Fair Test:
In order to have a fair test only the height from which the ball was dropped was altered. The mass of the ball was kept constant and the flour was shaken within the container to as near a horizontal level as possible so that it did not affect the next result by causing the depth of the crater to be changed. A fair test is important to acquire precise results. In addition, I checked that the ruler was always vertical and I also made sure the calibrating stick was at the lowest point at each crater.
Measurements:
The heights dropped ranged from 15 cm to 115 cm adding 15cm in height for each time for the next reading. The number of readings taken was 7 because this is an appropriate number of readings to be able to draw a precise graph and a good range of results. Four repeat readings were taken for each height to obtain an accurate average to be used for the graph. As shown in the preliminary work, a large range of heights is required to get a satisfactory range of results. The calibrating stick was marked in cm and mm to obtain accurate results.
Scientific Knowledge:
As the 35.4g ball is raised above the flour, an upward vertical force equal to 0.354N must be applied to the object in order to lift it. The force applied will be equal to: mass x gravity and work done can be calculated as the force x height. Therefore when the ball is raised 15 cm, then Work done = force (0.354N) x height (15cm). Once the ball is raised it will have a potential energy equal to work done.
When the object is then allowed to fall it will steadily loose the potential energy it has gained and by the time it has fallen 15cm it will have lost all potential energy it previously gained. As it falls its velocity will increase due to the increase in kinetic energy. The kinetic energy it has at any instant will always equal the potential energy it has lost. As the ball falls it will accelerate due to the force of gravity. Air resistance will act upwards against the movement and when gravity and air resistance are equal, then the ball will no longer accelerate, but fall at constant velocity. Force down – Air resistance = Force (ma)
Energy is transferred when the work is done so in this case energy transferred = force x distance moved in direction of force. When it finally hits the flour the upward force of the flour is bigger than the weight.
Results:
Depth of crater - repeat readings (cm)
Trends and Patterns:
As the best fit line does not pass through the origin x is not directly proportional to y. It is however proportional to some extent. To find the proportion the constant in the equation x ∞ ky. For example with the height dropped 15cm the constant is 9.87. In calculating the constant for all the results a pattern is shown. An increase the higher it is dropped from. The exception is one anomalous result, at 45 cm which is excluded from the pattern.
Analysis:
The factor, which I decided to concentrate on for this particular experiment, was how height affected the size of a crater. In my prediction I stated that the higher up the Ball bearing the greater the size of the crater. This was based on the scientific knowledge that as the Ball Bearing gets higher it gains more Gravitational Potential Energy, therefore there is a bigger force which in turn will make the size of the crater bigger. I am pleased because by looking at the Results Table above, it is clear to see that the higher up the Ball bearing the bigger the crater. This supports what I predicted using the knowledge I already had.
Suitability of procedure and how it can be improved:
The results obtained are of good quality. There was only one anomalous result which was not too out of line which shows the accuracy of the investigation was consistent though not completely. I feel that the procedure was suitable although there are quite a few ways in which the method could be improved. A wider range of readings could be taken with a more exact reading using two decimal places or the experiment could be repeated more times for a better average.
Quality of the evidence:
Individual results were measured more accurately using a calibrating stick It was useful as it obtained readings more exactly when measuring the depth of the crater because it is harder to measure the depth precisely with a ruler. The measurements were obtained with great attention as it is important to get readings as accurate as possible to work out an average. The difficulty in taking the readings was knowing where to put the calibrating stick in to measure. The crater was quite wide therefore it was hard to see where to take the readings. This was overcome by placing a wooden stick across the diameter of the crater and placing the calibrating stick vertically from the bottom of the crater and where the calibrating stick met the stick lying across the diameter, the reading was taken. This was found to be an easier way of measurement.
Reliability of Evidence:
On the whole the overall results are reliable. Originally only 3 repeat readings were taken but to make the average more reliable a fourth repeat reading was taken. This made the average closer to the repeat readings though the average was still a little further from the repeat readings than I would have anticipated. The results increase in a linear fashion along the graph this shows that they are as I predicted. A best-fit line was drawn with some difficulty and so error bars were added to each plotted point. Keeping all variables other than the height dropped constant allowed a fair test to be performed. The range of readings was adequate but would benefit from some more readings. Suitable intervals were taken because the range of results was wide apart, they vary well and it is possible to distinguish between the points, rather than the results at each height being too close together.
Improvements:
There are many ways in which the investigation could be improved. Individual results could be made more accurate by using a more reliable source other than a hand to drop the ball from the height. The ball could be rolled off a platform at the different heights. The reliability of the data set could be improved by having a bigger range of results and more repeat readings measured using a more accurate calibration material so that results may be more accurate. The ball could be dropped with different force to see how this would change the results, the effect of speed when hitting the flour. However this may be difficult to carry out as it would have to be a fair test and to keep the force applied the same for each reading it would be difficult.
