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ejdarling
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My son & I will soon be building water + air-powered rockets for cub-scouts with soda-bottles and compressed air. You put so much water in a bottle, pressurize it, and release it upwards... Now, if nearly full of water, it would not go far, nor if nearly empty, using only air, but if optimally filled, it will go dozens, maybe hundreds of feet. How to calculate the best fill, or the height reached as a function of percentage of original volume filled with water?? A stumper so far for me, and I love Newtonian physics. Perhaps a good one for the guy who asked what is calculus good for :).
Assume the bottle will handle a certain pressure (10-15 atm?) and it doesn't have much mass relative to even a small amount of the water it could contain. How do you get started on this? If the energy is stored in the compressed air, what does the water do, anyway? It is something to "push against"? Is the instantaneous thrust equal to the pressure differential times the area of the orifice? If so, again what difference does the water make? Thanks for your thoughts, Eric
Assume the bottle will handle a certain pressure (10-15 atm?) and it doesn't have much mass relative to even a small amount of the water it could contain. How do you get started on this? If the energy is stored in the compressed air, what does the water do, anyway? It is something to "push against"? Is the instantaneous thrust equal to the pressure differential times the area of the orifice? If so, again what difference does the water make? Thanks for your thoughts, Eric