My aim is to investigate, when changing a variable, how far an object can travel, and how the variable I change affects this distance. I will demonstrate this by using a margarine tub, and push it across a table with the help of an elastic band. The range of variables I could change is wide. Firstly, I could modify the amount of force in newtons that I apply on the elastic band. The larger amount of force I employed on the tub, the further it would travel. I could alter the mass of the margarine tub, or its shape, size or surface area. I could alter the size or strength of elastic band, or the finish of the table, resulting in an increase or decrease of friction acting against the tub.
After carrying out a preliminary experiment, I have decided to change one variable, the mass of the margarine tub. It is important that I do not change any other variable at any time during the experiment. The pilot experiment also taught me to use the margarine tub facing downwards, so just the outside rim of the tub faced down, giving a low surface area to be combated by friction. The larger the surface area, the less distance the tub would travel due to a higher area to be slowed down by friction. I also discovered that the best distance for the tub to travel when at original mass is roughly 1.5 metres. To achieve this distance, the elastic band and margarine tub should be pulled back 85 mm before launch.
This distance should be recorded on the work surface using a piece of chalk so the experiment is a fair test. When increasing the mass of the tub, I found that increasing the heaviness of the tub in intervals of 10g left the gaps between results later in the experiment far too small. Instead, I plan to increase the margarine tub by masses of 20g. However, when putting these masses inside the tub, I discovered that a large amount of the energy stored in the elastic band was transferred into moving the masses around the tub, and not adding to the distance the tub travels. To combat this problem, I will use sellotape to stick the masses inside the tub.
To make the investigation a fair test, I must keep every variable except the mass of the tub the same or as similar as possible at all times. For example, the distance pull back the tub must be the same. This can be achieved by marking the distance with a piece of chalk, and by ensuring that I look at the back of the tub from a parallel angle. Other variables that should stay unchanged include the elastic band, the chair, the surface, the size of the tub, and the surface area it has facing down on the table. Should any of these be changed, I could record an anomalous result, however, these results cancelled out easily by recording each piece of data three times then calculating the average, therefore I need to calculate data as accurately as I can, to the nearest millimetre.
I believe that as I increase the mass of the tub, the distance the tub travels will decrease. This, I believe will be due to a lesser amount of friction acting on the lighter tube, and a heavier tub having to combat much more friction, because more energy is used up pushing the heavy tub, and not combating the friction. The friction acting on the tub looks like this:
The small “grooves” in the two objects, in this case, the margarine tub and the table, catch each other, slowing the moving object down. The smaller the amount of energy used to transport the object, the larger the amount will be used to combat the friction. The friction converts the kinetic energy into heat energy and wastes it. The difference between the energy the friction uses to attack the object and the force of energy carried by the tub is called the resultant force. Here is a diagram demonstrating this:
This is why I think the empty tub will travel a much greater distance than the tub weighing excess of 140g. Ways I could stop the friction include lubricating the surface with oil, a very smooth substance, and using a streamlined tub, which also combats friction.
The apparatus I will use includes:
Assortment of Masses
Metre Stick X 2
Table X 2
Here is a diagram of the full set of apparatus and how it will be structured:
1. I set out the equipment as shown earlier.
2. I faced the margarine tub face down and pulled it back, using the elastic band, 85mm, marking the distance with chalk. I recorded the empty tub’s distance travelled 3 times. I ensured a fair test by using a metre stick to measure, in parallel, the distance the tub had travelled.
3. I added a 20g mass to the tub, repeating the previous step.
4. I added 20g masses until I had recorded 8 results, including the empty tub.
As I pointed out earlier, my preliminary experiment helped me decide the force used on the tub, the amount the tub should increase in mass, and how far the tub should travel when empty.
Distance Travelled (cm)
Mass of object (g)
After recording the data, I constructed a line graph showing the data. A smooth curve ran through all the points except the data I had recorded for the 60g mass of tub. I re-recorded this anomalous result after the investigation in the same conditions (see above).
I have found out that the lighter an object, the further it will travel when given the same amount of force to a heavier object. The empty tub travelled much further than the tub with a 20, 40, 60 etc. mass. The heavier the tub became, the smaller the gap between each recording of data became. For example, the average results between 0 and 20g masses was 63 centimetres, yet the results between 120g and 140g was 6.5 cm. The heavier an object got, the lower the resultant force of energy. Eventually, although the curve of the graph would never quite reach 0 cm, the force of the friction would almost be equal to the force of the elastic band and tub, giving a very small result. Results support the prediction very well, and the theory that I presented seems to be correct. The reason that the graph did not form a straight line is because the resultant force got smaller and smaller as the mass of the tub got larger, and the resultant force is not in direct proportion with the mass of the tub.
The evidence obtained, mostly very accurate, included one certainly anomalous result, and another narrowly inaccurate. The procedure used in the investigation was obviously successful in the majority, yet I could have controlled the investigation more accurately be making sure not to change any other variables at all. The main factor for the inaccuracy of some of the results was probably that I did not always look at the tub in parallel when releasing it. The accuracy could have been improved by doing this, and also by taking the results 5 times then recording an average result. I could have used larger changes in masses to highlight more distinctive intervals in distance the tub travels, making it easier to pinpoint anomalous results. The evidence is, however, sufficient to support a conclusion, as only one or two results did not fit the trend, in this case, the curve.
The possibility of anomalous results was a factor leading me to take 7 results. Improvements to provide additional evidence for the conclusion could be to change the variable altered in the experiment, for example, I could use a Newton meter to change the force acting upon the tub when released, acting as an extra aspect of evidence to add to the conclusion.