Parachutes - a Science Experiment

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Aim To investigate how parachutes work and whether size matters to performance.

Background According to Agee (2010), “As a skydiver is falling, the force of gravity is pulling them towards the earth… The parachute slows the skydiver down because it causes air resistance or drag. The air pushes the parachute back up, and creates a force opposite to the force of gravity, slowing the skydiver down.”

Question We wanted to find out how the size of a parachute would affect its descent as we felt slowing descent was integral to a parachute‟s performance – indeed, parachutes were invented to slow a person‟s fall when jumping from a hot air balloon.

Our specific question therefore was: If we change the parachute size, how will it affect the time it takes to land?

This question allows us to make a prediction (based on a scientific hypothesis), whilst also developing skills such as questioning; measuring and fair testing; recording/interpreting data; drawing conclusions and evaluating results.

This investigation links to the national curriculum‟s standard of „Scientific Enquiry‟, allowing children to learn and develop all the skills mentioned above including use of ICT. Additionally, it links to the standard of „Physical Processes‟ (specifically forces and motion). It also requires children to consider safe working environments.

Tanya Wainwright S1002106, Group 2, Cohort Z

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Hypothesis and Prediction According to Devereux (2007, p8), hypothesising is about using “previous knowledge, evidence and observations to formulate tentative theories about why things happen the way they do.” So, using our prior knowledge we hypothesised that bigger parachutes would create more air resistance. This appears to be supported by Devereux (2007, p55) who states: “The air offers a greater resisting force to objects that have a large surface area…”

Our prediction of what would happen therefore was that as the parachutes got bigger, due to increasing air resistance their descent would get slower, highlighting a direct relationship between their size and speed to fall.

We debated whether there was an optimum size beyond which this prediction would no longer hold true, but we didn‟t have the knowledge to answer this before carrying out the experiment.

Key variables Our key variables were parachute size (what we changed or the independent variable) and time to land (what we measured or the dependent variable).

Methodology  To make the parachutes we cut 5 different sized squares out of fabric (see table below), 20 equal lengths of string (approximately 40cm), tied a knot in each corner of the squares and attached 1 string to each knot.

Tanya Wainwright S1002106, Group 2, Cohort Z

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Parachute 1 2 3 4 5

Length of sides (cm) 10 20 30 40 50

Surface area (cm2) 100 400 900 1600 2500



For each parachute, we pulled all 4 strings straight and attached 2 washers to the ends with another knot.

 

We dropped the parachutes from a balcony over 5m high to allow them time to fully open. We used a digital stopwatch to measure the time in seconds for each parachute to land. This ensured accurate times were recorded.



We repeated the process 5 times per size. By repeating in this way and achieving similar results each time, we showed the results were replicable and therefore reliable.



If a parachute didn‟t open or hit something in descent, that drop was voided and repeated to avoid unnecessary anomalies in results.

Safety issues To gain the height required, we chose a balcony rather than balancing on tables or chairs. How did we devise a ‘fair test’ to ensure valid results? According to Wenham (2005, p13), for a test to be fair, all variables (other than key variables) “must be controlled, which means they must be kept the same throughout the test procedure… If [they] are not controlled, the test cannot produce a valid result.” Goldsworthy (1997, p24) explains why this is...
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