An Experiment To Examine the Effect of Springs In Parallel

AN EXPERIMENT TO EXAMINE THE EFFECT OF

SPRINGS IN PARALLEL

I am going to set up an experiment to see what happens to the extension of springs that are all the same size and material in parallel. I will use identical springs and in parallel they will look like this:

I am going to add on springs in parallel (see above) to a fixed load and examine what effect this has to the extension of the springs. The load that will be kept the same throughout the experiment will also be kept at mid-point of all springs.

EXTENSION will be the increase in length compared to the original length with no force applied. The extensions will tell me what is happening to the length of the springs when there are more springs to support a fixed load.

PREDICTION

I predict that as I add on springs in parallel to a fixed load like so:

the extension of the springs will decrease.

A metal spring is made up of molecules. Between these molecules are attractive forces

like so:

When we add a load (N) to the spring the length of the spring increases, (it stretches) and therefore becomes weaker. The force pulling the spring is pulling on each molecule inside it. The force, acting on the molecules, makes them pull away from each other. When this happens the resultant force decreases and the spring extends. (Found information for last sentence in a revision text book)

When we add on more springs, in parallel (to the same load), the extension will decrease because the molecules are still being pulled apart, but not as much as before because the force exerted by the load is shared between all the springs. There is the same amount of force as before but now the same amount of force has to pull more molecules (because there are more springs) apart so less extension. Less force acts on each molecule.

In series 1 spring In parallel ‘2 springs’

If there are double the amount of springs in parallel then I predict that the extension will be half.

I predict that the extension is inversely proportional to the number of springs.

If I applied 2N to one spring and the extension was 5cm then if I added on another spring (in parallel), I would say the extension of the springs would be 2.5cm. The extension will decrease and will be half the original extension because there are now two springs to share the load. The molecules in each spring have half the amount of force acting on them now, than when there was only one spring, so they are not stretched apart that much. (By increasing the number of springs and keeping the weight constant less, force will be acting on each spring, meaning less force will be acting on each molecule).

Mathematically I would say the extension of springs in parallel is the original extension with just one spring divided by the number of springs that you are looking at. E.g. if the original extension is 20cm. Then the extension for 2 springs in parallel will be 20/2 = 10

From what I have said in my prediction, I predict that a graph for number of springs against extension will look like this.

Background Knowledge (looked up some things on Encarta)

In my experiment, I am going to be using a spring. I have found that if a material quickly regains it shape after an external force has stretched, bent or compressed it, then it will make a good spring. This is called elasticity. The external force creates stress in the material, which creates the material to deform. I have found from previous experiments that up to some maximum load (known as the limit of proportionality) the extension of a wire or spring is proportional to the applied load. This is known as Hooke’s Law. If the external force is too strong the material can become permanently deformed and Hooke’s law no longer applies.

A spring extends because the force of gravity pulls on the weight. The spring can support a weight because of the forces of attraction between the molecules in the spring. The pull in the spring, which supports the weight, is called tension. (found in a GCSE text book)

I will be using steel springs. I could use a copper spring but it is not that springy. Copper follows Hooke’s Law up to a point. When force is applied it gets easier to stretch and begins to flow until it snaps (where it does not follow Hooke’s Law).

From an experiment that I did in year nine using a steel spring I found that up to a point it extends in regular ways as equal forces are applied.

The graph I got was this.

After this point, when too much force was added the spring became permanently stretched. It did not return to its original length and when I plotted the points they looked like this.

I am going to be using a coil spring in my experiment. A steel spring is a solid and in this solid are molecules which are held together by strong forces of attraction. They are held in a regular structure like so:

The molecules vibrate to

and fro but are not free

to change positions.

I have found from a dictionary/encyclopaedia that a springy material gets its elasticity from the balance of attracting and repelling forces, which hold together the molecules.

When a spring is at rest (not squeezed or stretched) the attracting and repelling forces between the molecules are exactly balanced.

When the spring is stretched the molecules move slightly further apart. The repelling force decreases more than the attracting force. Then when you release the spring the attracting force pulls the molecules back together.

Evidence (some bits found on a DK – How Things Work CD)

The forces between molecules are electrical because within each molecule are positive and negative charges so therefore forces become attraction and repulsion. I would say that a spring is difficult ...

This is a preview of the whole essay

When a spring is at rest (not squeezed or stretched) the attracting and repelling forces between the molecules are exactly balanced.

Evidence (some bits found on a DK – How Things Work CD)

A spring is also difficult to compress because there are strong repelling forces stopping the particles getting close together.

Key Variables

Variables that could affect my experiment are

Size of spring (length & wide-ness)
Number of coils in spring
Thickness of spring
Material of spring
Load (N)

Size of spring

Springs vary in length. If I were to use different lengths of spring then I would be investigating the effect of springs at different lengths in parallel. A longer spring would extend a different length to a shorter one. It would give less extension to a shorter one. Therefore double the length of a spring would give half the extension to the shorter one to a particular weight (N). This is because the force has twice as many molecules to pull apart in a longer spring to stretch it than in the shorter one. There is double the amount of molecules in a longer spring to carry the force from the weight, so less extension.

The wide-ness of the springs will also affect the experiment. Here are two springs of different wide-ness:

A larger area of cross section gives a small extension for a particular force. Therefore double the wide-ness of a spring would give half the extension.

Number of coils

I am going to be using a coil spring. It is the most common type of spring shape. A coil spring is a spring twisted into spirals which makes it compact. It keeps the elasticity of a long spring. By having more coils, the spring becomes more compact.

Thickness of spring

I have found that a spring is a solid made from molecules that have attractive forces between them. By having a thicker spring there will be more molecules. This would mean there are more molecules for you to stretch the spring apart. Therefore by having a thicker spring there would be less extension because the force from the load would be acting on more molecules. A thicker spring is stronger so it will hold more load.

A stronger spring would have a thicker material giving a small extension. A weaker spring would have a thinner material and would give a large extension.

Material

From my knowledge I know that steel is a better elastic than copper. Copper is elastic but not as elastic as steel. As I said in my background knowledge it follows Hooke’s Law up to a point. (It gets easier to stretch as more weight is applied and begins to flow until it snaps). A steel spring is much more difficult to stretch than copper. If I were to use a steel spring and a copper spring there would be a very big difference in extension when a particular weight (N) is applied. Copper would extend more than steel when the same weight is applied to each. A copper spring will extend more because the molecules are easier to pull apart than in steel.

I am going to use all steel springs in my experiment.

Load (N)

The load is the force. When it is added to a spring, it stretches it. Buy changing the load the extension is varied.

Control Variables

Things I will keep the same are:

Ruler
String (& position)
Springs
Load(N)
Distance between springs
Dowel
Temperature (but not in our classroom)

Ruler

I must use the same ruler other wise the readings will not be fair. There could be a millimetre difference between two rulers. This would give different readings, which would be unfair and also inaccurate.

I will make sure the ruler is kept at the same position at all times. I will make sure it is standing at 90 to the stand. When I take the readings I will take them at eye level each time.

String

The string must be in parallel in with the springs. I must keep the same string and keep it in the same position because otherwise the dot that I draw (explained in method) will move and I will be given incorrect readings.

Spring

I will use the same springs for all the readings obtained, and the same type (coil) of springs throughout the whole experiment. I will make sure that all the springs that I use are all steel springs. I can’t use different materials of springs because I have decided to use all the same type of springs, in this case all steel springs. Different materials of springs will have different amounts of molecules in them.

I will make sure I use the same length, thickness and wide-ness of springs. This way I know that there are the same amounts of molecules in each spring. The weight has equal amounts of coils to pull apart.

Load (N)

On the first page of my planning I said was going to keep the load constant. So I will not change the load in my experiment. It will be the same all throughout my experiment. I am not going to change it because if I did then I will be looking at what happens to the extension of springs in parallel when different loads are applied and this is not what I have decided to do. From using what I know, I don’t think that I would find out much of a conclusion to the question if I changed both the load and number of springs.

Distance- between springs

I will keep the same distance between each spring. and the load at mid point between the springs (in parallel). This way each spring has the same chance of extension. (I predict here that by doing this the weight will be shared equally between all the springs).

Dowel

I will use the same dowel throughout the experiment. I will use the same length of dowel as well as same thickness. If I use different pieces of dowels of different weights then this would be unfair because it will effect the pull on the molecules in the springs if the dowel is very very heavy.

Temperature

Temperature will not really effect my experiment because room temperature is not hot or cold enough. If room temperature were very high then it would give more energy to the molecules in the spring, so it would stretch easily.

If room temperature were too cold then the molecules would have very little or no energy, so it would be very difficult to stretch the spring.

The variable that I will be investigating will be extension and the variable I will be changing is the number of springs.

I am going to complete the experiment in one go (one lesson) to make it a fair test. I will do this because I could get different apparatus next lesson which will effect my readings.

To make my readings more accurate I have decided to use a pointer that will be placed at the bottom of the spring.

Method

First I will get all the apparatus that I need to carry out the investigation and obtain my results.

Apparatus

8 identical steel springs –(coil spring)
2 x wooden dowel
Clamp stand & 2 boss stands
Safety glasses
Pointer (made from splint) – to red off readings accurately
Protractor- to make sure pointer is at 90
String
Scissors
Masking tape
Weight
1 meter rule

I have chosen 8N because I know that the spring is obeying Hooke’s law at this weight. It is still elastic at this weight.

I will set up my experiment like so:

*Stretching force will be kept constant throughout the experiment*

I will make sure everything is firm. I will clamp the ruler along side the spring and attach a horizontal pointer to the bottom of the spring in such a way that the pointer is close to the surface of the ruler and is at 90 to the spring.
I will then take a reading of the length of the spring with no load and mark a dot on the string. Like so:

Then I will apply 8N to the spring and record the reading, which the pointer points to on the string. I will mark a dot here and measure between the two dots. Like so

This measurement will be the extension. (This is easier than previous experiments because now I do not have to take the original length of the spring away from the reading that I get with a load and spring).

Then I will add another spring in parallel and put the load at mid-point between both springs.
I will note down the reading. (the reading will be repeated three times and averaged)
I will then add on another spring (in parallel) until there are 6 springs in parallel. Each time I add on a spring, before I add it on I will take off the load, add the spring and then add on the load at mid-point.
I will repeat the experiment three times and record the results.
So I will end up with three readings for each number of springs. I will add all three readings and divide by three to get an average result for that particular reading.

This what I mean

E.g. No. Of springs Extension (cm) Reading Average

In parallel 1 2 3

After I have got my average results, I will use them to plot a graph. I will plot a graph of extension against number of springs.

I am taking 3 readings of each extension and a range of 6 readings. I think this will give me a firm conclusion.

Readings I will take

Firstly I will take the measurement of how long the length of the spring is with no load on. Then I will take a reading for the length of the spring with a load on. I will then take readings for the extension when there are 2,3,4,5 and6 springs are in parallel. I will repeat this 3 times. When taking the readings I will make sure that I read off at eye level.

In this experiment, I will be measuring the extension of springs when more springs are applied in parallel.

Safety

When doing the experiment I will make sure that my feet are not directly or very close under the spring with the load on. This is because if the spring ‘gives’ then the load could fall on my feet and damage them. To help this not to happen I will make sure the spring is firmly clamped to the re-tort stand.
I will also make sure that I am wearing safety glasses because springs are springy and could bounce or shot into someone’s eye.
I will also follow all lab rules.

Preliminary work

I know that my method is going to work because I have done some preliminary work before.

When I did the preliminary work I set up the experiment and did exactly as I explained in my method, but this time, I used a 6N weight instead. I did this because I was testing if my method worked. In my method, I said I was going to use 8N and I still am, but this is to see if the method works well.

I obtained these results.

I have found that as the number of springs increases the extension decreases.

This is a good conclusion and therefore I think it is a good method of how to do the actual experiment. It is also a good method because I have obtained similar repeat readings. I have decided not to use a pointer as it kept getting in my way, and it was difficult to keep it at 90 at all times.

ANALYSIS

I have found from looking at my results in my result table and my graphs, that as the number of springs increase (in parallel) the length of extension decreased. After doing the experiment I plotted two graphs.

My first graph is average extension against number of springs. It shows a curve that is decreasing. There is big decrease between the first two points.

My second graph is an inversely proportional (1/Ex) graph. It has a straight line of best fit where most points fit on or are close to the line of best fit. This graph shows that the extension is inversely proportional to the number of springs, when the load is kept constant.

What I have found out, matches exactly with my predication, and confirms my understanding of the science behind it. – As more springs were applied, in parallel, to a fixed load, less force was acting on each molecule in the spring. Less force meant that the molecules were not being pull apart so much. Therefor there was less extension.

I also said in my prediction that as the number of springs are doubled the extension will halve. This did happen. Taking readings from my 1/Ex graph, when there are 2 springs in parallel the 1/Ex is 77cm, then when the number of springs are doubled to 4 springs in parallel the extension is 159cm. 77cm is about half of 156cm. There is a difference of 1cm. This concludes that my prediction was correct – when the number of springs is doubled, the extension, is halved.

The results were inversely proportional. I would say this occurred because when the number of springs were doubled, the number of molecules also doubled. When the number of molecules are doubled, they take half the amount of force acting on them than before. (when the force is kept constant)

This is what I mean by a diagram

In series 1 spring In parallel ‘2 springs’

Because I can draw a straight line through most of my results on the inverse proportional graph (1/Ex), I can say that the two variables are proportional. Mathematically this would mean that the x-axis is proportional to the y-axis – x y . As I have learnt in maths the proportional sign can be replaced to an equation - y=mx + c. m and c are constant values. C is where the line passes through the y-axis, therefor if the line passes through the origin then c is zero. This would leave y=mx. m is the gradient of the line.

These are the calculation that I did to get the gradient of my inverse proportional graph.

m = y

m = Ex2 – Ex1

S2 - S2

m = 136cm – 59cm

3.5 –1.5

m = 77

2cm

gradient = 38.5cm

Evaluation

From my experiment, my prediction was correct. The extension of the springs began to decrease as more springs were applied to a fixed load. I would say that my procedure was quite good because I can give a good conclusion, and that my results are accurate because most of my repeat readings are similar. I think my procedure was good but not excellent. I think there could have been improvements.

My table shows all the results and then the average results. By looking and doing calculations, the greatest variation of any measurement was 1.00cm at ‘2 springs’ in parallel. As I went down the table of greatest variation, the variation decreases. This, to me, is odd because as there were more springs in parallel the extension got less and I found it difficult to read off readings.

From looking at my graph, I have an anomalous result at ‘5springs’ in parallel. It does not fit the line of best curve. All the other results fit quite accurately on the line of best curve. I think I got this anomalous result because I might not have read off accurately, but then again, I obtained similar repeat readings. Another for this inaccuracy could have been that I measured inaccurately, or placed the dot in the wrong place on the piece of spring. I tried to keep my eye level with the bottom of the spring as best as possible but it was not easy. I could have received an anomalous result because the dowel may not have been exactly horizontal. I found it difficult to get the dowel balanced with an odd number of springs. There could have been a variation between the strengths of the springs. It was difficult to get exact identical spring for this experiment. Some springs could have been stretched more than others. To improve on this if I were to do this experiment again, I would make sure that all the springs are new and have not been stretched. Every time a spring is stretched, it looses its elasticity.

After doing my prelims, I decided that a pointer was not very good. The point was too thick so I left it out. The pointer, I found got in my way really when going to mark a dot on the spring. Next time I could improve by using a very sharp pointer and place it so that it does not get in my way but also does the job.

I think that my results are good enough to support a firm conclusion. I say this because most points on my graphs are either on the line of best fit or close to it.

Further investigation

The following, are several other things that I could investigate, into the effect of springs in parallel.

I could look at temperature and ask myself ‘What happens to springs when the temperature is high?’ I would say it would be easier to stretch. The extension would be more, compared to the results that I got in this experiment.

I could change the extension between the springs. I could do exactly as I did in the previous experiment but this time I would put the springs further apart from each other.

I could use different strengths of springs. Weaker springs would give a greater extension than a stronger one. This experiment, I think, would have been more reliable because I have found that results with little extension are not very accurate. This is because it is harder to measure. A millimetre each way on a small extension would have a great effect than a millimetre either way on a larger extension.

Experiment

Using the results that I obtained in this experiment and the following experiment, I could investigate further.

This time, instead of using 2cm springs I could use double the length – 4cm springs.

I predict that these would give a greater extension, and therefor the results will be more reliable (explained above). I would keep the load constant, at 8N and measure the extension. I would vary the number of springs.

I would do exactly as I did before but this time will also use a pointer (that doesn’t get in the way) and make sure all readings are read off very accurately.

This time I would use 8 springs instead of 6. This way I am looking at what happens if I add even more springs in parallel.

Method- for further investigation

Apparatus

8 Identical steel springs –(coil spring) 4cm in length
2 x wooden dowel
Clamp stand & 2 boss stands
Safety glasses
Pointer (made from splint) very sharp
String, pen, protractor
Scissors
Masking tape
Weight
1 meter rule

I will set up my experiment as I did in the planing under the heading method, but this time use longer spring (double the size)

*Stretching force will be kept constant throughout the experiment*

I will make sure everything is firm. I will clamp the ruler along side the spring and attach a horizontal pointer to the bottom of the spring in such a way that the pointer is close to the surface of the string (which will be in parallel with the string) and is at 90 to the spring.
I will then take a reading of the length of the string with no load and mark a dot on the string. Like so:

Then I will apply 8N to the spring and record the reading, which the pointer points to on the string. I will mark a dot here and measure between the two dots. This measurement will be the extension.
I will take off the load and add another spring in parallel and apply the load again, at mid point. I will read off the reading and record it.
Repeat the step above until there are 8 springs in parallel.

I will repeat the experiment three times and record the results. Each reading will be averaged.

After I have got my average results, I will use them to plot a graph. I will plot a graph of extension against number of springs.

I would then get the results from the previous experiment, and this one, and compare the results.

Results

The length of the springs that I used was 2cm. I used 8N.

Calculations for average for each number of springs

= reading 1 + reading 2 + reading 3

E.g. for ‘number of springs in parallel 6’

= 4.3cm +4.2cm+4.3cm

=4.27cm (2dp)

Calculation for greatest variation

= the biggest reading for each number of springs – the smallest reading

E.g. for ‘number of springs in parallel 2’

=reading 2 – reading 1

= 13.5cm – 12.5cm

greatest variation = 1.00cm

An Experiment To Examine the Effect of Springs In Parallel

SPRINGS IN PARALLEL

PREDICTION

This is a preview of the whole essay

ANALYSIS

Evaluation

Document Details

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