Pract. Physics: Page 21 #2(at bottom)

  11. Vector Addition • addition is done tail-to-head, also called “parallelogram rule” • added to determine net force • if net force is known, we use vector addition to determine components, e.g. lantern hanging from two ropes. • //

  12. Which strings have greater tension?

  13. Add Velocities to Find Speed & Direction

  14. Diagonal of Square is 1.41 times its sides

  15. 3-4-5 Rule

  16. Components of Vectors • component = part • horizontal part is the “x component” • vertical part is the “y component”

  17. Practical Vector Addition

  18. Summary • All forces are interactions, i.e., part of a pair of forces • Newton’s 3rd Law: pairs have equal size opposite direction • Systems are defined to determine unknown forces • Vectors, Vector Components, Parallelogram Rule

  19. Practicing physics • Do Page 27 • Refer to page 26 to review parallelogram rule of vector addition

  20. Action and Reaction

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