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Thread: statics

  1. #1
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    statics

    statics-win_20170823_21_43_45_pro.jpg

    i am stuck on question 17.
    i am not sure on the direction on the forces and what forces are present.
    what is the difference between smoothly and free hinged ? is there x and y components for both. this is what I usually do to split up the normal reaction
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  2. #2
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    Re: statics

    Hey edwardkiely.

    What formulas do you have for the tension? [This is a mathematics forum per se - not a physics one].
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  3. #3
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    Re: statics

    Forces acting at point $a$ ... $N$ upward, $T_y$ upward, and $T_x$ to the right

    Forces acting at point $b$ ... equal reaction forces, $R$ to the left and right

    Force acting at point $c$ ... $N$ upward

    Force acting at the midpoint of $ab$ ... $W$ downward

    Forces acting at the midpoint of $bc$ ... $W$ downward, $T_y$ downward, and $T_x$ to the left.

    Geometry ... Vertex angle = $2\alpha \implies$ each base angle = $(90^\circ - \alpha)$. Also, note $\sin(90^\circ-\alpha)=\cos{\alpha}$


    $\displaystyle \sum F_y = 0 \implies N = W$


    $\displaystyle \sum \tau = 0$ about both rods ...

    Torques acting on rod $ab$ about point $b$ yields the equation ...

    $W\sin{\alpha} \cdot L + T_x \cos{\alpha} \cdot 2L = N\sin{\alpha} \cdot 2L + T_y \sin{\alpha} \cdot 2L$

    Torques acting on rod $bc$ about point $b$ yields the equation ...

    $N\sin{\alpha} \cdot 2L = W\sin{\alpha} \cdot L + T_y\sin{\alpha} \cdot L + T_x\cos{\alpha} \cdot L$

    Solve the system of torque equations for $T_x$ and $T_y$, then determine $T=\sqrt{T_x^2 + T_y^2}$
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  4. #4
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    Re: statics

    thanks.

    how do you know the normal reactions at c and a are the same by labeling them both N.?

    Also I am not sure why you do not take into account the vertical and horizontal components of the reaction at the hinge for letting forces up=forces down for the whole system?
    I understand why you do not take it into account when taking moments through b for the rods as you are taking moments about that point.
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  5. #5
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    Re: statics

    I will post it in advanced math topics
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    Re: statics

    Quote Originally Posted by edwardkiely View Post
    thanks.

    how do you know the normal reactions at c and a are the same by labeling them both N.?
    symmetry of the rod positions ... what would cause them to differ?

    Also I am not sure why you do not take into account the vertical and horizontal components of the reaction at the hinge for letting forces up=forces down for the whole system?
    there are no vertical forces acting on the hinge an point b ... the two rods push horizontally on each other at the hinge.
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  7. #7
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    Re: statics

    ok so the forces at the hinge cancel each other out.

    My last question is do you know what the difference between something that is freely hinged and smoothly hinged. I think smoothly means means the x and and y component of the normal reaction cancel out or something?
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