Learn more physics!
Do you have to use water in a bottle-rocket?why or why not?
- Anonymous (age 14)
OBrien middle school, Reno
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.
(republished on 07/12/06)
Follow-up on this answer.