When force P continues to increase a stage will be reached when the block begins to move. At this point, the friction brought into play has reached its maximum value for the two surfaced concerned, and this is called the static friction.
I predict that the greater the weight on the wood the larger the friction therefore a greater weight will be needed to pull it off. I predict this because of previous, similar experiments and preliminary experiments. These results showed me that the heavier the object the greater the force is required to pull it. Also Newton’s law of universal gravitation states that any two particles of matter attract one another with a force which is proportional to the product of their masses… In other words the greater the weight of an object the more the object is attracted to the other. In my experiment this corresponds to the weight of the block, as it increases the attraction to the desk becomes greater therefore making the block more difficult to move.
Results:
When collecting these results I attempted to be precise as possible. I took three sets of results and averaged them, this is to try and reduce anomalous results and make the others more accurate. I took six readings so I could produce an accurate graph.
While obtaining my results I came across a number of problems which could effect the results. Firstly I noticed a number of problems with the pulley. The pulley must have its own friction e.g. where it rotates. Also during the experiment I noticed that the string was not only on the pulley but rubbing the edge of the table as it left the pulley. Secondly, I noticed that the table was unsteady, therefore it was difficult to tell if the table was flat. Having the table at an angle would effect the friction also. I also considered that where the weights were placed on the wood would effect the friction. Finally, the tables texture is not consistent e.g. engravings. Some sections were smoother and some rougher, therefore where the wood was placed for each reading also would effect the friction.
My results show a correlation between the weight added to the block of wood and the friction of the wood and the table (and subsequently the weight it takes to move the wood). From my graph you can see that the correlation is positive and fairly strong. From the averages there are no major anomalous results however all the results do not lie on the line of best fit therefore showing the results are not perfect.
In my prediction I stated that I believed that as the weight on the block of wood increased so would the friction (and subsequently the weight it took to move the wood). My results show that my prediction was correct. I know, as I aforementioned, that this is due to Newton’s Law of Universal Gravitation.
Therefore from my results I am able to conclude that the greater the weight of an object the greater it’s static friction will become. This conclusion supports my prediction fully.
If I were to repeat this investigation I would change a number of things. Firstly, I would attempt to measure the amount of friction that the pulley was exhorting. I could do this with a Newton meter. I would then subtract this friction from the final amount.
The weight applied to the block of wood was increased by 200g every time, if I had used smaller amounts e.g. 1g, then the margin of error in my results would have decreased.
Another problem with the weights was as we were adding them to the string we were adding 100g, 50g and 10g weights, therefore the margin of error here also could have been brought down by using 1g weights.
In an ideal situation the experiment would have been undertaken on a completely horizontal surface, however we were unable to make sure of this because we were not in an Ideal scientific laboratory. Another factor on the friction was the surface of the table and the block of wood. The surface of the table was unpredictable and some parts were rough and others smooth. Also the grain of the wood on both the table and the block of wood would effect the friction. This again was due to the lack of resources available to us. In an ideal situation the experiment would have taken place with a completely smooth block and possibly on glass or something extremely smooth. However if I were to repeat the experiment in the same conditions I would mark on the table where to place the wood each time I took readings, as to make it more fair.
As I was placing the weights on the wood I considered if where I was placing these would have an impact on the friction. I later found that this would due to further experiments and research. Therefore to keep my experiment fair, I would mark a point on the wood where the weights should lie during every experiment.
There were other small factors I noticed which could have changed the results, for example, the angle at which the string was coming off the wood.
Although there were a great deal of things I could have improved with the experiment I believe it was accurate and precise enough to support my conclusion. I think this because there were no major anomalies, which suggests that because of the consistency of the results they were accurate.
I would find it interesting to further investigate static friction, by increasing the angle of the table. I think this would be interesting because by increasing the angle of the table gravity has a much more influential role to play. Gravity would become a bigger factor in the experiment.
Bibliography:
Ordinary Level Physics- A.F.Abbott.
