Holding Up a Sign: Static Equilibrium Force and Torque

  • Thread starter PierceJ
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In summary, in order to keep the sign in static equilibrium, you would need to apply an external unknown vertical reaction force, V, and an unknown torque, T, at your hand. To solve for these, you would need to apply equilibrium equations and create a free body diagram.
  • #1
PierceJ
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Homework Statement


You are holding a sign as shown below. The sign (including the horizontal bar it hangs from) has a mass of 1.80 kg and is 36.5 cm wide. The sign is hanging from a 1.30 m tall, 4.16 kg vertical post. The sign is symmetric with a uniform mass distribution as implied by the drawing.
Q0vSIDa.png

What external force (+ if up, - if down) and torque (+ for CCW, - for CW) do you have to apply with your hand to keep the sign in static equilibrium? [Use g = 9.80 m/s2 and ignore the width of the vertical post.]

Homework Equations


Torque = Fd = 0

The Attempt at a Solution


I'm not quite sure how to deal with the vertical stick.
Torque = F1d1 - F2d2 - Fd3 = 0
As far as the set up goes, this is all I've got and I don't think it is correct. I may not be visualizing this problem correctly.
 
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  • #2
PierceJ said:

Homework Statement


You are holding a sign as shown below. The sign (including the horizontal bar it hangs from) has a mass of 1.80 kg and is 36.5 cm wide. The sign is hanging from a 1.30 m tall, 4.16 kg vertical post. The sign is symmetric with a uniform mass distribution as implied by the drawing.
Q0vSIDa.png

What external force (+ if up, - if down) and torque (+ for CCW, - for CW) do you have to apply with your hand to keep the sign in static equilibrium? [Use g = 9.80 m/s2 and ignore the width of the vertical post.]

Homework Equations


Torque = Fd = 0

The Attempt at a Solution


I'm not quite sure how to deal with the vertical stick.
Torque = F1d1 - F2d2 - Fd3 = 0
As far as the set up goes, this is all I've got and I don't think it is correct. I may not be visualizing this problem correctly.
There is an external unknown vertical reaction force and an unknown torque at your hand. You should identify these as V and T, respectively. Now apply your equilibrium equations to solve for them. Although explain what F1 ,d1 ,etc. are.
 
  • #3
How about starting with a free body diagram?
 

1. What is static equilibrium force?

Static equilibrium force refers to the balanced state of forces acting on an object, where the net force is equal to zero and the object is at rest or moving at a constant velocity.

2. How is static equilibrium force related to holding up a sign?

Holding up a sign requires the application of force to counteract the downward force of gravity. In order to maintain static equilibrium, the force applied must be equal and opposite to the force of gravity, resulting in a net force of zero and a sign that is not moving.

3. What is torque and how does it relate to holding up a sign?

Torque is the measure of the rotational force applied to an object. When holding up a sign, torque is created by the force applied to the sign multiplied by the distance from the point of rotation (such as the hand) to the point where the force is applied. This torque must be balanced in order to maintain static equilibrium and keep the sign from rotating.

4. How does the weight of the sign affect static equilibrium?

The weight of the sign, or the force of gravity acting on it, must be counteracted by an equal and opposite force in order to maintain static equilibrium. If the weight of the sign is too great, it may be difficult to hold it up without additional support or a larger force applied.

5. How can the principles of static equilibrium be applied in other situations?

The principles of static equilibrium, including balancing forces and torques, can be applied in various situations such as building structures, designing machines, and analyzing the stability of objects. It is an important concept in physics and engineering, and is used to ensure the safety and stability of many everyday objects and structures.

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