I believe that the deflection will be directly proportional to the weight being added onto it.
This investigation appears to test the understanding of moments. The equation for moments is: moment = force x perpendicular distance to fulcrum.
If the distance will be kept constant, then I can rewrite the equation into:
Moment = force x X, where moment =1, force = 1 and X is constant.
If the force were to be doubled, then force = 2, thus on the right side of the equation, force multiplied by distance gives 2X, so moment must equal 2X too.
Sources of information, including results of preliminary trials:
I conducted some preliminary trials, where I used a 1cm thick dowel. I found that the deflection was too small to measure accurately, so a decision to use a thinner dowel was made.
The equation for moment was cited from Tom Duncan’s GCSE Physics book 3rd edition.
Obtaining Evidence
Procedure:
I did the experiment exactly how I planned out earlier, with the exception of adding some double-sided adhesive tape to the rod so the weight would not slip down the rod whilst reading the amount of deflection.
Safety measures:
I made sure that all unused weights were placed away from the table edge so they would not fall onto my foot. I also made sure that no more than 500g was put onto the rod in case it were to snap and a splinter were to come into my eye.
Results:
Analysis and Conclusion
Conclusion (eg relationship between variables as given by graph)
I have to come the conclusion that the more weight added to the dowel, the more it will deflect. Looking at the graph, it appears that the relationship between the two variables is linearly proportional, seeing as the line of best fit does not pass through the origin.
Scientific explanation of results (including comparison with prediction, where appropriate):
In the planning stage, I predicted that the relationship between the two variables would be directly proportional, but given that the conclusion that the relationship is linearly proportional, it shows that my prediction was wrong.
If you consider the dowel to be like a spring, it is easier to see why the results are proportional. If the top half of the length of the dowel is under tension when being bent, and the bottom half is under compression, like Hooke’s Law, a spring will extend or shorten if pressure is applied. In this case, the things that are being extended and shortened are the molecules of wood within the dowel, so they will change size directly proportionally until a certain point, rather like the elastic limit of a spring when it will start to stretch/compress out of proportion.
The above law however, should be obeyed by the results. At a closer inspection of the graph, the results are very nearly directly proportional. Knowing that no experiment can be perfect, and there will be slight flaws, I can fairly confidently say that I was correct with my prediction after all and that the conclusion that I came up with is wrong too.
The conclusion should state that the amount a dowel bends is directly proportional (not linearly proportional) to the amount of weight added onto it.
Evaluating Evidence
In what way was the method used good/bad? Was the procedure suitable?
This method was good because it was simple to set up and easily repeatable. The measurements were also quite easy to read. The experiment was bad, however, because when no weight was added to the dowel, it bent under its own weight, thus making my graph not pass through the origin, which, in theory, it should do
Reliability of Evidence – are the results good enough to support a conclusion?
I believe that the results are easily good enough to support a conclusion because if you look at the graph in the obtaining evidence stage, the points all lie very close to the line of best fit – thus showing a very strong correlation, enough to support my conclusion.
Improvements and Complementary work:
Believe that the experiment could be improved by a few ways:
- Use a dowel which wouldn’t sag under its own weight
- Attach a drawing pin onto the end of the dowel, thus making readings a lot easier and more accurate
In addition, because the rule may have been inaccurate, I could use rules manufactured by several different companies, and measure using those, then taking another average to make sure that a fair experiment would be conducted.
