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Q & A: bottle rockets

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Most recent answer: 10/22/2007
Q:
Do you have to use water in a bottle-rocket?why or why not?
- Anonymous (age 14)
O’Brien middle school, Reno
A:
You don't need water specifically. Other liquids (oil, alcohol...) should work, especially if they aren't too viscous (sticky). It's possible that some sort of fine powder might also work. You do need something fairly massive, however. Otherwise, when the very light-weight air rushes out the neck of the bottle, it carries very little downward momentum (mass times velocity). The total momentum is conserved, so that means very little upward momentum is given to the rocket. The massive fluid (like water) carries downward momentum, meaning that the rocket must get upward momentum.

Mike W.

(published on 10/22/2007)

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