There are many variables which could affect the outcome of this experiment:
- Weight on the parachute
- Construction materials
- Drop height
- Shape of the parachute
- Size of the parachute
- Length and number of suspension lines
- Environment i.e. Drafts, heat etc.
As we decided to investigate if the canopy size affects the time it takes to fall, our independent variable in the size of the canopy.
The dependent variable is what we are measuring, which is the time it takes to fall to the ground in seconds, we expect this to be dependent upon the canopy size in our hypothesis.
Our controlled variables are all of the variables which we are going to keep constant:
- Length of suspension lines at 30cm each, 4 lines on each parachute.
- Construction materials: black bin liner bag plastic for the canopy, square shaped with the suspension lines attached at each corner with a small amount of cellotape, the same thickness of threads for the lines.
- The same weight used on both parachute, a metal clip weighing 8.7grams.
- Height at which the parachute is dropped, 3.1meters, and the same individual to release the parachute dropper, this controls user reaction times, and mechanism release time.
- Same location for the experiments, this ensures that they are conducted in the same environment.
- the same timer and user to time the descent time, this again controls the reaction time and ensures the same accuracy, the timer operator was led on the floor so that her eye level was at ground level to identify exactly when the parachute touched the ground, therefore when to stop the timer.
- the centre of the parachute always put into the parachute droppers clip, this ensures that it is the same point on the canopy that is always at the highest point at the time of release,
Photographs of the experiment location, and the parachutes constructed and used in the experiment can be found in Appendix One.
“The control variables constitutes a fair test.” (Peacock, 1999, p.12) To ensure the investigation is controlled, the only variable that changes is the independent variable, all others are controlled. This should result with it only being the independent variable that affects the dependent variable. As stated by Goldsworthy & Feasey (1997, p.24), “taking care to ensure as fair a test as possible will give you more confidence in your results.”
To get accurate and reliable results, we decided to conduct the experiment ten times for each parachute. Peacock, (1999, p.13) suggests that this should be done to ensure the final result is more accurate, so that you can identify any ‘fluke’ results, and so that anomalous measurements can be identified by looking at the trend.
The measurement was measured in seconds using a digital stop clock. We initially began the experiment with a larger metal clip, however we found that the parachute was falling too fast for us to measure time accurately. The decision was made to use a smaller weight to enable us to measure the time more precisely.
Our method was the same for each parachute size and for each drop. See Appendix Two for details of the method.
The results were placed into a table as this allows the data to be easily recorded, and analysed. A scatter graph was also constructed using the table and trend lines were calculated by the use of ICT.
(Larger copy available in Appendix Three)
The decision to display the data on a scatter graph is because as stated in Goldsworthy & Feasey (1997, p.37) there is a “general relationship towards the independent variable and the dependent variable.” Graphs are useful as patterns and trends can be easily identified, also anomalous results can be easily identified and reasons behind them can be analysed.
The graph shows that as the parachute size increases, so does the time taken for the parachute to fall. The graph also shows that the results are rather constant as neither of the trend lines has a significant gradient.
The majority of the results are following the same pattern for both parachutes. The most prominent anomaly is drop number six on the 15x15cm parachute. This may have been down to an error in the method or due to reasons out of our control, such as a door being opened in the classroom.
The results support the originally prediction and hypothesis. Parachutes with a larger sized canopy take longer to fall to the ground. The hypothesis is therefore correct. The results support the theory that air resistance is increased by enlarging the size and area of the canopy as stated by Creary et al. (1997, p.103) The affect of this is that the parachute takes longer to fall to the ground, as there is more upward force acting on it.
The results show an example of a controlled test, with a nice, accurate set of results which appear to be reliable. However during the experiment, I identified areas for improvement, which would make the experiment even more controlled and therefore accurate. Some aspects were out of our control therefore they are limiting factors to consider.
Limiting factors and areas for improvement include:
- A more controlled environment for the experiment to be conducted in, i.e. fewer people in the room so drafts are avoided as these could affect the parachutes fall.
- More drops of each parachute, to give a more reliable result.
- A higher drop height, hence reducing human error with reaction times.
- Technological equipment to record the drop time exactly.
- I felt that the way the suspension lines were attached to the parachute could be improved on vastly.
- The weight could be improved; an actual weight would have been more suitable than a metal clip. Also the suspension lines may not have been exactly in the centre of the clip, causing the parachute to be off-centred.
- The larger parachute would have had a greater total weight due to more plastic used in construction; this should have been minimal due to the materials used.
Extension investigations could be carried out with canopies of even more sizes, to perhaps see if there is an optimum size of canopy? Different variables such as the materials used and shapes could also be investigated.
Some of the variables are particularly difficult to control, such as a draft in the room may result in the parachute taking longer to fall, hence results would be lacking reliability. There are methods as explained above to try and combat this issue. The combined total weight of each parachute also could have an impact upon the results. During the experiment this was not considered, this highlights the importance of thorough planning in science investigations and supports the idea of carrying out pilot test before conducting the final experiment. Science is however a subject whereby there are always alternative avenues to explore, which mean to conduct an experiment that is one hundred percent reliable, is virtually impossible. All that can be done is the identification of all of the variables and all reasonable steps taken to keep the control variables constant.
References
Creary, C., Dunne, D. & Wilson, G. (1997) Forces. Northampton: NIAS, Northamptonshire County Council Education and Libraries.
DfEE & QCA. (1999) The National Curriculum. London: Department for Education and Employment, and Qualifications and Curriculum Authority.
Goldsworthy, A. & Feasey, R. (1997) Making sense of Primary Science Investigations. Herts: The Association for Science Education.
Peacock, G. (1999) Teaching Science in Primary Schools. Essex: Progressive Printed Ltd.
Appendix One
Parachute
15cm x 15cm
Parachute
30cm x 30cm
Both parachutes The metal clip can
together: as can be be seen, along with
seen, cellotaping the suspension lines
the suspension lines is which are just
not very controlled and clipped into the
consistent on both centre of the clip.
parachutes and all
corners.
With the limitations of the classroom, it was difficult to maintain a constant height. Hence the decision to use a cupboard with the dropper on top was made to try and maintain a constant height.
.
Appendix Two
Construction of the parachutes.
We measured each canopy using a ruler and cut out the correct size using scissors. We folded the square diagonally twice so that we could accurately find the centre of the canopy; we marked this with a pen mark. The suspension lines were measured with a ruler and cut to the appropriate lengths, they were then cellotaped into the corner of each parachute, on the inside of the canopy. Each time they were cellotaped in the same manner as feasibly possible. The metal clip was attached to the bottom of the parachute by placing the 4 suspension lines into the clip in the centre.
Conducting the Experiment
The centre of the parachute was placed in the parachute dropper, and this then placed upon a cupboard. Jessica then released the mechanism and said go as she released. At this point Lisa started the stop clock. As soon as the parachute touched the ground, Lisa stopped the clock and the time was recorded by myself. This was repeated ten times for each parachute. We had another member of the group, Sarah who oversaw the experiment and tried to control the environment i.e. stop others from walking past as we dropped and timed the parachute.
Appendix Three
Appendix Four
Bibliography
Full list of resources consulted during this assignment.
Creary, C., Dunne, D. & Wilson, G. (1997) Forces. Northampton:
NIAS, Northamptonshire County Council Education and Libraries.
DfEE & QCA. (1999) The National Curriculum. London: Department for Education and Employment, and Qualifications and Curriculum Authority.
Goldsworthy, A. & Feasey, R. (1997) Making sense of Primary Science Investigations. Herts: The Association for Science Education.
Hallam, G. (ed.) (2004) Key Stage Two Science – The Study Book. 3rd edn. Newcastle upon Tyne: Coordination Group Publications Ltd.
Henderson, T. (1996-2007) ‘Lesson 3: Newton's Second Law of Motion,’ The Physics Classroom Tutorial. [Online] Available at http://www.glenbrook.k12.il.us/GBSSCI/PHYS/CLASS/newtlaws/u2l3e.html (Accessed: 8th November 2008)
Peacock, G. (1999) Teaching Science in Primary Schools. Essex: Progressive Printed Ltd.
