Parachutes: Does Size Matter?

Objective

In this experiment you will test different sized parachutes to see how changes in the size of the parachute affect flight.

Introduction

In the sport of skydiving, a person jumps out of an airplane from a very high altitude, flies through the air, and releases a parachute to help them fall safely to the ground. The parachute slows down the skydiver's fall so that they can land on the ground at a safe speed. How does the parachute do this?

As the skydiver is falling, the force of gravity is pulling them towards the earth. The force of gravity can make an object fall very fast! 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. As the skydiver falls slowly to the earth, these "push and pull" forces are nearly in balance. The drag force from the parachute is slightly less than the force of gravity, so the skydiver floats slowly to the ground. In this experiment, you will test whether the size of the parachute is important for slowing down the speed of the fall. You will make a series of parachutes from small to large and test how quickly they fall from the same height. Will the large parachutes fall more slowly than the small parachutes?

As the skydiver falls, the forces of gravity and drag are in balance (SEED, 2006b).

Terms, Concepts and Questions to Start Background Research

To do this type of experiment you should know what the following terms mean. Have an adult help you search the internet, or take you to your local library to find out more!

• parachute
• air resistance
• drag
• load
• gravity
• surface area

Questions

• How does a parachute work?
• Do bigger parachutes work better than smaller parachutes?
• How will increasing the diameter of the parachute increase it's size?

Bibliography

• This project was based on two projects from the NASA Explores Program and one from the SEED program at Schlumberger:
  • NASA, 2003a. "Just 'Chute Me," NASA Explores: National Aeronautics and Space Administration (NASA). [accessed November 3, 2006] http://nasaexplores.com/show_k4_teacher_st.php?id=030519160632
  • NASA, 2003b. "Parachute Area Versus Drop Time," NASA Explores: National Aeronautics and Space Administration (NASA). [accessed November 3, 2006] http://nasaexplores.com/show_58_student_st.php?id=030509111221
  • SEED, 2006a. "Make a Parachute,"Schlumberger Excellence in Educational Development (SEED). [accessed November 3, 2006] http://www.seed.slb.com/en/scictr/lab/parachute/index.htm
• Read all about parachuting at this web site developed by the SEED program at Schlumberger. You can read about how parachuting works, the equipment that is used, and the forces of gravity and drag. You can even read about the real life experiences of people who have tried skydiving:
  SEED, 2006b. "Adventures in Skydiving," Schlumberger Excellence in Educational Development (SEED). [accessed November 3, 2006] http://www.seed.slb.com/en/scictr/watch/skydiving/index.htm
• At this site you can read about how parachutes can be used to rescue an aircraft. If you are an early reader, just click on the K-4 button at the top of the page. If you are a more advanced reader, click on the 5-8 button to read a more in-depth article:
  NASA, 2003c. "Safe Landing," NASA Explores: National Aeronautics and Space Administration (NASA). [accessed November 3, 2006] http://nasaexplores.com/show2_articlea.php?id=03-035

Materials and Equipment

• heavy weight garbage bags
• metric ruler
• scissors
• washers
• twist ties
• light weight string
• stopwatch

Experimental Procedure

1. Each parachute will be made out of the garbage bag material, so first cut open the garbage bags to make a flat sheet of plastic.
2. You will make a series of parachutes of different sizes, from large to small. Each parachute will be square in shape, so the four sides will each be of the same length. A list of sizes to try are shown in the data table below:

   Parachute	Length of Each Side (cm)	Surface Area (cm2)
   1	20	400
   2	30	900
   3	40	1600
   4	50	2500

3. Cut out each of the four differently sized parachutes from the garbage bag material. One trick is to fold the plastic sheet in half twice so that it is four layers thick. Then cut the two edges (opposite the folded sides) down to half of the length you want your square to be. When you unfold it, you will have your square!
4. Tie a knot in each of the four corners of your square. The knots will be used to anchor your string.
5. Cut out four pieces of string for each parachute. Each piece of string should be 40 cm long.
6. Tie one end of each piece of string around one of the four knots, positioning the string right above the knot.
7. Hold the center of the plastic sheet in one hand and pull all strings with the other to collect them. Tie the free end of the strings together with an overhand knot:
   
   
   
8. Attach 4 washers to the bundle of strings with a twist tie. Be sure that each parachute has the same number of washers attached, or this will alter your results!
9. Bring a stopwatch and the parachutes to a safe, high surface for your tests, about 2 meters from the ground. A good place for your test might be a secure balcony, deck or playground platform.
10. Using your stopwatch, time how long it takes in seconds for each parachute to fall to the ground. If the parachute does not open during a trial, just do that trial over so that when you are finished you have three trials which all worked. Test each parachute three times, and make an average of your data. Calculate the average by adding together your three times, and then dividing your answer by three. You can also increase the number of trials above three to get better data and organize your data table accordingly. You should keep your data in a table, and here is an example for an experiment with three trials:

    Parachute #	Trial 1 (seconds)	Trial 2 (seconds)	Trial 3 (seconds)	Average Time (seconds)
    1
    2
    3
    4

11. Now make a graph of your data. Make a line graph of surface area vs. time by creating a scale of surface area in square cm on the left side of the graph (y-axis) and a time scale in seconds on the bottom of the graph (x-axis). Then make a dot each place where your data intersect. After you connect the dots, you line may slope up or down. What does this tell you about this relationship? How does it relate to your hypothesis?

Variations

In this experiment you tested one variable, the surface area of the parachute. What other variables could be tested? Try an experiment to test these other variables:

• Load - change the number of washers to change the weight of the load
• Height - drop the parachute from different heights
• String Length - change the length of the supporting strings from short to long
• String Weight - change the type of string from thin to thick
• Material - use different material for the parachute (nylon, cotton, tissue paper, etc.)
• Shape - try making parachutes of different shapes (circle, rectangle, triangle, etc.)

Credits

Sara Agee, Ph.D., Science Buddies

Sources

This project was based on two projects from the NASA Explores Program and one from the SEED program at Schlumberger:

• NASA, 2003a. "Just 'Chute Me," NASA Explores: National Aeronautics and Space Administration (NASA). [accessed November 3, 2006] http://nasaexplores.com/show_k4_teacher_st.php?id=030519160632
• NASA, 2003b. "Parachute Area Versus Drop Time," NASA Explores: National Aeronautics and Space Administration (NASA). [accessed November 3, 2006] http://nasaexplores.com/show_58_student_st.php?id=030509111221
• SEED, 2006a. "Make a Parachute,"Schlumberger Excellence in Educational Development (SEED). [accessed November 3, 2006] http://www.seed.slb.com/en/scictr/lab/parachute/index.htm

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