Factors that have an affect on frictional force are:
- Mass of the object
- Size
- Surface texture
- Surface area
- Applied force
- Lubrication
- Angle the object is placed on
My investigation is to find the relationship between the pulling force and frictional force of an object weighing 100g to 1000g.
Hypothesis/Prediction
I predict that as the weight of the object increases so will the frictional forces, which will also increase the pulling force, therefore making the weight of the object, frictional force and the pulling force directly proportional.
Predicted Graph
Preliminary Work
I choose my range and equipment based on what was available and what was suitable and reasonable to carry out my investigation.
A metre stick was used to ensure a constant distance and because the classroom desk restricted me from using a longer distance.
There is a 100g difference between each weight tested which should be sufficient enough to show the affect of weight vs. frictional force. I also wanted to use a solid number instead of a number like 120 for example. 20g is too little of a difference to show the affect of weight vs. frictional force. Also a difference of a large number like 1000g would have been too large to notice the difference.
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100g → Wooden block
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200g → Wooden block + 1 x 100g weight
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300g → Wooden block + 2 x 100g weight
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400g → Wooden block + 3 x 100g weight
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500g → Wooden block + 4 x 100g weight
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600g → Wooden block + 5 x 100g weight
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700g → Wooden block + 6 x 100g weight
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800g → Wooden block + 7 x 100g weight
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900g → Wooden block + 8 x 100g weight
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1000g → Wooden block + 9 x 100g weight
Equipment
Methodology
- Set up as shown above.
- The pulling force will be applied by weights hooked onto the end of the string.
- Weights ranging from the weight of 5g, 10g, 20g, 50g, and 100g were used to get the most accurate results.
- Place ruler is a suitable location so it doesn’t get in the way and in on the classroom table completely.
- Set up the right mass of the object placing 100g weights to increase the mass.
- Make sure the string is securely attached to the wooden block and place on the wheel of the pulley. Also make sure there is a hoop at the end so the pulling weights will be able to pull on the string.
- add weight to apply pulling force
- start off with a low number anything less then the mass of the object then steadily increase it until the wooden block/wooden block + weights starts to move at a steady slow speed for the length of 1 metre.
- Repeat 3 time to get a range for the pulling force need to make the wooden block/ wooden block + weights at a constant steady slow speed.
Fair Test
To make my investigation a fair one I have taken several procedures to ensure fair and accurate results.
- The same part of the classroom table was used in each test. Varying the area can alter the results because each bit of surface is different. Some differences are visible and most of the differences aren’t. Microscopically the table surface is rough.
- The same wooden block was use for all tests. Just like the table the wooden blocks’ surfaces vary and using different blocks will alter results.
- The same pulley was use since the pulley has a more constant pull then me pulling by hand with could vary in speed. Each pulley turn differently some are stiff and some are too lose so using the same pulley is very important.
- Each test was done three times to check the accuracy of each result
- A metre stick was use to measure the distance the block traveled. A metre stick helped to ensure a constant distance for all trials.
Results/Observation
I increased the masses by 100g and found the following results, which I repeated and averaged.
As the weight of the object increased so did the pulling force. Since the frictional force got stronger as the weight of the object increased the pulling force required to pull the object also had to increase.
Analysis/ Conclusion
In my plan I stated that friction is dependent on the amount of force that the objects are pressed together with and that the increase in weight would be directly proportional to the frictional force. This is because the increase in force causes the atoms of the surfaces to press closer together. Microscopically the surfaces of the tabletop and the wooden object aren’t smooth even though they may appear. The surfaces are actually filled with, hills, valleys, projections and ridges hundreds or even thousands of atoms deep. Only a small fraction of the surface atoms are touching to cause an attraction.
Looking at my graph of the comparison of trials the pulling force needed is in the pattern of a directly proportional graph.
In Conclusion, as I predicted the pulling force increased as the mass of the object (wooden block/ wooden block + weights) increased making then directly proportional within the range I tested and may go wrong if the wooden block used is deformed and rough. However, my results strongly support my prediction.
Evaluation
The procedure went very well. The readings I took were as accurate as I could make them. The smallest weight that I used for pulling force was a 5g weight. I didn’t have any anomalies; all of my trials are precise and reliable.
Overall, my results strongly support my conclusion there were no obvious mistake but possible human error. If I was to do this investigation again I would calculate a steady speed so instead of judging what I thought was a steady speed.
Reference
-
By John E. Betts Physics for Technology 2nd Edition 1981
Reston Publishing Company,
A Prentice Hal Company
Reston, Virginia 22090
- By Martin Harrison and Frank McKim Mastering Physics 1990
Macmillan Maker Series 4th Edition
Macmillan Press Ltd
Houndmill Basingstoke
Hampshire RG21 6XS
London
- Stephen Pople Explaining Physics GCSE Edition 1990
Oxford University Press,
Walton Street
Oxford
OX2 6 DD