The trajectory of a water rocket is studied in some detail.
The upward acceleration of the boost phase, downward acceleration greater than g during upward free fall motion, near parabolic motion at the top of the trajectory, and downward acceleration less than g are all visible in the trajectory.
Download video (right-click and “save link as”): Rocket.m4v . Contact us for full resolution video.
Entertaining high speed video:
NCEA & Science Curriculum
Our water rocket has been modified from the usual. The bottle neck has a bung with a 5 mm hole to extend the boost phase long enough for it to be visible in the trajectory data. Other than that, it is a standard soft-drink bottle water rocket filmed from a distance. The motion is analysed with Tracker software which we use quite a lot and strongly recommend. Note there is some distortion in the video due to camera angles.
We have a three hour activity built around the water rocket. It includes a rocket thrust test stand which we use to measure the engine thrust and then predict the speed of the rocket at the end of the boost phase and the maximum height of the rocket. The predicted speed at the end of the boost phase is reasonably accurate, but the maximum height is not. That’s instructive.
The rocket is traveling not much less than 100 km/hr on the way up and on the way down. It will do damage if it hits someone. Individual teachers are responsible for safety in their own classes.
Individual teachers are responsible for safety in their own classes. Even familiar demonstrations should be practised and safety-checked by individual teachers before they are used in a classroom.
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