I am doing physics AS again but...............

[Just call me MJ]

I did physics As last year and my teacher made me study the addition of parallel and series springs.
I am confused because I bought the new book and it didn't have this topic! So should I study it or should I just leave it behind?!?

 

[Doctor Nemo]

I did physics As last year and my teacher made me study the addition of parallel and series springs.
I am confused because I bought the new book and it didn't have this topic! So should I study it or should I just leave it behind?!?

Parallel and series springs is not really a distinct topic. Having two identical springs in parallel means that the weight is divided between them, so their extension 1/2 that of a single spring. When they are in series each spring is subjected to the same force so each will have the extension as when there is only one spring.

However two springs in parallel is the same as doubling the cross-sectional area of a wire and asking how that will affect its extension. Two springs in series is the same as doubling the length of a wire and asking how that will affect the extension. This is in the syllabus and is a very common question on paper 1.

So to answer your question, yes you have to understand them because they are no different from wires.

See question 21, paper 1, November 2008.

 

[Just call me MJ]

first things first! Thanks for the quick reply!
what if the springs were of different lengths in the parallel arrangement?
and what if the wires are made of two different materials? like gold and copper? (this question is for both parallel and the series)
can you please help me out with this? cause is the only topic in physics that I didn't cover or understand!
Thank you for your time, in advance.

 

[Doctor Nemo]

first things first! Thanks for the quick reply!
what if the springs were of different lengths in the parallel arrangement?
and what if the wires are made of two different materials? like gold and copper? (this question is for both parallel and the series)
can you please help me out with this? cause is the only topic in physics that I didn't cover or understand!
Thank you for your time, in advance.

If the two springs were not made of the same material or of the same length then they would have different spring constants. Analysis of parallel springs requires that the springs be identical otherwise the situation becomes too complicated and is not likely to appear on an AS exam.

However in the series situation the two springs act independently of each other and you can analyze the situation by finding the extension of each and adding them together.

Springs or wires merely transmit force. For example suppose one spring stretched x with a 4 N force and a second spring stretched 2x. If hung in series with a weight of 4 N then the total extension would be 3x because both springs are subjected to a force of 4 N.

The spring on the bottom feels the 4 N force of the weight. It doesn´t “know” whether it is attached to another spring or just to a support. If it is attached to a support it would exert a 4 N force down (the same magnitude and direction as the weight) on the support (and the support a 4 N force on the spring). This must be the case or the forces would not be balanced on the spring and it would accelerate.

The top spring feels a force from the bottom spring of 4N. It doesn´t “know” whether that force is from a spring or a weight.

Springs and wires only transmit force. Whatever force is exerted on a spring that spring will simply transmit that force (with the same magnitude and direction) to its support.

 

[sweetiepie]

I did physics As last year and my teacher made me study the addition of parallel and series springs.
I am confused because I bought the new book and it didn't have this topic! So should I study it or should I just leave it behind?!?

http://www.xtremepapers.com/community/threads/some-different-notes-website-are-available.10423/ u can get sum help frm here

 

[Just call me MJ]

that was helpful. thanks! but I am affraid that I am going to bother you with a few more questions about this topic.....
What if the weight of the load was not suspended in the middle of the two parallel springs?
lets say we have spring A and spring B, which are identical. The distance between the load and spring A is shorter than that between the load and spring B! how do we deal with this? do we deal with it as a ''moment of a force''?
and please post a few equations that I can use.
thanks

 

[Doctor Nemo]

that was helpful. thanks! but I am affraid that I am going to bother you with a few more questions about this topic.....
What if the weight of the load was not suspended in the middle of the two parallel springs?
lets say we have spring A and spring B, which are identical. The distance between the load and spring A is shorter than that between the load and spring B! how do we deal with this? do we deal with it as a ''moment of a force''?
and please post a few equations that I can use.
thanks

In that situation there are not only moments but torque. The side with spring A would tend to move down and the side B tend to would move up. I have some difficulties in picturing what the equilibrium of the system would be like, I think you would need to take into account the weight of the beam itself. Perhaps you can have your teacher do a demonstration. Whatever the outcome it would involve solving for how much the beam moves from the horizontal as well as the extensions of the springs. This looks again too complicated to be included in the range of the AS syllabus.

There was a question somewhat like this on paper 2 of June 2002. However in that question it was really only about moments because they made the assumption that the beam would remain horizontal.

Formulas, everyone wants formulas. If only all the problems of life could be solved with mathematical formulas. Thus so with physics. I will try to post some formulas with explanations later when I have more time.

 

[Doctor Nemo]

If I have attached the file correctly then here are the formulas and relationships. Do not just memorize them, try to understand them.

 

[Just call me MJ]

If I have attached the file correctly then here are the formulas and relationships. Do not just memorize them, try to understand them.

Thank you very much! And I am sorry for all the trouble!!

 

[Doctor Nemo]

Thank you very much! And I am sorry for all the trouble!!

It was a pleasure, I enjoyed thinking about your questions. I hope the document I posted helps you with your doubts. Try doing the second part of problem 4, paper 2 June 2009 to see if you understand the different arrangements of springs and post any further doubts that occur to you.