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Forces and FBDs

Forces and FBDs. A book is sliding rightward across a level table. Draw the FBD for the book. FBD: Example 2. A book is sliding rightward across a level table. Draw the FBD for the book. F N. F f. There is no applied force!. F g. Newton’s 2 nd Law of Motion: Student Learning Goal.

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Forces and FBDs

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  1. Forces and FBDs A book is sliding rightward across a level table. Draw the FBD for the book.

  2. FBD: Example 2 A book is sliding rightward across a level table. Draw the FBD for the book. FN Ff There is no applied force! Fg

  3. Newton’s 2nd Law of Motion: Student Learning Goal The student will be able to state Newton’s 2nd Law and apply it in qualitative and quantitative terms to explain the effect of forces acting on objects. (C3.3)

  4. Newton’s 2nd Law of Motion

  5. Newton’s Second Law of Motion If the net force on an object is not zero, the object will be accelerated in the direction of the net force.

  6. Newton’s Second Law of Motion If the net force on an object is not zero, the object will be accelerated in the direction of the net force.

  7. Newton’s Second Law of Motion If the net force on an object is not zero, the object will be accelerated in the direction of the net force. i.e. the more massive the object, the harder it is to change its motion (the higher its inertia).

  8. Newton’s Second Law of Motion If the net force on an object is not zero, the object will be accelerated in the direction of the net force.

  9. Weight The formula F = ma can also be used to calculate the weightFg of an object

  10. Weight The formula F = ma can also be used to calculate the weightFg of an object, the magnitude of the force of gravity acting on it

  11. Weight The formula F = ma can also be used to calculate the weightFg of an object, the magnitude of the force of gravity acting on it, if the acceleration a is . . .

  12. Weight The formula F = ma can also be used to calculate the weightFg of an object, the magnitude of the force of gravity acting on it, if the acceleration a is the acceleration due to gravity, g = 9.8 m/s2.

  13. Weight The formula F = ma can also be used to calculate the weightFg of an object, the magnitude of the force of gravity acting on it, if the acceleration a is the acceleration due to gravity, g = 9.8 m/s2. (mass is measured in kg)

  14. Weight Weight is therefore measured in Newtons. And the direction of the force is always [down].

  15. Newton’s 2nd Law: Example A weightlifter lifts a 160-kg weight by exerting a force of 1.8 kN [up]. The force of gravity on the object is 1.6 kN [down]. Draw a FBD of the weight. What is the net force on the weight? What is the acceleration of the weight?

  16. Newton’s 2nd Law: Example 1.8 kN 1.6 kN

  17. Newton’s 2nd Law: Example The net force is 0.2 kN [up]. 1.8 kN 1.6 kN

  18. Newton’s 2nd Law: Example What is the acceleration of the weight?

  19. Newton’s 2nd Law: Example What is the acceleration of the weight?

  20. Newton’s 2nd Law: Example What is the acceleration of the weight?

  21. Newton’s 2nd Law: Example What is the acceleration of the weight?

  22. Newton’s 2nd Law: Example What is the acceleration of the weight? The acceleration of the weight is 1.2 m/s2 [up].

  23. Example with the Equations of Motion A car is travelling at 25 m/s [forward] when the driver slams on the brakes and stops the car in 3.0 s. Calculate the acceleration of the car and the net force needed to cause that acceleration if the mass of the car is 1200 kg.

  24. Example with the Equations of Motion A car is travelling at 25 m/s [forwards] when the driver slams on the brakes and stops the car in 3.0 s. Calculate the acceleration of the car.

  25. Example with the Equations of Motion A car is travelling at 25 m/s [forwards] when the driver slams on the brakes and stops the car in 3.0 s. Calculate the acceleration of the car.

  26. Example with the Equations of Motion A car is travelling at 25 m/s [forwards] when the driver slams on the brakes and stops the car in 3.0 s. Calculate the acceleration of the car. i.e. 8.3 m/s2 [backwards]

  27. Example with the Equations of Motion Calculate the net force needed to cause that acceleration if the mass of the car is 1200 kg.

  28. Example with the Equations of Motion Calculate the net force needed to cause that acceleration if the mass of the car is 1200 kg.

  29. Example with the Equations of Motion Calculate the net force needed to cause that acceleration if the mass of the car is 1200 kg.

  30. Example with the Equations of Motion Calculate the net force needed to cause that acceleration if the mass of the car is 1200 kg.

  31. More Practice Homework Set 5: Newton’s 2nd Law of Motion

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