An Extended Investigation: Bottle Rockets

Pages: 6 (1679 words) Published: September 9, 2013
Year 12-Mr Fogarty
8/23/2013
An Extended Investigation |

Liam Hallam Cameron Martin| Bottle Rockets|

This extended investigation serves to examine and evaluate the physical forces that affect the flight of a bottle rocket. This will be accomplished by altering the water levels and the level of air pressure (psi) within the rocket will be altered, and tested, to further understand the mechanics of bottle rockets. Introduction

Rocket flight has long been at the forefront of the human race’s exploration of our universe. This undeniable fact makes it necessary to study and examine the forces that act upon rockets as the fly. Given that real rockets are priced in excess of 20 million dollars, the re creation of a real life rocket’s flight is impossible. Thus the principles and rules that direct a rockets motion will be investigated as they act upon a bottle rocket. Although this may seem as far from the reality of a space exploring rocket, the bottle still acts according to the same principles of flight. A water rocket is subjected to three forces in flight; weight, thrust, and the aerodynamic force drag, all of which act on the time, intensity and height of a rocket’s flight (Benson, 2011, Online). Several equations exist that break down and gauge factors of a projectile’s motion. The equation below serves to calculate the peak height that a rocket will reach during its flight. h=MiMg2Pipg

Where,
h=peak height reached
Mi=initial mass of water only (kg)
Mg=rocket mass with water (kg)
Pi=initial gauge pressure inside rocket (kPa)
g=acceleration due to gravity (ms-1)
p=density of water (kgm3)
Before apply this formula into a rocket’s flight, its necessary to acknowledge its limitations. Firstly, this equation assumes that the  (1) water is incompressible, (2) flow through the nozzle is uniform, (3) velocities are rectilinear, (4) density of water is much greater than density of air, (5) no viscosity effects, (6) steady flow, (7) velocity of the free surface of water is very small compared to the velocity of the nozzle, (8) air pressure remains constant until water runs out, (9) nozzle velocity remains constant until water runs out, and (10) there are no viscous-friction effects from the nozzle (Schultz, 2012, Online). One of the more prominent factors that was to determine the accuracy of the gained data was the air resistance. However, after deliberation it was decided that as the size of the rocket was kept constant it was acceptable to neglect this. Also as all the tests occurred within one hour they were all subjected to the same atmospheric conditions. With the force of acceleration remaining constant (-9.8ms), the mass of the rocket will determine the overall force of weight. According to Newton’s second law F=ma Where,

m= mass of object (kg)
g= acceleration due to gravity (-9.8ms)
As water is essentially incompressible it means that it cannot hold large amounts of stored energy when pressurized. This means that the pressurized air within the rockets chamber is generating the majority of the thrust. As air can be stated as weightless, and can be compressed to huge degrees, it is a hugely effective method of generating thrust. Hence in a water rocket, the air is the air provides the stored energy, and water provides the reactive mass. As previously mentioned, the weight of the rocket will determine the downwards force acting on the projectile. This means that for the rocket to perform to its best possible ability, a balance must be found between air pressure and amount of water within rocket. The aim of this experimental report is to investigate and evaluate the effects differing water levels, and air pressure within a bottle rocket has on its flight time and peak height. As the water levels increase, the time of flight and the peak height will both decrease. This was decided as the water levels were found to dictate how much downward force is exerted on the rocket. As the air...