Aerodynamic Water Rocket with Center-of-Pressure Fins
An engaging, screen-free learning activity that builds real-world creativity and critical thinking for kids aged 7 to 9.
Materials Needed
- • Clean 2-liter PET carbonated beverage bottle (not non-carbonated) (1)
- • Stiff coroplast sheet or rigid plastic cardboard (1 sheet (30x30cm))
- • Heavy-duty duct tape (1 roll)
- • Solid rubber stopper #4 pierced with sports inflation needle (1)
- • Bicycle floor pump with pressure gauge (1)
- • Water source (1 liter)
Pro Tips
- → Do NOT fill the bottle completely with water—optimum thrust ratio is exactly 1/3 water and 2/3 compressed air.
- → Fins MUST be placed low at the nozzle base to drag the Center of Pressure well behind the Center of Mass.
- → Pressurize slowly with a bicycle pump until the rubber stopper pops out with an exhilarating supersonic hiss!
Safety First
Launch in a wide open field away from buildings. Everyone stands 5 meters back during pressurization.
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Step-by-Step Instructions
Step 1
Cut three identical triangular fins from rigid plastic card or coroplast, angling the leading edges for minimum aerodynamic drag.
Step 2
Tape the fins symmetrically 120-degrees apart near the bottle nozzle using high-tensile duct tape, ensuring perpendicular alignment.
Step 3
Push a standard inflation needle through a #4 solid rubber stopper, insert the stopper firmly into the bottle nozzle filled 1/3 with water, and connect the bike pump.
Step 4
Invert the rocket onto an outdoor launch stand, clear all bystanders 5 meters away, and pump steadily until pressure overcomes the stopper seal for liftoff!