I drew a line of best fit when I had plotted my findings and discovered that the results should be in a straight line and when I draw the line of best fit it should go through the origin of (0,0) the reason being that this was not the case was because, the springs where in a state of compression and therefore would not have followed Hooke’s law to start with. This told me that when I do my focal experiment I would have to put a mass of 100g on and count this as 0g, as after 100g the spring follows Hooke’s law according to the results of the preliminary experiment. The graphs also led me into thinking which spring I should use on the main experiment. The type of spring that I will be using in my investigation is the short spring because, when I examined my graphs and compared the results of the short spring against the long spring, I found out that the gap between the extensions on the long spring was larger than the gap for the short spring. In using the smaller length spring I am minimising the chance of error when I calculate the length of the spring. Also as part of my preliminary work I learnt that there was other things that affected the extension of a spring these were;
- Material of the spring
- Downward force applied to spring
- Length of the spring
- Number of coils in the spring.
- Diameter of the spring material.
In terms of molecules the material of the spring affects the extension because, different types of material have different intermolecular forces between them and in some materials the force is greater than that in others and consequently this means that the spring doesn’t extend as much as one with a weaker intermolecular force. Also the downward force applied to a spring effects the extension; a greater mass will extend the spring further than a mass that is lesser. Which means that if I use different masses each time I carry out the main experiment then it shouldn’t follow the trend of Hooke’s law exactly for example, if I start off with 50 grams then add 25 grams then 100 grams then another 50 grams after that when I plot the graph the coordinates will be all over the place, therefore I will have to increase the mass on the spring in equal increments, e.g. 50 grams the another 50 grams e.t.c. The more number of coils affects the length of a spring because. The diameter of the material affects the extension of the spring opposed to a different spring with a different diameter because. Therefore I predict that the greater amount of force that I apply to the springs the greater that the spring will stretch. I think that if I was to start off with a spring that was 100mm in length and I added 50g then the length of the spring will now be 125mm. The extension of this is 25mm. Therefore if I carried on with this I predict that if I plot a graph showing extension against the amount of masses added then it will look something like this;
Method
Equipment
The equipment that I will need for this practical part of the investigation is;
- Clamp stand
- Meter ruler
- Short spring
- Goggles
- Masses (50g)
- Pen
- Paper
Safety Issues
I will have to consider safety issues whilst carrying out my investigation for obvious reasons. I will have to wear goggles to ensure that, if I take the spring that I am investigating past its elastic limit that it will not flick up and strike my eye. Safety in the actual lab has to be considered, all stools have to be tucked in under the desk and coats and bags need to be hung up neatly at the side of the classroom away from any investigations. Also I will have to be alert to respond to any instructions that the teacher has to put forward and the practical work it self has to be taken seriously and maturely.
Fair Test
I will have to keep this investigation a fair test do that my results are as accurate as they can be. The way that I will keep it a fair test is that I will only have one variable and I will have to accurately measure the length of extension and not just round it to the nearest decimal place. Also I will go up in equal increments so that when I work out extension according to Hooke’s law the extension should be equal more or less throughout the investigation. I will also be repeating my investigation because by having to sets of results I wish to find an average to increase the reliability of the results. I will also take the length of the spring before the investigation is carried out so that I have something to go on and find an extension from at the start, also I will use the same spring and not change the spring half way between the investigations to ensure that results obtained are precise. Another factor that I will be keeping a close eye on is the motion of the spring I will make sure that the spring is not bouncing up and down when I measure it or rocking from side to side.
How will the Length of the spring be measured at each Stage?
The way that I will be measuring the length of the spring at each stage is called a ‘loading and unloading’ method. The advantage of using this method of investigation is because each time you put on a weight you extend the length of the spring, by unloading the mass once it has been put on the spring then applying the greater mass afterwards you are able to check that the spring has not been taken past its elastic limit and that it resumes back to its original position. This is an enhanced way to investigate Hooke’s law rather than just keep adding the masses at each stage.
I plan to record my findings in a table like the one below;
When I have worked out an average I will put my average results into a table like the one below;
The way that I will find out the extension of the spring is using the formula below;
Extension = New length - Original length
The way that I will find out an average from my results is to use the formula below;
Average = Results ÷ Total number of entries
Independent variable: Weight Applied
Dependant variable: Extension
Step by Step Method
- Gather equipment needed and put on safety goggles.
- Set up the clamp stand with the spring suspended from the clamp stand
- Apply the 100g of weight to overcome the compression and leave this
- Measure the spring and take this measurement as its original length to work out extension from later
- Apply the first weight which will be a increment of 50g
- Using the meter ruler carefully and accurately measure the length of the spring now
- Record the length of the spring using the pen and paper
- Take off the 50g and let the spring resume its original position to make sure that it has not gone past its elastic limit
- Add on the next set of increments (Which will now be 100g)
- Take the length of the spring now
- Record the length of the spring
- Take off the masses
- Repeat steps 9 and onwards making sure that you are increasing the increments until you reach 500g.
Results
Working out Average Extension;
50g = 25 + 25
= 50 ÷ 2 = 25
100g = 50 + 55
= 105 ÷ 2 = 52.5
150g = 70 + 65
= 135 ÷ 2 = 67.5
200g = 95 + 91
=186 ÷ 2 = 93
250g = 120 + 113
= 233 ÷ 2 = 116.5
300g = 140 + 145
= 285 ÷ 2 = 142.5
350g = 165 + 165
= 330 ÷ 2 = 165
400g = 180 + 180
= 360 ÷ 2 = 180
450g = 200 + 205
= 405 ÷ 2 = 202.5
500g = 225 + 230
= 455 ÷ 2 = 227.5
I will now put what I have worked out in a table then plot a graph of the mass against the length of the spring and another graph showing the mass against the extension.
Conclusion
By looking at my graphs I can see a trend. On both graphs series 1 represents the first investigation into Hooke’s law and series 2 represents the second investigation that was carried out for reliability.
Evaluation