Differences between perturbation/variation of an object?

  • I
  • Thread starter troglodyte
  • Start date
  • #1
troglodyte
Gold Member
31
22
Hello Guys,

everyone use the word "perturbation" but no one explain it in a consist manner .So,If I perturb a system it is equivalent to vary a system?
Maybe someone can explain it to me in a clear way .

Thank You,
troglodyte
 
Last edited:

Answers and Replies

  • #2
dRic2
Gold Member
733
173
You perform a perturbation on a system if you change some parameters that define the state of the system. For example, imagine you are measuring the water flow rate outside of a tank. If you add some water to the tank or if you change the pressure inside the vessel, or if you change the dimension of the hole where the water flows out, you are perturbing the system which you were studying before and in fact the outcome of the new measurement (of the water flow rate) will be different from before.

In physics the world "perturbation" may also refer to the technique known as "perturbation theory".
 
  • Like
Likes troglodyte
  • #3
troglodyte
Gold Member
31
22
..which means through a perturbation of a system i change the state of system from an initial state to a final state.Therefore, to vary a system one needs a perturbation.So, both concepts are not not equivalent.There exist a kind of implication from perturbation theory to variational theory. Not vice a versa, right?
 
Last edited:
  • #4
troglodyte
Gold Member
31
22
I think one difference are the quantities which I perturb .In variational problems i perturb geometrical objects like curves ,areas..On the other hand ,in perturbation theory the perturbed objects are physical quantities of the systems, which I definitely know.
 
  • #5
anorlunda
Staff Emeritus
Insights Author
8,705
5,594
..which means through a perturbation of a system i change the state of system from an initial state to a final state.T
The perturbed state is not necessarily the final state.

Consider a ball initially at the bottom of a valley. We perturb it by moving it away from the bottom, then let go. In the final state it returns to the bottom. The goal of the problem might be to see whether or not it returns to the initial state.
 
  • Like
Likes troglodyte
  • #6
dRic2
Gold Member
733
173
in perturbation theory the perturbed objects are physical quantities of the systems, which I definitely know.
Hold on, I didn't say that perturbation theory is about perturbing stuff... In fact this is a pretty misleading way to put it. The word "perturbation" in "perturbation theory" has a different meaning. I just said that so that you don't confuse those terms but apparently it backfired
 
  • #7
FactChecker
Science Advisor
Gold Member
5,743
2,132
The term "variation" is generally used when there is a random component that causes random variations. The term "perturbation" is generally used there is a planned, hypothesized, or one-time, change to a system. But I do not think that there is an official rule that applies.
 
Last edited:
  • Like
Likes sophiecentaur
  • #8
sophiecentaur
Science Advisor
Gold Member
25,009
4,743
The term "variation" is generally used when there is a random component that causes random variations. The term "perturbation" is generally used there is a planned, hypothesized, or one-time, change to a system. But I do not think that there is an official rule that applies.
I think that makes sense and it's how I would look at things.
We're into that region of classification of terms again.
If you are searching then, rather than risk missing out on some information because the title / summary of a source may not be following the name convention, look deeper into any document before rejecting it merely on the basis of the use of one or other of those terms.
 
  • Like
Likes FactChecker
  • #9
troglodyte
Gold Member
31
22
look deeper into any document before rejecting it merely on the basis of the use of one or other of those terms.
Maybe you have a good reference.As I have stated before.The literature is not consistent in this case .Most of them uses the word "perturbation"but without introducing the concept and without telling what they concretely mean by this.
 
  • #10
FactChecker
Science Advisor
Gold Member
5,743
2,132
Maybe you have a good reference.As I have stated before.The literature is not consistent in this case .Most of them uses the word "perturbation"but without introducing the concept and without telling what they concretely mean by this.
So there is not a consistent use of the word. The next question is, what is the scenario in which you are seeing the word used? That should determine how it is being used.
 

Related Threads on Differences between perturbation/variation of an object?

Replies
1
Views
612
  • Last Post
Replies
3
Views
2K
  • Last Post
Replies
0
Views
2K
  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
1
Views
1K
  • Last Post
Replies
3
Views
3K
Replies
15
Views
3K
  • Last Post
Replies
4
Views
585
Replies
1
Views
2K
Replies
0
Views
1K
Top