In this experiment I will be intending on observing how the change in the force of the weights affects the depression of the ruler. I will observe if the depression will increase as we increase the force of the weight. I will be measuring the changes in the depression using a 1m ruler which will give results in cm. I will be investigating if my results agree with Hooke’s law.
HOOKE’S LAW
This physics experiment is based mainly on Hooke’s law. In the textbook Physics for AQA by Patrick Fullick it says “Robert Hooke mainly came up with the idea that materials like metals stretch in proportion to the force applied to them until their elastic limit.” This basically meant that as a wire begins to stretch the atoms in that metal move apart in a regular way so that the extension of the wire doubles each time that the force doubles. As the wire continues to stretch, the atoms in the metal move even further apart. As soon as the elastic limit is reached, the layers of the atoms slide over one another, and the length of the wire increases rapidly. Once the force is removed from the wire, the wire does not return to its original position.
After studying Hooke’s I have basically found that the extension depends on the force forced on the object. The extension is the dependant and the force is the independent. This is described in the book Physics for AQA by Patrick Fullick as “the fact that materials like metals stretch in proportion to the force applied to them up until to their elastic limit”. Here are a few examples of dependant and independent objects:
This piece of scientific knowledge on Hooke’s law supports my plan which I have decided to use in this physics experiment. In my plan I am going to increase the force of the weight stage by stage. I will be observing if the ruler reaches its elastic limit and whether the ruler comes back to its original position. I will also be observing if the extension of the object does depend on the force of the material.
From this scientific knowledge I have also come to a prediction that as the force of the weight increases, the angle and depression of the ruler will also increase. Proving that the extension of the ruler does depend on the force of the weight. I will also expect the ruler to increase in length and be slightly out of shape after reaching its elastic limit.
We also carried out a preliminary experiment before the actual experiment. By doing this preliminary experiment we could achieve accurate and useful results in the near future. This experiment helped us decide how many times we should repeat the experiment to achieve accurate results. It also helped us decide where we should place the string on the ruler to get efficient results. The preliminary experiment also helped us make a decision on where how far off the table we should place our ruler to get efficient. The preliminary experiment also helped us decided whether we should have also changed the position of the weight and not just the force of the weight.
A RESULTS TABLE FOR THE CHANGES IN DEPRESSION WHEN THE FORCE OF THE WIEGHT IS CHANGED.
All the results I gained were correct to 2 decimal places. All of my results were recorded using a 1m ruler, I used the cm on the ruler. To ensure that my results were as accurate as possible I repeated the experiment three times and then gained an average.
ANALYSIS
From my results I have found that as we increase the force of the weight, the depression of the weight and the angle of the weight increases. I have noticed that as the force of the weight increases by 100g the depression of the ruler increases by 0.40 to 0.30cm each time.
CONCLUSION
From this investigation I have found that as I increased the force of the weight the depression of the ruler from the normal increased. This resulted in proving Hooke’s law that the extension of the object does depend on the material. As I consistently increased the force of the weight, the angle of depression gradually also increased, resulting in the ruler increasing in length. This is because as the ruler begins to stretch the atoms in that ruler move apart in a regular way so that the extension of the wire doubles each time that the force doubles. As the force of the weight increased the ruler will continuo to stretch resulting in the atoms moving even further. Eventually the ruler will reach its elastic limit and the layers of atoms side over each other resulting in a rapid increase of length. Once the ruler was out of length the ruler could not return to its original position, so as I kept on increasing the force of the weight the ruler might have given me inaccurate results.
From my graph (next page) I have found a reasonable pattern which supports my prediction and Hooke’s law. It appears the line of best fit (which is a straight line) rising diagonally to the right as the depression of ruler from normal increases (x axis) and the weight on ruler increases (y axis). This graph points out that extension of the ruler depends upon the force of the weights.
My conclusion does support my previous prediction that as I increase the force of the weight the depression of the ruler from the normal increases. As I kept increasing the force of the weight by a 100g, the depression of the ruler increased by 0.40 to 0.30cm. My conclusion also supported my other prediction about Hooke’s law proving that the extension of the ruler depends upon the force applied. My conclusion also supports my prediction that the length of the ruler will increase slightly because of Hooke’s law, providing me with slightly inaccurate results.
EVALUATION
I think my investigation went pretty well. I am very pleased with the results I gained because they had shown me a good trend/pattern which I could refer to.
My graphs showed me a good set of results which I really expected. My graph had a straight line of best fit which represented the results gained. The graph had a straight line travelling diagonally upwards towards the right which I pretty much expected, because as the force of the weight increased the depression of the ruler also increased which meant that the straight line would travel diagonally upwards and towards the right. There was one or two anomalous gained from my graph, this might have been because of the human errors and unavoidable certainties due to parallax error.
I think the procedure I used was quite suitable for this experiment. I varied the force of the weight greatly from 100g to 1000g which gave me reasonable results which I could come to a conclusion with. For each different force I repeated the procedure three times and then I achieved an average which would give me more accurate results. The apparatus I used for this experiment also made sure that I gained accurate results, to measure the depression of the ruler I used another ruler which had been vertically secured which gave me measurements in cm. The ruler I used that had the weights hanged on also had measurements which let us know where the piece of string should remain throughout the whole experiment. If we had used a normal piece of wood the piece of string might have slightly moved position all the time which could have affected my results. I also used a block of wood to secure the parallel ruler to the table which would stop the ruler moving about and giving me inaccurate results. I secured the block of wood to the ruler using a G-clamp. By using this equipment my accuracy improved greatly.
I could have improved my procedure for this experiment by using more accurate equipment such as right angle triangle rulers. I could have also varied the force of the weight bit more to see if the ruler reached a point where it would stop depressing and stay the same position. I could have repeated the procedure more times for each different force on the weight to achieve improved results.
I think my results were quite reliable. There were a quite a few problems which affected my results. The fact that we couldn’t stop the weights hanging on the piece of string swaying side to side hindered our results. The main problem was Hooke’s law. As the force of the weights increased the ruler begins to stretch the atoms in that wood move apart in a regular way so that the extension of the ruler doubles each time that the force doubles. As the wire continues to stretch, the atoms in the wood move even further apart. As soon as the elastic limit is reached, the layers of the atoms slide over one another, and the length of the ruler increases rapidly. Once the force is removed from the wire, the wire does not return to its original position. This affected my results somewhat badly. Another major factor which could have affected my experiment badly was parallax error. Things such as human errors by members of the group could have also affected the standard of my results.
I think the results I gained from this experiment were sufficient enough for me to come to a formal conclusion. I predicted before the experiment that as the force of the weight increased, the depression of the ruler from the normal would have also increased. This would prove that the extension of the ruler would really depend upon the force of the weight. I also made the prediction that the length of the ruler would increase and it would be slightly out of shape due to Hooke’s law. The prediction I made agreed with the Hooke’s law and my results from this experiment.
There were a number of anomalous results in my investigation. This might have occurred because:-
- Human error with the measurements.
- Beam quicker before we started.
I could have carried out some further work on this investigation to extend and broaden my results. I could have investigated different things such as rulers with different thickness, different material, I could have also changed the length of the overhead. I could have investigated how much weight would I have to put on to the ruler until it reached its elastic limit. I could have done another experiment using varying the same amount of weights and using the same objects but this time changing the position of the weight and linking them together. I could investigate if the results agree with my prediction and Hooke’s law.
