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How Does the Number of Parachutes Affect Terminal Velocity?

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Abstract

Have you ever wondered how astronauts land safely back on Earth? Many spaceships use a small crew capsule with multiple large parachutes to bring the astronauts down to a gentle landing either on the ground or in the ocean. What happens if one or more of the parachutes fails to deploy? Can the astronauts still land safely? Find out as you explore the physics of falling with parachutes in this project. 

Summary

Areas of Science
Space Exploration
Aerodynamics & Hydrodynamics
Difficulty
Method
Scientific Method
Time Required
Short (2-5 days)
Prerequisites

None

Material Availability

Readily available

Cost
Very Low (under $20)
Safety

Be careful when dropping your parachutes from high locations.

Credits
Ben Finio, PhD, Science Buddies

Thanks to Blue Origin and Ken Hess for help developing this project. 

Science Buddies is committed to creating content authored by scientists and educators. Learn more about our process and how we use AI.
https://www.youtube.com/watch?v=bv8Fgw30VkM

Objective

Determine how the number of parachutes affects the terminal velocity of a falling model crew capsule. 

Introduction

How is it possible to survive a fall all the way from space? With parachutes! A parachute helps slow an object's descent through the atmosphere. The object can be a person (Figure 1), cargo, or even a vehicle like the crew capsule from a spacecraft.

Multiple paratroopers falling through the sky with their parachutes deployedImage Credit: Capt Raymond Geoffroy / Public domain
Figure 1. People with parachutes after jumping out of a plane.

A parachute consists of a large canopy made from fabric. The canopy is attached to the load with ropes. While canopies can have different shapes, in general they all serve the same purpose. Since they have a very large surface area, they create a lot of air resistance when moving through the atmosphere. This force, also called aerodynamic drag, points in the opposite direction of an object's motion. For falling objects, this means that the drag force points up, opposite the force of the object's weight, which points downward due to gravity, as shown in Figure 2 (as opposed to, for an example, an airplane flying horizontally, where the drag force would be horizontal, opposite the direction of motion).

Diagram of a falling parachute with weight pointing down and drag pointing upImage Credit: Ben Finio / Science Buddies
Figure 2. Forces acting on a falling parachute.
https://www.youtube.com/watch?v=k_1-fmQCjWo

The drag force on an object depends on several factors, including the object's shape, area, the density of the air, and the object's velocity. As an object falls and is pulled toward the Earth by gravity, it accelerates (its velocity increases). However, as the object goes faster, the drag force gets bigger. Eventually, the upward push of the drag force exactly equals the downward force of the object's weight, and the object reaches equilibrium. According to Newton's laws of motion, since there is no net force on the object (the forces on it cancel out), it stops accelerating, meaning its velocity stays constant. When this happens, we say the falling object has reached its terminal velocity - it cannot possibly fall any faster! If you make a graph of a falling object's velocity vs. time, it will look something like Figure 3. The velocity increases quickly at first, then levels off as it approaches the terminal velocity.

Theoretical graph of terminal velocityImage Credit: Ben Finio / Science Buddies

A graph with time on the x axis and velocity on the y axis. Velocity initially increases rapidly then levels off as it approaches the terminal velocity

Figure 3. A graph of a falling object's velocity as it approaches terminal velocity (positive velocity is defined as downward).

We can predict what an object's terminal velocity will be using an equation:

Equation 1:
 

where:

Why would we want to predict an object's terminal velocity? It is very important for engineers designing spacecraft, so they can make sure the astronauts have a safe landing! Engineers also have to consider what could happen if something goes wrong. For example, they could design a vehicle to have a safe terminal velocity based on a single parachute, but what if that parachute fails to deploy? Many space vehicles have multiple parachutes so the vehicle can still land safely if one fails (Figures 4 and 5). How does the loss of a parachute affect terminal velocity? Will the astronauts be in for a rougher landing? Try this project to find out!

Apollo 15 capsule on its way to splashdown in the ocean with only 2 of 3 parachutes deployed properlyImage Credit: NASA / Public Domain
Figure 4. The Apollo 15 crew capsule landing in the ocean with only two of three parachutes properly deployed. 
Blue Origin NS-25 descending with only two of three parachutes fully deployedImage Credit: Blue Origin and Ken Hess
Figure 5. Screenshot from a video of the crew capsule of Blue Origin's New Shepard NS-25 flight during descent when one of the three parachutes failed to deploy fully. Science Buddies founder Ken Hess was on board - click here to read more about his flight! 

Terms and Concepts

Questions

Bibliography

Materials and Equipment

Experimental Procedure

Download PDF of Procedure
This project follows the Scientific Method. Review the steps before you begin.

Build Your Crew Capsule and Parachutes

Note: your capsule and parachute design does not need to exactly match the one suggested here. The project should still work with similar designs. It is OK to change the dimensions or substitute similar materials.

  1. Cut three square parachutes from flexible material like a plastic bag or tissue paper, with dimensions of approximately 20×20 cm each.
  2. Poke small holes in the corners of each parachute.
  3. Cut 12 pieces of string, each approximately 40 cm long. 
  4. Tie the end of one piece of string to each hole in the parachutes (Figure 6).
square plastic bag parachute with a string tied to each cornerImage Credit: Ben Finio / Science Buddies
Figure 6. Plastic bag parachute with a string tied to a hole in each corner.
  1. Poke three holes toward the top of your cup, equally spaced around the rim.
  2. Tie all four strings from one parachute through one of the holes. Repeat for the other two parachutes (Figure 7).
close up picture of plastic cup with strings from parachutes tied through holes around the rimImage Credit: Ben Finio / Science Buddies
Figure 7. Parachute strings tied through holes in the cup.
  1. Spread the parachutes out and make sure the strings are not tangled. Your final device should look like the one in Figure 8. 
Plastic cup with three parachutes tied to itImage Credit: Ben Finio / Science Buddies
Figure 8. Plastic cup "crew capsule" with three parachutes tied to it.
  1. Make sure your parachutes work.
    1. Pinch all three parachutes in your fingers. 
    2. Hold them up over your head as high as you can and let go.
    3. Watch your parachutes as they fall.
      1. Do all three parachutes spread out and deploy?
      2. Do any of the strings get tangled?
      3. If you are testing outside, is your capsule blown sideways a lot by any wind?
    4. Try (carefully!) standing on a chair and dropping your parachutes from a higher location. What happens?
  2. Based on your observations, modify your design if needed. Here are a few suggestions:
    1. If your capsule is being blown sideways too much by the wind, try adding a few small weights (like coins or marbles) to the cup.
    2. If the parachutes are interfering with each other, try using longer strings.

Conduct Your Drop Tests

  1. Set up a safe place to conduct your drop tests.
    1. At minimum, if conducting the tests indoors, you should stand on a chair or stepstool.
    2. If conducting your tests outdoors, you can drop your parachutes from a window, balcony, playground equipment, etc. Try to do your tests on a day that is not very windy. 
  2. Set up a tripod so your phone or camera has a full view of where you will conduct your drop tests. Make sure the crew capsule's entire descent will be visible in the video - from where you will drop it to where it will hit the ground. You will be tracking the crew capsule when you analyze your videos, so it is OK if the parachutes go out of the of the frame at the beginning. It will be easier if you have someone else to operate the camera while you do the tests.
  3. Read the section under "Supported Video Formats" on the Tracker homepage. Make adjustments to your phone's camera settings if needed.
  4. Place a meter stick so it is visible in the video frame at the same distance from the camera as where you will be conducting your drop tests. You will use this to calibrate distance in your video.
  5. Conduct at least one test drop.
    1. Start recording.
    2. Hold the parachutes up and let go.
    3. Wait for the capsule to hit the ground and stop moving.
    4. Stop recording.
    5. Watch your video to make sure the capsule remained in the frame the entire time.
    6. If needed, adjust your tripod location and/or drop height and try again.
    7. Make sure you can open your video in the Tracker software.
  6. Conduct three drop tests for three parachutes and record a separate video for each test.
  7. Cut off one of the parachutes or untie the strings and conduct three more tests with two parachutes.
  8. Repeat this process for one parachute and zero parachutes. 
  9. Transfer your video files to your computer so you can analyze them. You may want to rename the files with names that make sense ("3 parachutes trial 1" etc.).

Analyze Your Videos

  1. Your goal for this section is to produce a graph of vertical velocity vs. time for your crew capsule in each one of the drop tests. You will use these graphs to determine the terminal velocity for each test, and fill in a data table like Table 1.
Swipe left to see more
Swipe left to see more
Terminal velocity (m/s)
Number of parachutes Trial 1 Trial 2 Trial 3 Average Theoretical
0
1
2
3
Table 1. Example data table.
  1. Watch the Tracker getting started video or read the getting started page to learn how to use the software.
  2. Load your first trial for three parachutes. Track the location of your capsule as it falls, and make a graph of the vertical velocity vs. time. You should be able to follow these steps (these instructions may change if the Tracker software is updated in the future, so check their tutorials for the most up-to-date directions). 
    1. Open your video file (File→Open→File Chooser, then select your file).
    2. Select Track→New→Calibration Tools→Calibration Stick. 
    3. Drag the ends of the on-screen line so they match up with the ends of the meterstick in your video.
    4. Click the coordinate system button in the toolbar (two perpendicular red lines).
      1. Click on the coordinate axes that appear in the video frame.
      2. Change the "angle from horizontal" text box in the top menu to 180. This will point the positive y-axis down, so velocities calculated by the program will be positive as the object falls.
    5. Select Track→New→Point Mass.
    6. In the plot area on the right side of the screen, click the Plots drop-down menu and change it to 3.
    7. Click on the label for the vertical axis of the third plot. Change it to "vy: velocity y-component."
      1. Note: if you filmed your video in vertical orientation and it loaded sideways in the Tracker software, select "vx: velocity x-component" instead.
    8. Use the play bar at the bottom of the screen to advance the video to the frame where you first drop the parachutes. 
    9. Hold down the shift key on your keyboard and click on the plastic cup. This will add a data point, shown in both the video frame and on the graphs, and automatically advance the video by one frame.
    10. Continue shift-clicking to add data points until your capsule hits the ground. Make sure you click on the same spot on the cup each time. Figure 9 shows an example of what the software may look like after you have finished tracking.
screenshot of tracker softwareImage Credit: Ben Finio / Science Buddies
Figure 9. Screenshot of Tracker software.
  1. Look at the graph of velocity vs. time. Your graph may have several different regions, as shown in Figure 10. 
    1. Initially, the velocity increases very quickly as the capsule falls and the parachutes are not deployed.
    2. Velocity stops increasing as the capsule reaches its initial terminal velocity. However, the three parachutes are not yet fully deployed.
    3. Once the three parachutes are fully deployed, the velocity decreases again, and the capsule reaches its final terminal velocity.
    4. Note that the graph may be "noisy" - the line may bounce up and down a bit. That is OK - real-world data is often noisy! Even if you do your absolute best to click on the exact same spot on the cup each time, there will always be some noise in your data. The noise may also come from other sources, like the wind. 
    5. If the velocity is still increasing when your capsule hits the ground, then it did not reach its terminal velocity. Rewatch your video to make sure your parachutes fully deployed. You will need to redo your tests with a higher drop height so your capsule has enough time to reach its final terminal velocity.
Example experimental velocity dataImage Credit: Ben Finio / Science Buddies
Figure 10. Example experimental data showing different regions of the graph.
  1. Find the final terminal velocity from your graph. You can do this by drawing a horizontal line through the "middle" of the noisy data once the velocity has stopped changing. You can also calculate it mathematically by finding the average of all the data points in this region. 
  2. Repeat steps 3-5 for each of your remaining videos. Record all of your results in your data table.
    1. If your capsule does not reach terminal velocity and you are unable to test from a higher drop height, record the maximum velocity (just before impact) in your data table. Make sure you note that the value is a maximum velocity, not a terminal velocity.

Calculate Theoretical Terminal Velocity

Using Equation 1 in the Introduction, calculate the theoretical terminal velocity for each number of parachutes. You may want to make a second table like Table 2 to help with your calculations.

  1. For the mass, weigh your capsule along with the parachutes and strings. If your scale measures in grams, make sure you divide by 1,000 to convert to kilograms.
  2. Gravity will always be 9.81 m/s2 (assuming you conducted all your experiments on Earth!).
  3. You can use 1.2 kg/m3 for the density of air. Optionally, if you live at a high altitude, you can look up the density of air at your elevation.
  4. The area is the total cross-sectional area of the entire device (capsule plus the parachutes) for each trial. 
    1. The parachutes are squares, so find the total area by squaring the side length of a single parachute and multiplying by the number of parachutes (Equation 2).
    2. Assuming you used a circular cup, you can find its cross sectional area using Equation 3.
Equation 2:

where

  • A is the area in square meters (m2)
  • N is the number of parachutes
  • L is the side length of a single parachute in meters (m)
Equation 3:
 

where

  • A is the area in square meters (m2)
  • π, pronounced "pie," is the ratio of a circle's circumference to its diameter, with a value of approximately 3.14
  • r is the cup's radius in meters (m)
  1. Determining the exact drag coefficient of a shape is difficult - scientists usually find it experimentally by placing the shape in a wind tunnel.
    1. According to NASA, a typical drag coefficient for a parachute is 1.75, so you can use that for your calculation for trials with parachutes (the parachutes are much larger than the capsule, so they will be responsible for most of the drag force). Note that, unlike the area, you do not need to multiply the drag coefficient by the number of parachutes.
    2. For your trial with no parachutes, you can find many lists of drag coefficients for different shapes online. Look up a value for a shape that most closely resembles your capsule. It is OK if the shape is not an exact match (for example, you can approximate a plastic cup as a cylinder, even if the cup has tapered sides).
  2. Double-check to make sure you have all the correct units for each value in Table 2.
  3. Plug your values for mass, gravity, air density, area, and drag coefficient into Equation 1 to solve for the terminal velocity for each number of parachutes.
Swipe left to see more
Swipe left to see more
Number of parachutes Mass (kg) Gravity (m/s2) Air density (kg/m3) Area (m2) Drag coefficient Theoretical terminal velocity (m/s)
0
1
2
3
Table 2. Optional data table to help with calculating theoretical terminal velocity.
  1. Add your theoretical terminal velocity values to Table 1. Compare them to your experimental values. Are they close to what you measured?
    1. If you were unable to experimentally find a terminal velocity for some of your trials, how close is the maximum velocity you measured to the theoretical terminal velocity?
  2. Make a graph with number of parachutes on the horizontal (x) axis and terminal velocity on the vertical (y) axis. Add data points for both your experimental and theoretical terminal velocity values. 
  3. How does terminal velocity change with the number of parachutes? 
  4. What do you think the minimum number of parachutes is for a "safe landing" for a real spacecraft?
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Global Goals

The United Nations Sustainable Development Goals (UNSDGs) are a blueprint to achieve a better and more sustainable future for all.

This project explores topics key to Industry, Innovation and Infrastructure: Build resilient infrastructure, promote sustainable industrialization and foster innovation.

Variations

  • Instead of cutting them off completely, do tests where you simulate partial deployment of parachutes that do not fully expand, similar to Figures 4 and 5 in the introduction. You could do this by wrapping one of the parachutes in tape or string around a parachute to prevent it from spreading out. 
  • Parachutes come in many different shapes - can you try this project with circular parachutes instead of squares? What about rectangles or triangles? How does the shape affect the terminal velocity if you keep the area of the parachutes constant?
  • How can you make your calculation of the theoretical drag coefficient more accurate? For example, you measured the area of your square parachutes when they are laid flat, but they do not form flat squares when they fall. Can you more accurately calculate the true cross-sectional area of the parachutes (the area projected onto a plane perpendicular to the direction of motion) as they fall? 
  • Many larger parachutes have smaller "pilot chutes" that help the main parachute deploy. Can you pack the large parachutes inside the cup and use pilot chutes to deploy them?
  • How do your theoretical terminal velocities change if you do your calculations for Mars instead of Earth? You will need to look up values for Mars' gravity and atmospheric density.

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General citation information is provided here. Be sure to check the formatting, including capitalization, for the method you are using and update your citation, as needed.

MLA Style

Finio, Ben. "How Does the Number of Parachutes Affect Terminal Velocity?" Science Buddies, 25 Sep. 2025, https://www.sciencebuddies.org/science-fair-projects/project-ideas/SpaceEx_p043/space-exploration/parachute-terminal-velocity. Accessed 7 June 2026.

APA Style

Finio, B. (2025, September 25). How Does the Number of Parachutes Affect Terminal Velocity? Retrieved from https://www.sciencebuddies.org/science-fair-projects/project-ideas/SpaceEx_p043/space-exploration/parachute-terminal-velocity


Last edit date: 2025-09-25

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