How to calculate the perpendicular tension?

In summary, The problem being discussed is about determining the tension of a cable perpendicular to a bar with a weight on top, using the principle of moments. The solution involves doing force balances at the point where the rod meets the rope and assuming that the rod can only exert a force along its length. Other concepts that may be useful to learn include the principle of moments and how to handle forces acting along the beam.
  • #1
jorgeha
12
1
Hello to everyone, merry christmas and happy new year! I was trying some exercises on the Feynman Lectures, on the topic of statics, and I came across with a problem which, simplified until where I am stuck, asks for the tension of a cable perpendicular to a bar with a weight on the top of it, as in the picture below. I don't know which trigonometrical function should I use, as the force going downwards y-axis is perpendicular to the tension on the x-axis, the tension seems to be 0! (That is obviously incorrect) Should I first calculate the force going down the bar, and then multiply it by the angle θ?
https://postimg.org/image/5401ebhg3/
Thanks for reading and answering!
 

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  • #2
Have you heard of balance of moments?
 
  • #3
Chestermiller said:
Have you heard of balance of moments?
Sadly, I haven't. I am studying with the Lectures and it isn't a very complete book (I mean, it isn't like a textbook). With the balance of moments, which other concepts do you think I should learn? Can you show me how to do it anyways? Thanks
 
  • #4
Rather than trying to understand some cobbled-together explanation from a PF member, it would be good if you look up "The principle of Moments" in an on-line text and look at some worked examples. It's a very basic bit of book work and you will find it in many places. The very basic approach is to study the see saw, with all the forces acting up or down, at right angles to the beam. The next step is to have forces that are acting in a general direction (which is like your problem)
This link is just one of many that have the answer to how to work out your prob.
 
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  • #5
It is possible to do this problem without using a moment balance. You do force balances on the point where the rod meets the rope. The trick is to assume that the rod can exert a force only in the direction along its length.
 
  • #6
sophiecentaur said:
Rather than trying to understand some cobbled-together explanation from a PF member, it would be good if you look up "The principle of Moments" in an on-line text and look at some worked examples. It's a very basic bit of book work and you will find it in many places. The very basic approach is to study the see saw, with all the forces acting up or down, at right angles to the beam. The next step is to have forces that are acting in a general direction (which is like your problem)
This link is just one of many that have the answer to how to work out your prob.
Thank you very much for your answer. Do you know any other important concept I should learn? I will study that principle tomorrow :). I am studying with the Lectures, and they aren't like a textbook, I don't know which particular concepts I must know... do you know any other which will be useful for me? Thank you!
 
  • #7
Chestermiller said:
It is possible to do this problem without using a moment balance. You do force balances on the point where the rod meets the rope. The trick is to assume that the rod can exert a force only in the direction along its length.
Thanks, that was my doubt!
 
  • #8
Chestermiller said:
It is possible to do this problem without using a moment balance. You do force balances on the point where the rod meets the rope. The trick is to assume that the rod can exert a force only in the direction along its length.
That's true in this case but it only works when all forces are applied to the same point at the end of a beam. Moments are very relevant in most cases and it is good to be able to tackle all problems in the same way - at least until you are very familiar with the whole business. Also, forces acting along the beam can be ignored when you use Moments.
 
  • #9
sophiecentaur said:
That's true in this case but it only works when all forces are applied to the same point at the end of a beam. Moments are very relevant in most cases and it is good to be able to tackle all problems in the same way - at least until you are very familiar with the whole business. Also, forces acting along the beam can be ignored when you use Moments.
The forces along the beam have zero moment arm, so their moments are zero.
 
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FAQ: How to calculate the perpendicular tension?

1. How do I calculate the perpendicular tension in a system?

The perpendicular tension in a system can be calculated by using the formula T = Fsinθ, where T is the perpendicular tension, F is the applied force, and θ is the angle between the force and the direction of perpendicular tension.

2. What is the significance of calculating perpendicular tension in a system?

Calculating perpendicular tension is important in understanding the forces acting on a system, and can help determine if the system is in equilibrium or not. It is also useful in designing structures and predicting their stability.

3. Can the perpendicular tension be negative?

Yes, the perpendicular tension can be negative if the applied force and the direction of tension are opposite to each other. This indicates that the force is pulling the system in the opposite direction of the tension.

4. How can I measure the angle θ for calculating perpendicular tension?

The angle θ can be measured using a protractor or by using trigonometric functions if the lengths of the sides of the triangle formed by the force and the perpendicular tension are known.

5. Is there a limit to the magnitude of perpendicular tension in a system?

There is no specific limit to the magnitude of perpendicular tension, as it depends on the applied forces and the properties of the system. However, excessive tension can cause structural failure, so it is important to carefully consider the forces and their effects on the system.

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