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Force Body Diagram

  1. Oct 31, 2013 #1

    I have been assigned a project to find a device to improve on, and one of the tasks is to create a force body diagram. I have a little bit of confusion when it comes to drawing it because if I'm writing the paper on shoes, and how it improves the movement of the feet, how will the free body diagram look?

    I understand that in able for your whole body to move, you have to consider the frictional force, applied force, and the normal force. Does that include the forces exerted from the ground?

    Also if you were to focus the force body diagram primarily on the feet, what would the forces be applied when you are walking/running? Would the forces change depending on the structure of the shoe that is being worn? How would you get the magnitudes of the forces?

    Please help!
  2. jcsd
  3. Oct 31, 2013 #2

    Simon Bridge

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    Welcome to PF;
    Your choice of device should be appropriate to the assignment - so if you don't know how to do a free-body diagram for it, it is probably not a good choice. Notice also that you have been asked to improve on it - how would you use knowledge of forces to improve on the design of a shoe?

    See what I mean?

    Anyway - a fbd for a foot would be a spot, with arrows for all the forces on a foot in the situation you are interested in. "movement" is too vague to investigate - which movement in particular?
  4. Nov 1, 2013 #3
    Thank you for the welcome.

    Well, I was planning on the improving the shoe in a way to promote forefront strikes (running on the balls of your feet instead of the heel). I have read that common modern shoes are constructed with elevated heels that protects it, but also promotes a running technique that applies a relatively stronger force onto your heel, that causes pain and injury. I wanted to know if it was possible to incorporate that "force" within the feet's force body diagram?

    For movement, I was referring to the foot as it runs in a straight direction.
  5. Nov 1, 2013 #4

    Simon Bridge

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    OK - running motion is quite complicated too. Which part of the running motion are you after?
    See if you can isolate the part of the motion that you are interested in - the bit where the elevated heel affects the way you run.

    I still think you have chosen an inappropriate subject for your study.
  6. Nov 1, 2013 #5
    Just the moment the foot is contact with the ground.

    Ahhh I was hoping no one would say that... What are you suggesting?
  7. Nov 1, 2013 #6

    Simon Bridge

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    OK - so draw a detached foot on the ground.
    What are the forces on it?

    I think you are still not simple enough but you'll figure that out.

    Not suggesting anything - I'm saying it directly.

    You'll find out as you draw the foot - the forces act on different parts of the structure of the foot in different directions. You may need to consider the effect of the bone structure as well as the flesh and skin as padding - then there are the various shoes themselves so you can see how the forces balance out.

    Then you need to bear in mind that this is a dynamic system - not a static one. The foot is accelerating at that time - going from a downward motion to an upwards one (with forward and lateral horizontal components also changing).

    But if you are enjoying yourself keep going.
    By breaking a complicated problem down into it's components you'll learn a lot.

    Having explored a bit - you need to refine your actual question for study.
    What, exactly, is the problem you are trying to solve?
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