What equation should I used for a water bottle rocket lab?

Question

I am using distance vs volume of water. Of course, the volume of water is my independent variable. What equation should I use for this lab?

Answer 1

According to a Wiki article, the formula for the instantaneous thrust is
F=2PA_t
where
F=thrust
P=pressure
A_t=area of the nozzle

Obviously the mass changes with time as well as the pressure. So both F, mass and P are functions of time, and you will need to integrate the resulting acceleration over time to get the distance.

Do read through the safety precautions before attempting this lab.

Ref:
http://en.wikipedia.org/wiki/Water_rocket