My method is to connect the spring to the clamp, attach the mass to the bottom of the spring and measure it by holding a ruler to the side of it. Then I will calculate the extension of the spring by subtracting the stretched length of the spring from the original length of the spring.
Results:
I varied the mass instead of the weight because 100g = 0.98N, it would have been awkward to measure in weight because the numbers would not have been whole, this would have made calculations more difficult so it was more convenient to measure in mass.
I did not measure the reading exactly, instead I measured it approximately to every 5mm because I just wanted a rough idea of what was happening.
I noticed that the extension of the spring increased as I added more mass and there was an extension of approximately 40mm between each reading, this means the spring was stretching by the same amount each time a mass was added. My graph shows a line of best fit that is straight. This means that the load and the extension are directly proportional. Anomalous results in my preliminary could be because I did not measure the reading on the ruler exactly; instead I measured it approximately to every 5mm. I did not measure accurately because I just wanted a rough idea of what would happen.
Prediction
My prediction is that the greater the force the greater the extension of the spring. I predict this because my preliminary showed me that as I increase the load, the extension of the spring increases and my background knowledge tells me that Hooke’s Law states that the extension of the spring is directly proportional to the load exerted on the spring, so if I double the force the extension will double, if I triple the force the extension will triple etc. I think this will happen because the force of gravity is pulling the bottom of the spring further down.
Apparatus
The apparatus I will be using is:
- Two clamps (one to suspend the spring from and the other to hold the ruler)
- A ruler to measure the length of the spring
- A spring
- A pin sized pointer to measure the readings on the ruler more accurately
- Masking tape to attach the pin sized pointer to the spring
- 1N weights
Fair Test (Variables and Constants)
I will make it a fair test by using the same apparatus throughout my experiment apart from the one variable I am changing which is the weight. I will vary the weight by increasing it by 1N each time. The variables that shall remain constant are the ruler, spring, clamps and pin-sized pointer. My input variable is the one I am exploring which is the weight. My output variable is the extension of the spring.
Range
I do not know the range of values I shall use because I will begin by using 0N and increase this by 1N each time until the spring is permanently deformed.
Method
The main steps for setting up the apparatus are:
- Hang the spring from one of the clamps
- Using the making tape attach the pin sized pointer to the loop at the bottom of the spring
- Connect the ruler to the other clamp making sure the pin sized pointer is in line with the number ‘0’ on the ruler
- Measure the original length of the spring
- Gently place the weight in the loop at the bottom of the spring
- Wait until the spring has stopped moving
- Using the pin sized pointer and the ruler measure the length of the spring
- Make a record of the results
- Calculate the extension of the spring by subtracting the stretched length of the spring from the original length of the spring
- Repeat the experiment for the same weight to obtain a more accurate result
- Repeat the experiment again, but this time increasing the weight by 1N
Diagram:
Safety
Safety precautions were taken to reduce the risks of accidents occurring. To make sure my experiment was safe someone in my group held down the clamp, to prevent it from falling over and hurting anyone.
Observations
When the weights were put on I noticed the coils on the spring were separating. The more weight I exerted on the spring, the more the coils separated and the longer the extension of the spring. When the weights were removed, the spring returned to its original shape. When I put on 12.74N, I noticed the coils at the end of the spring separated and began to unravel, until the coils finally straightened out and the spring fell off the clamp. The experiment was repeated if a reading seemed inaccurate or if something went wrong, for example the experiment was repeated when the pin sized pointer was tilting too much and I could not see the reading.
Results:
Relationship and Explanation
The line of best fit in my graph is at first a straight line; this shows that the relationship between the force and extension is directly proportional. The spring obeys Hooke’s Law, which states that the extension of a spring is directly proportional to the force applied. My graph shows that when there is no weight on the spring there is no extension, this is because there is no force acting on it so there is no change in shape. Then when more weights were added the spring stretched by a similar amount each time. Here the stress (the force exerted on the spring) is small enough for the spring to retain its original shape but when 12.74N was added the spring extended a significant amount, here the spring reached its elastic limit (the point where the graph is no longer straight) and could not withstand the stress, its molecular structure was changed leaving it permanently deformed. When this happens the bonds between the atoms are broken and the space between the atoms is increased, after this the atoms do not regain their original positions and the spring no longer obeys Hooke’s Law.
Comparison with Prediction and Conclusion
My findings support my original prediction, which was the greater the force the greater the extension of the spring. This was because my I knew the spring obeyed Hooke’s Law from my background knowledge.
Anomalies
Anomalous results in my experiment could be due to the first weight that I measured also included the weight of the hook, so my measurement was slightly heavier than it was supposed to be. When I was trying to measure the one of the readings, the clamp was attached to that part of the ruler so I could not see the reading properly. Anomalous results could also be due to human error; I may have read the wrong reading off the ruler.
Accuracy
I think my results are quite accurate and allow firm conclusions to be made. Most of my results are close to the line of best fit. However the apparatus I used was not very accurate; the ruler I used was worn out at the ends so it did not measure exactly from 0, the pin sized pointer kept tilting so sometimes it was not pointing on the correct reading.
Reliability of the Evidence
I think my results are quite reliable, if the experiment was repeated the same results would be obtained. I repeated my experiment twice to obtain a more accurate result and both sets of results are similar.
Suitability of the Procedure
Repeating my experiment over again and using better apparatus would help me obtain more accurate results. My experiment could also be made to be even more accurate by using different apparatus such as an ultra sonic measuring device.
Further Work
To find out more about how force affects the extension of a spring I could investigate springs in series and in parallel. This is where springs are combined to share a load.
