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Forces and Angles

Forces and Angles. Physics 11. More bad jokes…. Review: Free-body diagrams:. Free-body diagrams are used to show the relative magnitude and direction of all forces acting on an object. What if some of the forces were not in the x or y plane???????. Forces at angles:.

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Forces and Angles

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  1. Forces and Angles Physics 11

  2. More bad jokes…

  3. Review: Free-body diagrams: • Free-body diagrams are used to show the relative magnitude and direction of all forces acting on an object. • What if some of the forces were not in the x or y plane???????

  4. Forces at angles: • We will break the forces with angles into their x and y components using trigonometry!

  5. Review: Fnet • Remember we are only worried about Fnet in the direction of the motion • So sometimes we really only need either the x or y component of the force at an angle.

  6. Example 1: • You need to move a 25.5 kg wooden crate across a wooden floor (µ=0.20). You pull with a rope attached at a 15º to the horizontal with a force of 276N. • Calculate the Fapp(X) and Fapp(Y). • What is the acceleration of the crate?

  7. a. Fapp(x)= 276 N * cos 15 = (276)(0.9659) = 267 N Fapp(y)= 276 N * sin 15 = (276)(0.2588) = 71.4 N =15º

  8. b. • FBD • Only need to consider x axis forces as that is the plane of the motion. • Ff = µFN = (0.20)[(25.5)(9.81) = 50.0 N • Fnet= Fapp(x) + Ff = 267N – 50N = 217 N Fnet= ma 217= (25.5)a 8.5 m/s2= a

  9. Is it easier to push or pull a sled?

  10. Pulling a Sled • A child of 35kg is sitting on a sled that has a coefficient of kinetic friction of 0.10 with the snow. If the parent who is pulling the sled pulls up with an angle of 25°, with what are the component forces? • Draw FBD

  11. FBD FN Fa Ff Fg

  12. Break Applied Force into Components Fa Fay Fax

  13. Example: Pushing a Sled • A child of 35kg is on a sled that has a µk =0.10 with the snow. If the parent who is pushing the sled pushes down with an angle of 25°, with what are the component forces. • Draw FBD.

  14. FBD FN Fa Ff Fg

  15. Break Applied Force into Components Fax Fay Fa

  16. Practice: • Force Components: Vectors WS • Do 5d and 6c together • Page 171 #11, 12 (assume no Ff) • Page 208 # 24, 25

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