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  Rocket Flight Calculations & Simulator
NASA's very nice work on rocket science and an impressing simulator for water rockets.

Rocket Thrust
The following links explain in detail how rocket thrust is linked to altitude/apogee.
Thrust and Mass Studies
The Internet Encyclopedia of Science


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  Soda Bottles are pressure tested but water bottles are not! Don't use water bottles for pressurized rockets. Water Rocket Pop! does not recommend pressurizing above 100 psi for safety reasons. Some people have tested burst pressures using other launch pads. This note is from an expert in pressure testing soda bottles:

I was reading a piece on a trade site for carbonated beverage bottles that said the industry has settled on a standard of two times the fill pressure for carbonated beverages (60 psi), so 120 psi would appear to be the current minimum acceptable burst pressure for the industry. When I left the industry (1986) the QA standard was a minimum burst test of 160 psi (if my memory serves me - I know that's in the range at least).

Having been lucky enough to be involved in the development of PET bottle production (1980) I would like to give you some insight into the confusion you experienced as to how your bottle failed (exploded). Relative to the neck breaking, ... the neck is not the "strongest" part of the bottle. The process of blowing the bottle from a preform orients the molecules of the PET along the axis of greatest stretch (the length), thus making the thinner areas of the bottle enormously stronger (by weight) than the thicker neck area which experiences almost no molecular orientation. Thus the neck is tougher in some aspects than the oriented material; however, it is a quite = brittle.

Also although your bottles neck failed it probably was not the first point to do so. Your picture that shows the whole bottle is a bit difficult to see details in, but having witnessed literally thousands of such tests to failure I feel pretty confident in saying that your bottle first split along the longitudinal axis. Then the forces generated by the nearly instantaneous release of pressure from the bottle most probably caused pieces of the more brittle neck to run off in all directions (to paraphrase Eugene Ionesco).

I hope this clarifies your results a little.

Best regards,

Chris Bonner
Reprinted with permission. Clarification in italics added.

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  Recycle / Reuse is a very good source of knowledge to recycling plastic, and so many other things.

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