Introduction to Free Body Diagrams

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Introduction to Free Body Diagrams

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  1. Free Body Diagrams(FBD’s)

    Slide 1 - Free Body Diagrams(FBD’s)

    • Mr. Weisenfeld
  2. Definition

    Slide 2 - Definition

    • Free body diagrams (otherwise known as FBD's) are simplified representations of an object (the body) in a problem, and includes force vectors acting on the object. This body is free because the diagram will show it without its surroundings; i.e. the body is 'free' of its environment. This eliminates unnecessary information which might be given in a problem.
  3. Force of Gravity:

    Slide 4 - Force of Gravity:

    • The first force we will investigate is that due to gravity, and we'll call it the gravitational force.
    • We know that the acceleration due to gravity (if on Earth) is approximately
    • This gravity force, by Newton's Second Law is
    • This can also becalled weight, or
    • Try not to get confused. One is meters, the other is mass in kilograms.
  4. Normal* Force:

    Slide 6 - Normal* Force:

    • The normal force one which prevents objects from 'falling' into whatever it is they are sitting upon.
    • It is always perpendicular to the surface with which an object is in contact. For example, if there is a crate on the floor, then we say that the crate experiences a normal force by the floor; and because of this force, the crate does not fall into the floor.
    • The normal force on the crate points upward, perpendicular to the floor.
    • *Normal here is used in the sense of perpendicular.
  5. Finish the Statement…

    Slide 7 - Finish the Statement…

  6. Friction Force:

    Slide 8 - Friction Force:

    • Related to the normal force is the frictional force.
    • The two are related because they are both due to the surface in contact with the body. Whereas the normal force was perpendicular to the surface, the frictional force is parallel.
    • Furthermore, friction opposes motion, and so its vector always points away from the direction of movement.
    • Friction force is the buildup of tiny microscopic peaks and valleys that are being force to slide against each other.
  7. Applied Force:

    Slide 10 - Applied Force:

    • Finally, we get to the physical push or pull that is directly being done to the object.
    • A push with your hands or with a stick would be drawn the same as a pull with a rope or a handle.
    • If the pull is done with a rope we talk about the tension in the rope, or .
    • Notice that the free body diagram would be the same if is a push or a pull to the right.
  8.  Net Force:

    Slide 12 - Net Force:

    • The net force or the unbalanced force is the vector sum of all the forces which act upon an object.
    • That is to say, the net force is the sum of all the forces, taking into account the fact that a force is a vector and two forces of equal magnitude and opposite direction will cancel each other out.
    • A vector sum means that a vector in one direction is positive and a vector in the opposite direction is negative.
  9. Let’s go over the Worksheet, Please Grade Your Own!

    Slide 14 - Let’s go over the Worksheet, Please Grade Your Own!

    • Click next when you are ready to get started!
  10. Slide 15

    • Does
  11. Slide 16

    • Does
  12. Slide 17

    • Does
  13. Slide 18

    • But first …
  14. Slide 20

    • Does
  15. Slide 21

    • Does
    • Forces Labeled +4/4
    • Up down Forces equal +2/2
    • Left Right forces Net Right +2/2
    • Total Points 8/8
  16. Slide 22

    • Does
    • 4 Forces labelled: +4/4
    • Up Down Forces equal: +2/2
    • Left Right forces equal: + 2/2
    • Total Points = 8/8
  17. Slide 23

    • Does
    • Up-down Forces labelled: +2/2
    • The sizes of the Forces equal: +2/2
    • Total points + 4/4
  18. Slide 24

    • Does
  19. Slide 25

    • Does
  20. Slide 26

    • Does
    • Gravity force drawn: +1
    • Magnitude of force and units: +1
    • Total Points +2/2
  21. Slide 27

    • Does
  22. Please mark total correct out of

    Slide 28 - Please mark total correct out of

    • Bottom right, thanks!
    • Then put in the gray tray near the door, thanks!