My most recent project in physics class was to build a water rocket, demonstrating the ideas of force, mass, and acceleration (yes, Newton’s 2nd law). Though mine was not the best by far, it performed substantially above average, reaching a little over 40 meters vertically and staying aloft for about six seconds (bottle initially pressurized at 50 psi, 23% full of water). You can see in the picture that it was going fast enough upon landing to though roughly mangle the nose cone. We obtained the height measure using a bit of trigonometry; we had people who measured the angle between the ground and the rocket at its apogee (positioned a known distance on four sides of the “launch pad”), and later averaged the results obtained by this (height=distance*tan(angle)).
I had much less time to build my rocket than I would have liked, being flooded with other homework the weekend I chose to do so. So I had to scale back some, not building the parachute apparatus that I had conceived, and going with a generic but nice design. I made the fins out of card stock coated in duct tape, with a wire spine running along the edge. The latter provided me the ability to bend the fins at will, so I could induce substantial spin upon the rocket (which I did). I weighted the nose cone with colored gravel, and left strips of the 2 liter bottle uncovered so it could be seen how much water was inside (roughly 460 ml is the optimal amount).
Through watching other rockets, I got some ideas to improve my design if I am ever to make one of these things again. First, I will make a parachute, and not connect the nose cone to the rocket, so I still get much height if the parachute deploys early (the cone will keep going). I will also use shorter, thinner, stiffer, less angled fins for less drag. I found this project quite fun, and, if I have the time (unlikely), I may construct my own launch pad so I can continue to build and test new designs.
