Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Bottle Rocket Force 
Name: N/A
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: N/A
Question:
Where would the balance point be for a water rocket using a 2L bottle half filled with water and about 50 lbs air pressure. Would the force be concentrated near the top of the bottle as the bottle pushes against the escaping water? bottle rocket force thanks!


Replies:
Robert,

I am not quite sure what you mean by the balance point. Could you explain As far as where the force is greatest, neglecting the gravitational forces (due to the weight of the water) the force results from the pressure of the air in the bottle. Since the contents of the bottle (air and water) are fluids the pressure they exert on the bottle walls is the same everywhere and since force is the product of area and pressure the force is the same everywhere in the bottle. If you are thinking of moving the bottle by letting its contents out you will get better results by letting the water out first. In this way .... The momentum of the system is conserved. The fast moving water leaving the bottle imparts motion to the bottle. Since the bottle is losing water it is getting lighter. The (nearly) empty bottle must move much faster than the last of the water in order to conserve m momentum.
Hope this is useful.

gregory r bradburn


Click here to return to the Physics Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory