This should be because if the force on an object is increased then the forced needed to move it would also have to increase.
In this experiment I will make sure that I keep everything the same except the weight of the block, as the weight is my variable. The things that I must keep the same are:
- Surface the block is sliding on
- The wooden block- because the grain of the wood would change and also the initial starting weight would be different.
- The Newton meter
- The slope of the surface
The reason that everything other than the variable must be kept the same is so that is makes it a fair test. A fair test means that we only change the one thing, called the variable, so that we can see that it is only the variable that is affecting the results.
Before we conducted our investigation we carried out a preliminary experiment. We did this so that we could test which surface would be best to use in our experiment based on the readings that we gained from the preliminary investigation. These results were as followed:
From the preliminary results it’s clear to see that the best surface to use would be foam, therefore I have chosen to use foam in my main experiment. I have chosen foam because it gave me the best range of results. From a good range of results I will be able to draw a clearer conclusion. As well as foam, polystyrene gave a good range of results but the piece of polystyrene I had was too small, because just as I got the wooden block at a constant speed it reached the end of the material. This made recording results very difficult and more likely to be inaccurate as the block may not be moving at a steady speed and therefore the results would be inaccurate.
Equipment
- Foam surface
- Wooden block
- Newton meter
- Nine 100gram weights
- Flat surface that will stay continuously at the same angle
Diagram
Method
- Firstly I am going to set up the equipment as shown in the diagram above
- I will then pull the wooden block until it is moving at a steady speed. I will do this because according to Newton’s first law of motion Newton said
This means that when an object is moving at a steady speed the two forces acting on the object are equal. I will use this information to record the force of friction because when I pull the block my pulling force will be measured on the Newton meter, so therefore if the block is moving at a steady speed the force of friction will be the same as my pulling force.
- Once the block is moving at a steady speed I will record the results.
- I will then repeat this but place one of the 100g weights on top of the block, so as to increase the weight.
- Once I have added the extra weight I will pull the block across the foam until yet again it is moving at a steady speed.
- I will again record the results.
- I will continue adding the weights one at a time until all of the weights have been used up and I will record the results each time.
The experiment will be carried out three times; this was done to make the results more accurate. It makes the reading more accurate as it is averaged out.
To ensure that my experiment is carried out in the safest way possible I will conduct it in the middle of the table so that the weights do not fall off the table and onto any part of my body.
Results
Analysis
On the previous page was my graph to show the results from the investigation. I showed that as the weight of the block increases the force of friction acting on the block also increases. From first looking at my graph it looks as though my prediction was incorrect because the force does not double when the force is doubled. On a closer inspection however you can see that the graph does not start at zero. Therefore you need to rearrange the equation y = mx + c. you must do this because is the graph was to continue backwards then the line would eventually cross the x line. When it does the equation for the line is y – c = mx. C stands for the frictional force present on the block even when there are no weights on top of it. This force is here because the block still has weight even though there are no weights on top of it. The C must be taken away from the force that has been recorded. Once this has been taken away it will be able to see if my prediction that the weight is doubled then the force of friction is doubled is right. Here are some examples to explain this:
Y – C = mx
5 – 0.9 = 10.1 – 2.6
4.1 = 7.5
y – C = mx
2 – 0.9 = 4.6-2.6
- = 2
These calculations are done using the figures from my graph. There are lines on the graph to indicate where I got these statistics.
From these examples you can see that my prediction was in fact correct as the weight or original force increases the force of friction increases by the same amount.
Evaluation
I feel that, my results were relatively accurate though I do feel that they could be improved by having a Newton meter that has more accurate readings. For this experiment however I think that the results are accurate enough to prove the theory and my prediction. The force of friction did in fact double when the weight of the object was doubled. This reverts back to my prediction and the workings of Leonardo da Vince and another man called Guillaume Amontons. He said
“The friction made by the same weight will be of equal resistance although the area of contact may be different lengths and breadths; the friction produces double the amount of effort if the weight is doubled.”
Amontons said that he noticed patterns of behaviour when two surfaces moved against each other. He said that the roughness of the surfaces was to blame for this. They were proved to consist of minuscule dip, mountains and cavern that interlock with each other as they pass over one another. By raising the upper object, in this case it is the wooden block; you would reduce the amount of friction. So therefore by pushing harder on the upper object you would increase the friction and a greater force would be needed to pull the block and this proves my results and my prediction.
