How Do I Find Direction of Forces in Statics?

  • Thread starter Ivan Antunovic
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In summary, the direction of forces S1, S2, and S3 in the given diagram is arbitrary. It is important to define a consistent direction as it will affect the equations used to find the unknown forces. In this case, the forces may be either compressive or tensile depending on the chosen direction. It is necessary to use the equations of statics to determine the magnitude and direction of these forces. The second picture, although uploaded in reverse, can still be used for analysis in the same way as the first picture.
  • #1
Ivan Antunovic
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I really don't understand what is the logic in the direction of forces S1,S2 and S3.This is an example and here are given directions of the forces,but in the exam I will have to find them on my own.
Could someone explain to me how should I find them and what kind of thinking I have to apply here,maybe action equals minus reaction ?
I really have a bad professor from Mechanics and she just doesn't care to explain very much.

Thank you in advance I hope pictures are clear.
 

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  • #2
The last picture...don't know why it wasnt uploaded in the first post
 
  • #3
Ivan Antunovic said:
The last picture...don't know why it wasnt uploaded in the first post
 

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  • #4
Ivan Antunovic said:
I really don't understand what is the logic in the direction of forces S1,S2 and S3.This is an example and here are given directions of the forces,but in the exam I will have to find them on my own.
Could someone explain to me how should I find them and what kind of thinking I have to apply here,maybe action equals minus reaction ?
I really have a bad professor from Mechanics and she just doesn't care to explain very much.

Thank you in advance I hope pictures are clear.
I think the direction of the forces as shown on the diagram is arbitrary. You can assume that the direction indicates, for example, a compressive force in each rod.

After you work out the forces in each rod which keep this system in statics equilibrium, there may indeed be forces which are in tension, that is, which will tend to pull a rod out of the wall.

It's hard to figure out what is the true case here just by inspection. The rods appear to be symmetrical with respect to the y-axis.

As always, use the equations of statics to find the unknown force magnitudes in each of the three rods.
 
  • #5
In general if a problem statement doesn't define which direction is +ve then you have to do so. You can make an arbitrary choice but you must be consistent. eg you have to take that into account when you are writing your equations (eg when summing components of forces or torques). The answer force(s) or torque(s) will turn out to be +ve or -ve then you refer to your definition of +ve to work out which direction it points and calculate any angles appropriately.
 
  • #6
CWatters said:
In general if a problem statement doesn't define which direction is +ve then you have to do so. You can make an arbitrary choice but you must be consistent. eg you have to take that into account when you are writing your equations (eg when summing components of forces or torques). The answer force(s) or torque(s) will turn out to be +ve or -ve then you refer to your definition of +ve to work out which direction it points and calculate any angles appropriately.

So I could basically take directions as I've taken on this picture and it should be fine?
 

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  • #7
Sorry for the 2nd picture being reverse uploaded tried to upload it again normally but failed.
 

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Related to How Do I Find Direction of Forces in Statics?

1. What is "The problem with Statics"?

"The problem with Statics" refers to the concept in physics that states that an object at rest will remain at rest unless acted upon by an external force. This poses a challenge in understanding the motion and stability of objects, as it goes against our everyday experience of objects coming to rest on their own.

2. How does the problem with Statics affect real-world scenarios?

Understanding the problem with Statics is crucial in many real-world scenarios, such as designing structures or machines. Without taking into account external forces, a structure or machine may not be able to withstand the forces acting upon it, leading to potential failure or collapse.

3. What are some common misconceptions about the problem with Statics?

A common misconception is that objects only move when a force is applied to them. In reality, objects can also move due to internal forces, such as friction or gravity. Another misconception is that an object at rest has no forces acting upon it, when in fact there may be multiple forces acting in different directions that cancel each other out.

4. How can one overcome the problem with Statics?

To overcome the problem with Statics, one must consider the various forces acting upon an object and their direction and magnitude. By using tools such as free body diagrams and applying the laws of motion, one can accurately analyze the motion and stability of an object.

5. Are there any real-life examples of the problem with Statics?

Yes, there are many real-life examples of the problem with Statics, such as the leaning Tower of Pisa. The tower is able to remain standing despite its noticeable tilt because the forces acting upon it are balanced. However, even a small external force could cause it to topple over due to the problem with Statics.

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