Independent variable: The independent variable here is the mass of the margarine tub because I want to see how the mass affects the distance traveled.
Dependent variable: The dependent variable here is the distance travelled by the margarine tub.
Expected results
Planning B
Apparatus
1. One elastic band- to propel the object off.
2. A meter ruler- to measure the distance travelled.
3. A margarine tub.
4. Sand- to vary the mass of the object.
5. A stool- to hold the elastic band.
6. Scales- to measure the mass of the margarine tub.
7. A measurement sheet- to measure how far I pull back the elastic band.
8. A smooth surface- to carry out the experiment on.
Method
To investigate how mass affects the distance travelled by a projectile when propelled of an elastic band; I am going to experiment with a margarine tub filled with sand. I will vary the amount of sand I put in the tub to create different masses; I will use masses 50g to 500g, experimenting every 50g. I decided on this range because it will produce a large range of results which can be easily analyzed and plotted on a graph. I will stretch the elastic band around two of the legs of the stool; this will hold the elastic band taught, so I can propel the tub off of it. I will stand the stool on a large sheet of paper with centimetre measurements on it running in the direction of the elastic band; so I can measure, in centimetres how far I pull back the tub on the elastic band. I will measure from the base of the tub to make it more accurate. I will position the 0 end of the ruler at where I pull back the tub and elastic band on the measurement sheet, this way I will be measuring the complete distance travelled by the projectile. I will measure from the same end of the tub when I pull back the elastic band and when I measure how far it has travelled. I will measure to the nearest centimetre because it is the most appropriate degree of accuracy, and I will measure across with another ruler to make the measurement readings more accurate. I am using a measurement sheet rather than a Newton metre to measure how far back I pull the elastic band, because the Newton metre only went up to 10 Newton’s and this force didn’t pull back the elastic band far enough to propel the projectile a suitable distance to measure. This would make it hard for me to collect an appropriate range of accurate results. I need to make sure I don’t stretch the elastic band too much that I reach the elastic limit of the elastic band. If I do stretch the band beyond its elastic limit, as stated in Hooke’s Law, the elastic band will behave inelastically so it won’t return to its original shape.
Data Collection
The table above shows my results; I measured to the nearest half centimeter whilst I was collecting my results and worked out the average to the nearest millimetre. As you can see there is an anomaly, (81 cm for 50 grams) you can tell this is an anomaly because it is almost double of the other two experiments. This anomaly will make a difference to the average, so I will not include it in my final graph.
Data Processing
This graph shows my results and the anomaly, I plotted the points using the averages. The point at 50g is higher than it should be, so there must have been a factor which affected this result when I was doing my experiment. This graph does look similar to my expected graph that I explained, and this shows that my prediction was correct.
I took out the anomaly from my table and then calculated the average of 50g using the first two results of the 50g experiment. I then plotted another graph, but this time without the anomaly:
The trend in the graph shows that as the mass of the margarine tub increases, the distance travelled by the tub decreases. This is correct because as the mass increases the surface friction also increases; this increased friction causes the object to slow down and stop quicker and therefore in a shorter distance.
Conclusion and Evaluation
The formula for kinetic energy is: Kinetic energy = mass x velocity squared. As the kinetic energy is a constant, the line of best fit is not a straight line because of the velocity squared part of the formula; this will vary the gradient of the line of best fit. The gradient changes because you are not multiplying the velocity by a constant, but by itself so the larger the velocity, the more the number will increase by when squared. This is why the gradient is steeper at the start of the graph. The basic trend of the graph shows that the distance decreases, at a decreasing rate, as the mass increases. This is what I predicted would happen, and it was correct. I am pleased with my results and feel that they are as accurate as I could make them. I measured the distances to the nearest half centimetre because this was an appropriate degree of accuracy and made sure the ruler was in the correct position before taking each reading. If I did this experiment again, I would perhaps investigate more than one factor, and find out the effect they have on each other. For example I could investigate how far an object travels when propelled of an elastic band along an oiled or greased surface. Also I would investigate more weights so that my line of best fit is more accurate on my graph, I might also extend the range of weights to see if this made any difference. My percentage error was 14%, I worked this out using my expected table of values and my actual table of values, I used the formula Percentage error = (value – expected value / expected value) x 100. I had one anomaly whilst collecting my results, so there must have been a factor which affected this result when I was doing my experiment. This was probably a human error of misreading the length on the ruler; however it could have been any of the factors explained on the first page. Finally, I am pleased with my results and overall experiment and I feel I produced an accurate set of data.
