Why Do Dynamic and Static Methods Yield Different Tension Results?

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    String Tension
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Homework Help Overview

The discussion revolves around the differences in tension results obtained from dynamic and static methods while analyzing a toy pig suspended from a string. Participants explore the implications of these methods in the context of circular motion and tension forces.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • The original poster attempts to understand why the tension results differ between the dynamic and static methods. Questions are raised about the definitions of dynamic and static, as well as the reasons behind the discrepancies in tension measurements.

Discussion Status

Participants are actively engaging with the original poster's questions, offering clarifications and interpretations of the measurement methods. There is an ongoing exploration of the relationship between the measurements and the physical setup, with some participants questioning the assumptions made about the tension readings.

Contextual Notes

There is mention of a handout that describes the measurement process, which has led to confusion regarding the interpretation of the spring scale readings. Participants are also navigating the complexities of measuring tension in a dynamic system versus a static setup.

ys2050
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we hung a toy pig from the ceiling with a string and when turned on, it traveled in a circle.
We figured out the tension in the string using dynamic and static method...
in dynamic we just used the measured radius and found out the angle to calculate the force of tension.
in static, we measured the horizontal force by attaching the spring scale's hook to the hook where the string was hooked on. We pulled the apparatus horizontally to the radius. With this and the angle we calculated the force of tension.

My question is...
What is the difference in the result of the two methods?
Why is one called dynamic and the other, static?
Why do I get a slightly different tensions for the two methods?? What's the cause of the discrepancy?

Any help would be appreciated. :)
 
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ys2050 said:
… and when turned on …

in static, we measured the horizontal force by attaching the spring scale's hook to the hook where the string was hooked on. We pulled the apparatus horizontally to the radius.

Hi ys2050 :smile:

I love your flying pig! :smile:

(Did you ever work out why it wouldn't go backwards?)

Can you tell those of us who haven't seen it:

What do you mean by "turned it on" - where is the motor, and what does it do?

In the static case, I'm not getting it … what position did you pull the pig to, and what connection does that have to the dynamic case? :smile:
 
http://www.otherlandtoys.co.uk/flyingpig2_500.jpg
?
 
… just like in nature …

Thanx, acolavin! :smile:

ooh … I see it "has a realistic flying motion" …

hmm … how do they know? :smile:
 
tiny-tim said:
Hi ys2050 :smile:

I love your flying pig! :smile:

(Did you ever work out why it wouldn't go backwards?)

Can you tell those of us who haven't seen it:

What do you mean by "turned it on" - where is the motor, and what does it do?

In the static case, I'm not getting it … what position did you pull the pig to, and what connection does that have to the dynamic case? :smile:


I pulled the pig horizontally to its radius and the spring scale showed the horizontal force. I used that and the angle to figure out the tension of the string, which is the hypotenuse.
In the dynamic method, I used the formula T = mg / cos(theta)
In the static method, I used T = Fc / sin(theta), where Fc is the horizontal force.
and no... i still don't know why it can only fly in one way...
 
ys2050 said:
I pulled the pig horizontally to its radius and the spring scale showed the horizontal force. I used that and the angle to figure out the tension of the string, which is the hypotenuse...

No, the spring scale will show the tension in the string, not the horizontal componet.

CS
 
stewartcs said:
No, the spring scale will show the tension in the string, not the horizontal componet.

CS


but in the handout, it says:
" Holding the other end of the spring scale, horizontally pull it out to its radius when it was flying around in a circle. Note this reading down and calculate the tension in the string."

If the spring scale does measure the tension of the string, why would you need to do any calculation?!
 
ys2050 said:
but in the handout, it says:
" Holding the other end of the spring scale, horizontally pull it out to its radius when it was flying around in a circle. Note this reading down and calculate the tension in the string."

If the spring scale does measure the tension of the string, why would you need to do any calculation?!

If you pull on a string that is connected to a spring scale that is fixed to an articulated point, then the reading on the scale at that moment is the tension in the string.

However, I misunderstood what you were looking for. I believe that you are looking for the tension in the string the moment the pig was flying and trying to calculate it based on the tension you just measured in the horizontal direction while pulling the pig out to the radius of flight...right?

CS
 
Last edited:
… spring horizontal … ?

stewartcs said:
No, the spring scale will show the tension in the string, not the horizontal componet.

Ah, but I think ys2050 is holding the spring horizontally, so as not to interfere with the vertical component of the tension (so that it still matches the weight of the pig).

He therefore does measure only the horizontal component of the tension, and has to make a calculation to get the full tension.

Is that right, ys2050? :smile:
 
  • #10
tiny-tim said:
Ah, but I think ys2050 is holding the spring horizontally, so as not to interfere with the vertical component of the tension (so that it still matches the weight of the pig).

He therefore does measure only the horizontal component of the tension, and has to make a calculation to get the full tension.

Is that right, ys2050? :smile:

That's what I just said.

CS
 
  • #11
I think your previous response could be misinterpreted.
stewartcs said:
If you pull on a string that is connected to a spring scale that is fixed to an articulated point, then the reading on the scale at that moment is the tension in the string.
In the "static" case, the spring scale is attached to the pig, not the string on which the pig is hanging. So the scale reading is not the tension in the string (at least not that string).
 
  • #12
Doc Al said:
I think your previous response could be misinterpreted.

In the "static" case, the spring scale is attached to the pig, not the string on which the pig is hanging. So the scale reading is not the tension in the string (at least not that string).

Sorry, I thought I had made that clear by not mentioning a pig anywhere in the system.

The way I interpreted the measurement method was that the pig was removed and the spring scale was attached to the ceiling hook, then a string was attached to the spring scale and pulled to the radius of where the pig was flying.

I can't believe I'm talking about flying pigs. :smile:

CS
 
  • #13
stewartcs said:
The way I interpreted the measurement method was that the pig was removed and the spring scale was attached to the ceiling hook, then a string was attached to the spring scale and pulled to the radius of where the pig was flying.
Perhaps it wasn't clear from this thread (he has another thread on the same topic :mad:), but he's measuring the same tension via two different methods. In both methods, the pig is there.
I can't believe I'm talking about flying pigs. :smile:
You've got to believe!
http://keithcombs.members.winisp.net/flyingpig.gif
 
Last edited by a moderator:
  • #14
… ooh look … there's another one … !

stewartcs said:
The way I interpreted the measurement method was that the pig was removed …

A flying pig without the pig … is like a grin without the cheshire cat! :biggrin:

Never ignore the flying pig!

Those who ignore flying pigs …

:smile: are pig-ignorant! :smile:​
I can't believe I'm talking about flying pigs. :smile:

Would you believe … they're talking about you? :smile:
 

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