FRICTION INVESTIGATION
PLANNING
Aim:
To investigate the effect of changing a trainer's weight on the friction that occurs when it is dragged along at a constant speed.
Possible Factors:
> Material of trainer sole
> Speed of trainer
> Forward force
> Roughness of ground surface
> Conditions (temperature etc.)
> Whether surface is lubricated
Scientific Knowledge:
Friction is a force that resists the sliding or rolling of one solid object over another.
Friction is essential, an example is the traction needed to walk without slipping, but it can also be a force that is extremely un-useful, and it can present a great measure of opposition to motion. For example, about 20 percent of the engine power of car engines is used to overcome the friction forces of the moving parts.
The major cause of friction between two surfaces is the forces of attraction, known as adhesion, between the contact regions of the surfaces, which are always irregular (albeit sometimes microscopically). Friction is caused by shearing these "welded" junctions and from the action of the irregularities of the harder surface across the softer surface.
There are things that will affect the amount of friction that occurs. One of them is the weight that presses the two surfaces together, and that friction is proportional to this load or weight that presses the surfaces together. For example, if a pile of three bricks is pulled along a table, the friction is three times greater than if one brick is pulled. Therefore, the ratio of friction F to load L is a constant one. This constant ratio is called the coefficient of friction and is usually symbolized by the Greek letter mu. Mathematically, mu= F/L. Because both friction and load are measured in units of force (such as pounds or newtons), the coefficient of friction is dimensionless. The value of the coefficient of friction for a case of one or more bricks sliding on a clean wooden table is about 0.5, which implies that a force equal to half the weight of the bricks is required just to overcome friction in keeping the bricks moving along at a constant speed. The force of friction, and the surface are of two objects, are almost entirely independent of each other, for example, if a brick is pulled along a wooden table, it will produce the same amount of friction whether it is laid down along the longest side, or positioned on one of the ends. The frictional force itself is directed oppositely to the motion of the object. This particular friction type is called kinetic friction, because it relies on two surfaces moving.
Therefore, as the type of friction that I intend to investigate is kinetic friction, if I increase the weight of the trainer, then the friction that occurs will increase, because as I have said, the weight pushing the two surfaces together is directly proportional to the friction that occurs. And also, the roughness of the surfaces will affect friction, because if the surfaces are rougher, then the imperfections will be greater in size, and so the "welded" junctions that will occur when these imperfections join together will require more force to undo, and vice-versa for a smoother surface.
There are many other types of friction, rolling, static and sliding are examples of them.
Prediction:
I predict that as the weight of the trainer increases, so will the amount of friction that occurs when it is dragged along a surface at a constant speed. I also predict that the amount of friction that occurs will be directly proportional to the weight of the trainer, and as the weight of the trainer doubles, so will the amount of friction acting upon it.
Variables:
Equipment:
* Newton meter
* Masses
* Size 10 trainer
* Ruler
* Stop clock
* Wooden desk
.
Procedure:
) First I will need to collect all the equipment.
2) Then, I will mark a 1 metre 'course' onto the wooden desk, using the long ruler. I am going to do this, so that I can keep the speed of the trainer the same throughout each experiment, this is essential for a fair test.
3) I then need to weigh the trainer, without ...
This is a preview of the whole essay
Variables:
Equipment:
* Newton meter
* Masses
* Size 10 trainer
* Ruler
* Stop clock
* Wooden desk
.
Procedure:
) First I will need to collect all the equipment.
2) Then, I will mark a 1 metre 'course' onto the wooden desk, using the long ruler. I am going to do this, so that I can keep the speed of the trainer the same throughout each experiment, this is essential for a fair test.
3) I then need to weigh the trainer, without any added weight, and record this weight in Newtons.
4) Next, I will pull the trainer along using the Newton meter, making sure to take 2 seconds to cover the 1 metre strip, I will need to do this over 2 seconds, to maintain the same speed of the trainer in each experiment, this is important for a fair test.
5) I will then repeat this a further 2 times, in order to have 3 results, and then the average of these 3 results will provide a more accurate figure.
6) Once I have completed that, I will repeat the whole experiment, increasing the weight in the trainer in 100g steps, until a there is a weight of 1000g added to the trainer.
Measurement Range:
* Trainer
* Trainer + 100g
* Trainer + 200g
* Trainer + 300g
* Trainer + 400g
* Trainer + 500g
* Trainer + 600g
* Trainer + 700g
* Trainer + 800g
* Trainer + 900g
* Trainer + 1000g
Preliminary Work:
To assist me with choosing some of my controlled variables, I attempted the experiment a number of times before the final planning of it.
After this preliminary work, I decided to use a speed of 0.5m/s, as when slower speeds were tested, the trainer's movement became erratic, and it was difficult to get an accurate reading. When faster speeds were tried, the difficulty to attain an accurate reading increased dramatically, as the experiment was over too quickly. I also decided to use a 'course' length of 1 metre because below one metre the course was felt to be too short, and therefore could have caused inaccurate results, and a length longer than 1 metre caused an uneven speed, because it was not possible to keep the trainer moving smoothly for a longer length, as when I pulled it along, I myself had to move to cover the whole course. Also, it was difficult to measure accurately above 1 metre, as this was the length of the longest ruler we could use. The decision to use a size 10 trainer came about as this was the easiest trainer size to get hold of.
OBTAINING
Safety:
There are no obvious safety hazards involved or associated with this experiment, therefore this experiment can be classed as safe. There are no dangerous substances involved, and therefore safety goggles or other protective clothing are not required.
A possible safety hazard, however, are the masses, which could fall onto a foot, for example, causing possible injury. Therefore when I did the experiment, I was careful not to let the masses get into a position where they could fall off the surface. And when carrying them, I was careful not to let them fall.
Also, when I was moving about during the course of the experiment, I was careful not to fall over anything, and therefore was careful to remove any items that I could fall over, such as chairs and bags. And I was also careful to not present myself as a danger to anybody else in the lab.
Table of Results:
ANALYSING
Trends and Patterns
From the graph, I can see there is a straight-line relationship between the trainer's weight and the force of the friction it produces. Therefore showing that the two variables are directly proportional to one another.
Conclusions
As you double the weight of the trainer, there is also an approximate doubling in the force of the friction that occurs when the trainer is dragged along at a constant speed. This shows that there is a proportional relationship between weight and friction.
These two variables are therefore directly proportional to one another.
Relating Conclusions to Scientific Knowledge
The weight of the trainer and the friction that it produces when dragged along at a constant speed are proportionally related because if the weight of the trainer is doubled, then the force with which the two surfaces are pushed together is also doubled, and so therefore double the force is needed to overcome the minute 'ridges' on the two surfaces which cause friction in the first place. Therefore the force needed for the trainer to maintain a constant speed will be doubled.
Original predictions:
My original prediction, I predicted that: "As the weight of the trainer increases, so will the amount of friction that occurs when it is dragged along a surface at a constant speed. I also predict that the amount of friction that occurs will be directly proportional to the weight of the trainer, and as the weight of the trainer doubles, so will the amount of friction acting upon it."
On the basis of my results, I am satisfied that my prediction has been proven.
In my table of results, you can see that the first, second and third attempt for a trainer weight of 5N gave results of 6.0N, 6.2N and 5.9N respectively. Thus giving me an average of 6.0N. Now, if you look at my results for a trainer weight of 10N, it can be seen that the readings for my first, second and third attempt are 12.5N, 12.2N and 12.3N respectively. This gives an average of 12.3N, which is an approximate doubling of the result for a weight of 5N, therefore proving my prediction that if the weight of the trainer is doubled, then the force of the friction produce will also double. My graph also proves that my prediction is correct, because it has a straight line with a steady gradient.
EVALUATING
Accuracy of Procedure: I believe that my procedure was as accurate as I could make it. There were no obvious anomalies, as all of my results fall very close to the line of best fit on my graph, and this line was very easy to draw.
Reliability of Results: By looking at the data in my table and graph, I can say that my results are trustworthy, and therefore they are reliable.
I feel that my results are very consistent, for example, my results for the trainer weight of 5N are 6.0N, 6.2N and 5.9N of friction that occurs when the trainer is pulled along at a constant speed, the average is 6.0N. These are very consistent because all three results are close to the average. They are very reproducible. The same is seen for a trainer weight of 14N, where attempts 1, 2 and 3 gave results of 17.3N, 17.4N and 17.3N, these are again very close together, and therefore close to the average of 17.3N of friction that occurs when the trainer is pulled along at a constant speed. This is also more evidence to support my claim that my results are very reliable and reproducible.
As well as the above, my graph can back up my claim that my results are very reliable, as the line of best fit was very easy to draw, and it can be seen that all of my results are very close to this line. There are also o anomalies present in my results. This is because I took great care in my experiment.
Before each attempt at pulling the trainer, I was careful to ensure that there was nothing in the path of the trainer that could have obstructed its movement, items that may have done this are pens, small stones, paper etc. Whilst in the course of conducting my experiment, I kept a careful eye permanently fixed on the Newton meter. I did this in order to accurately view the reading throughout the experiment. Whilst pulling the trainer along, I tried my best to ensure that I was using the minimum force required to keep the trainer along at a constant speed.
The table -the wooden surface on which the trainer was pulled- could have affected the accuracy of my results. As it was an old table, it was worn, and therefore uneven to some degree. This could have produced inaccuracy because the table may have been worn unevenly, and therefore some parts of the surface may have produced more friction than others. Also, the table would have been worn during the course of the experiment, by the trainer rubbing along it, and although this wearing would have been to a tiny degree, it may have affected the outcome. Again, the surface could have altered during the course of the experiment, because at the start of the experiment, a slight residue of cleaning products may have remained, these may have caused the surface of the table to be lubricated, and during the course of the experiment this lubricating, if it was present, may have been rubbed off by the trainer, causing inaccurate results. The same effect may have been seen on the trainer itself, as every time I did the experiment, a small amount of the trainer's sole may have been worn off, and this would have caused a slight reduction in the amount of friction produced. Although the changes I have mentioned in this last paragraph would have been extremely small, possibly too small to be measurable on the equipment I used, they could still have had an effect on the outcome of the experiment.
Also, although I tried my best to maintain a constant force on the trainer, it is probably not humanly possible to keep the force exerted by an arm constant, and as such the results read may not have been the most accurate that is possible. Although, again, the effect of this is negligible, and therefore not likely to affect the readings that it was possible to take.
I believe that my conclusion is therefore still valid, and that my results are accurate enough to support it, and so I still believe my conclusion.
In addition, the range of my independent variable was broad, as I used 11 different weights, so my evidence is valid enough to support my conclusion.
Proposed improvements: Although I believe that both my procedure and results were accurate, I still feel that there are some improvements that I could make if I were to repeat the experiment.
As the laboratory equipment that was available was limited, I had to make do with what was available. If I was able to select the exact equipment that I wanted to make my experiment even more reliable, I would have first chosen to replace the desk used with a brand new table, which I would have liked to receive still wrapped in a plastic cover. I would have chosen to have a new table because as I stated in the reliability of my results, the on that I used to conduct my experiment was extremely worn, and a new table would have been unworn, and in perfect condition. Also, I would have used a new table of the same type for each individual experiment, as this would have provided me with a fair test, because it would have the same attributes such as roughness etc. As a new table for every single experiment is very impractical, then if I was able to remove the top layer of the table each time, leaving me with the same roughness of wood and finish each time, then that would have increased the accuracy of my results.
As stated in the section titled 'reliability of results', during the course of an experiment the sole of the trainer may have become worn, and this could have affected the experiments outcome. Therefore, the only way to prevent this wearing would be to replace the trainer after each experiment. The replacement trainer would, however, have to be of the same size, brand, and type as the original, because if the trainer was replaced with a different size, brand or type, then the experiment would no longer be a fair test, and my results would therefore be inaccurate and my experiment would be void, and inconclusive.
Instead of using my arm to pull along the trainer, I would have preferred to use some sort of mechanical arm, or similar device, to pull the trainer along. If I was able to do that, then the force would have remained perfectly constant, and the reading taken could have been much more accurate, because the device itself could have measured and indicated the force it was exerting. This would also eliminate any fatigue that could have affected my arm whilst conducting this experiment, as a mechanical device will never become fatigued.
If I were to repeat my experiment, I would ensure that I used a wider measurement range, even though I feel that the range I did use was very broad, if I were to use at least 20 different weights, possibly increasing them in 0.5N steps instead of 1N, then the results that I obtained would have been even more accurate. In addition to a broader range of weights, I could have done the experiment over different surfaces. Possible surfaces I could have used would have been lino flooring, tarmac, cement, grass, rubber, and indoor sports hall flooring. This would have given me a greater understanding of the force of friction, and also of the importance of a surface's effect on this force. In addition to a broader weight range and different surfaces, I could have experimented with different shoe types. Some options of different shoes are golf shoes, rugby/football boots, formal shoes, high-heeled shoes, hiking boots, sandals, slippers and even different types and brands of trainers. This expansion on my experiment would have provided me with different sole surfaces and tread patterns.
