Measuring Drag On Shape-Morphing Objects

ISEF Category: Physics and Astronomy

Subcategory: Mechanics  ·  Difficulty: Intermediate  ·  Setup: Home Setup  ·  Time: 1 to 2 Months

The Hook

A shape that changes form can change how fast it falls, and that matters for soft robots, deployable structures, and even rescue devices. Your project turns that idea into numbers. Instead of guessing which shape slows down more, you can measure drag coefficient and plot how it shifts as the object extends or compresses. That gives you a real design curve, not just a cool demo.

What Is It?

Drag is the push from a fluid, like air, water, or syrup, that resists motion. The drag coefficient, often written as Cd, is a number that helps compare how “slippery” or “pushy” different shapes are in a fluid. A low Cd means the object moves through the fluid more easily. A high Cd means the fluid pushes back more.

Your shapes are not fixed. They morph. A waterbomb-base origami form or a Kresling tower can extend, collapse, or twist, which changes the area facing the flow and the way fluid swirls around it. Think of it like changing the size and angle of a hand in wind. A flat hand feels more resistance than a narrow edge, even though both are still your hand.

This project asks how much that changing shape changes drag. You can test the object in air during free fall, or in water, or in a thick fluid like glycerin or honey. Then you can build a curve that links extension or compression to Cd. That curve is useful because it connects shape to motion in a way you can measure and compare.

Why This Is a Good Topic

This is a strong science fair topic because you can change one thing at a time, measure a clear output, and connect your result to real design problems. Shape-morphing objects appear in soft robotics, deployable structures, and impact protection, so your work has a real-world link. You can learn fluid drag, experimental design, video analysis, and basic modeling without needing a university lab. The topic also leaves room for originality, since you can compare shapes, fluids, and extension states in many ways.

Research Questions

• How does extension level change the drag coefficient of a waterbomb-base origami object?
• What is the effect of Kresling tower twist angle on drag coefficient in a fluid test?
• Does fluid thickness change the Cd-vs-extension curve for the same morphing object?
• To what extent does orientation relative to flow change drag for a compressed versus extended shape?
• Which morphing geometry, waterbomb-base or Kresling, produces the largest Cd change across the same extension range?
• How does surface roughness affect drag on a shape-morphing object at the same extension state?

Basic Materials

• Origami paper or thin cardstock for test objects.
• Clear plastic sheet or laminated paper templates for repeated builds.
• Honey, glycerin, or corn syrup for a thick-fluid test medium.
• Tall clear container, tube, or homemade drop column.
• Smartphone with slow-motion video.
• Meter stick or ruler with visible marks.
• Kitchen scale with 0.1 g accuracy.
• Tape and waterproof marker for labeling.
• Stopwatch or video frame counter.
• Large tray or towels for spill control.

Advanced Materials

• Force sensor or load cell for direct drag measurements.
• Motion tracking target marks for video calibration.
• Transparent water flume or recirculating tank.
• Variable-speed pump or flow control setup.
• Vernier calipers for geometry measurements.
• Digital balance with 0.01 g accuracy.
• 3D-printed molds or frames for repeatable morphing structures.
• High-speed camera.
• Viscometer or density meter for fluid properties.
• Particle tracking beads or dye for flow visualization.

Software & Tools

• Tracker: Tracks motion frame by frame and helps you estimate speed and acceleration from video.
• ImageJ: Measures shape dimensions and pixel-based area changes in still images or video frames.
• GeoGebra: Helps you graph Cd against extension and fit curves to compare designs.
• Python: Organizes repeated trials, calculates averages, and runs regression tests.
• Google Sheets: Stores trial data, builds charts, and checks for outliers quickly.

Experiment Steps

1. Define the exact morphing geometry you will test and choose one measurable extension variable, such as height, twist angle, or projected area.
2. Plan how you will keep mass, material, and release method as constant as possible while only changing shape.
3. Choose one measurement method first, either free-fall video analysis or flow-tunnel force testing, so your data are comparable across trials.
4. Build a calibration plan that turns video pixels, travel distance, or force readings into physical units.
5. Design controls that separate shape effects from fluid effects, including a fixed-shape reference object and repeated trials.
6. Decide how you will convert your raw measurements into Cd, then graph Cd against extension and test for trends.

Common Pitfalls

• Changing the release angle between trials, which adds spin and makes drag look inconsistent.
• Using a morphing object that does not return to the same shape every time, which breaks repeatability.
• Forgetting to measure the fluid properties, which makes Cd comparisons across honey, glycerin, or water unreliable.
• Letting bubbles, wobble, or wall contact affect the fall path, which hides the real drag signal.
• Mixing projected area and extension without a clear definition, which makes the final Cd-vs-extension curve hard to interpret.

What Makes This Competitive

A stronger project goes beyond “which shape falls slower.” You can earn more credit by defining Cd carefully, measuring shape changes with video or image analysis, and repeating trials across several fluids or flow speeds. A competitive version also compares at least two morphing geometries and uses statistics to test whether the differences are real. If you connect your results to a simple design rule for soft-robotic bodies, your project starts to look like engineering research, not just a demo.

Project Variations

• Test the same morphing object in water, glycerin, and honey to compare how viscosity changes the drag curve.
• Compare a 2D folded strip with a 3D Kresling tower to see how dimensionality changes drag response.
• Track projected area from video, then compare area-based predictions with measured Cd to see where simple models fail.

Learn More

• NASA Glenn Research Center Beginner's Guide to Aerodynamics: Search NASA for drag, lift, and basic flow explanations written for students.
• MIT OpenCourseWare Fluid Mechanics: Search MIT OpenCourseWare for lectures and notes on drag, Reynolds number, and boundary layers.
• NOAA National Data Buoy Center educational pages: Search NOAA for basic fluid flow and wind measurement resources that help with outdoor analogs.
• Physics of Fluids: Search the journal for review articles on drag, shape change, and low Reynolds number flow.
• PubMed: Search for review articles on soft robotics, deployable structures, and fluid-structure interaction.
• ImageJ Documentation: Find the free manual and tutorials through the ImageJ project site for measuring shape changes from images.