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A water rocketis a type of model rocketusing wateras its reaction

mass. The pressure vesselthe engine of the rocketis usually a used

plastic soft drinkbottle. The water is forced out by a pressurized gas,

typically compressed air. It is an example ofewton!s third law of

motion. The bottle is partly filled with water and sealed. The bottle isthen pressurized with a gas, usually air compressed from abicycle

pump, air compressor, or cylinder up to "#$ psi, but sometimes

%or nitrogenfrom a cylinder.

'ater and gas are used in combination, with the gas providing a means

to store potential energy, as it is compressible, and the water increasing

the mass fractionand providing greater force when e(ected from the

rocket!s nozzle. )ometimes additives are combined with the water toenhance performance in different ways. *or example+ salt can be added

to increase the density of the reaction mass resulting in a higher specific

impulse. )oap is also sometimes used to create a dense foam in the

rocket which lowers the density of the expelled reaction mass but

increases the duration of thrust. It is speculated that foam acts as a

compressible fluid and enhances the thrust when used with e -aval

nozzles.

The seal on the nozzle of the rocket is then released and rapid expulsion

of water occurs at high speeds until the propellant has been used up and

the air pressure inside the rocket drops to atmospheric pressure. There is

a net force created on the rocket in accordance withewton!s third law.

The expulsion of the water thus can cause the rocket to leap a

considerable distance into the air.

In addition to aerodynamic considerations, altitude and flight duration

are dependent upon the volume of water, the initial pressure, therocket nozzle!s size, and the unloaded weight of the rocket. The

relationship between these factors is complex and several simulators

have been written to explore these and other factors.

&ften the pressure vessel is built from one or more used plastic soft

drink bottles, but polycarbonate fluorescent tube covers, plastic pipes,

and other lightweight pressureresistant cylindrical vessels have also

been used.

Typically launch pressures vary from /$ to "$0psi1$00 to "000 k2a3.

The higher the pressure, the larger the stored energy.

http://en.wikipedia.org/wiki/Reaction_masshttp://en.wikipedia.org/wiki/Reaction_masshttp://en.wikipedia.org/wiki/Soft_drinkhttp://en.wikipedia.org/wiki/Bicycle_pumphttp://en.wikipedia.org/wiki/Bicycle_pumphttp://en.wikipedia.org/wiki/Air_compressorhttp://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Mass_fractionhttp://en.wikipedia.org/wiki/Specific_impulsehttp://en.wikipedia.org/wiki/Specific_impulsehttp://en.wikipedia.org/wiki/De_Laval_nozzlehttp://en.wikipedia.org/wiki/De_Laval_nozzlehttp://en.wikipedia.org/wiki/Newton's_third_lawhttp://en.wikipedia.org/wiki/Nozzlehttp://en.wikipedia.org/wiki/Pounds_per_square_inchhttp://en.wikipedia.org/wiki/Kilopascalhttp://en.wikipedia.org/wiki/Soft_drinkhttp://en.wikipedia.org/wiki/Bicycle_pumphttp://en.wikipedia.org/wiki/Bicycle_pumphttp://en.wikipedia.org/wiki/Air_compressorhttp://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Mass_fractionhttp://en.wikipedia.org/wiki/Specific_impulsehttp://en.wikipedia.org/wiki/Specific_impulsehttp://en.wikipedia.org/wiki/De_Laval_nozzlehttp://en.wikipedia.org/wiki/De_Laval_nozzlehttp://en.wikipedia.org/wiki/Newton's_third_lawhttp://en.wikipedia.org/wiki/Nozzlehttp://en.wikipedia.org/wiki/Pounds_per_square_inchhttp://en.wikipedia.org/wiki/Kilopascalhttp://en.wikipedia.org/wiki/Reaction_masshttp://en.wikipedia.org/wiki/Reaction_mass

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How to build a water rocket

".In this step you will have to use an 4xacto knife to cut out the center

of the first bottle. -ook at picture to see where to cut. 5ake sure you

keep the top and bottom leftover from cutting out the center.

#.2lace the middle of the cut bottle on the bottom of the second bottle and

attach using duct tape. 5ake sure the two pieces are securely attached

6.Take the manila folder. Along the folded side, cut three triangles so

when they are opened, they appear as diamonds. *old the edges of the

fins so there is a flat piece that will be taped down to the bottle. Attach

the fins to the bottle using duct tape.7.%reating the top of your rocket is really simple. All you have to do is

take the top of the first bottle you cut and attach it to a foam cylinder

using duct tape. Then take a piece of foam and place it under the top of

the bottle. Trace the outside of the circle on the foam. %ut out the circle

with the 4xacto knife. 8se the outside as a skirt and place it around the

cylinder, attach using a stapler.

$.After creating the top, create 9 incisions using the 4xacto knife, spread

e:ually apart, around the top part of the cone. Then cut each elastic band

so they are straight lines. )lide the rubber bands through the incisions.

The first one through the first incision, and through the incision across

from it; the second one through the second incision, and through the

incision across from that; the third through the third incision, and

through the incision across from that.

2ull both sides of the elastics up over the top of the bottle and screw on

the top to hold in place.

An asterisk should appear in the inside of the top of your cone.

9.Take your garbage bag and cut the bottom off so that it lays out flat

into a big rectangle. Then cut down the center so you have two s:uares.

%ut a circle out of one of your s:uares, and there you have yourparachute.

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/. 8sing your 4xacto knife, cut a hole through the tennis ball. Take a

piece of wire and loop it through the tennis ball so it creates a handle.

Then take your parachute and put < pieces of masking tape, spread

evenly around the edge. Then punch < holes, one in each piece of

masking tape. Take your fishing line and cut < even pieces. Tie one endof the fishing line to a hole in the parachute and the other end to the

handle on the tennis ball. =epeat / times. 5ake sure the fishing line is

taut when you lift up the tennis ball in the center of the chute.

. *old the parachute in half horizontally and then again vertically. *old

the parachute into vertical triangles. After it is the thinnest you can makeit, fold it in half horizontally. 2lace the tennis ball, followed by the

parachute in the bottom of the bottle rocket.

"0. *ill your bottle between "?# way @ #?6. 2ump the air pump to

between 90 @

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that if the rocket veers off in an unexpected direction, it is less likely

to hit the operator or bystanders.

'ater rockets should only be launched in large open areas, away

from structures or other people, in order to prevent damage to

property and people.

As water rockets are capable of breaking bones upon impact, they

should neverbe fired at people, property, or animals.

)afety goggles or a face shield are typically used.

A typical twolitre soda bottle can generally reach the pressure of

"00 psi 19>0 k2a3 safely, but preparations must be made for theeventuality that the bottle unexpectedly ruptures.

Clue used to put together parts of water rockets must be suitable to

use on plastics, or else the glue will chemically DeatD away the bottle,

which may then fail catastrophically and can harm bystanders when

the rocket is launched.

Landing systems

)tabilizing fins cause the rocket to fly nosefirst which will give

significantly higher speed, but they will also cause it to fall with a

significantly higher velocity than it would if it tumbled to the ground,

and this may damage the rocket or whomever or whatever it strikes upon

landing.

)ome water rockets haveparachuteor other recovery system to help

prevent problems. Eowever these systems can suffer from malfunctions.This is often taken into account when designing rockets.

=ubberbumpers, %rumple zones, and safe launch practices can be

utilized to minimize damage or in(ury caused by a falling rocket.

Another possible recovery system involves simply using

the rocket's fns to slow its descent and is sometimes

called backward sliding. By increasing fn size, more drag

is generated. I the centre o mass is placed orward o

the fns, the rocket will nose dive. In the case o super!roc

http://en.wikipedia.org/wiki/Parachutehttp://en.wiktionary.org/wiki/bumperhttp://en.wikipedia.org/wiki/Crumple_zonehttp://en.wikipedia.org/wiki/Parachutehttp://en.wiktionary.org/wiki/bumperhttp://en.wikipedia.org/wiki/Crumple_zone

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or back!gliding rockets, the rocket is designed such that

the relationship between centre o gravity and the centre

o pressure o the empty rocket causes the fn!induced

tendency o the rocket to tip nose down to be

counteracted by the air resistance o the long body whichwould cause it to all tail down, and resulting in the rocket

ailling sideways, slowly.

"redicting peak height

If aerodynamic drag and transient changes in pressure are neglected, a

closedform approximation for the peak height of a rocket fired

vertically can be expressed as follows+

F7G

1 H peak height reached, H Initial mass of water only, H

=ocket mass with water, H Initial gauge pressure inside rocket, H

density of water, H acceleration due to gravity3 Assumptions for the

above e:uation+ 1"3 water is incompressible, 1#3 flow through thenozzle is uniform, 163 velocities are rectilinear, 173 density of water is

much greater than density of air, 1$3 no viscosity effects, 193 steady

flow, 1/3 velocity of the free surface of water is very small compared

to the velocity of the nozzle, 13 nozzle velocity remains constant until water runs

out, and 1"03 there are no viscousfriction effects from the nozzle

An independent variable that influences peak height is weight?mass.epending on the thrust of the rocket propulsion system, a rocket

re:uires a minimum mass to overcome the deleterious effects of drag.

*or example, the greater the thrust?the less the original weight of the

rocket, the more weight or mass must be added to the rocket to insure

maximum apogee. The mass is generally referred to as ballast. This

principle is demonstrated by having a student throw a straw with and

without a piece of clay attached to the !nose! of the straw. The straw

with the greater mass will travel further, provided that there issufficient thrust to overcome the ballast or extra mass.

http://en.wikipedia.org/wiki/Water_rocket#cite_note-4http://en.wikipedia.org/wiki/Water_rocket#cite_note-4

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#ulti!bottle rockets and multi!stage rockets

5ultibottle rockets are created by (oining two or more bottles in any

of several different ways; bottles can be connected via their nozzles,

by cutting them apart and sliding the sections over each other, or by

connecting them opening to bottom, making a chain to

increase volume. Increased volume leads to increased weight, but this

should be offset by a commensurate increase in the duration of

the thrustof the rocket. 5ultibottle rockets can be unreliable, as any

failure in sealing the rocket can cause the different sections to

separate. To make sure the launch goes well, pressure tests are

performed beforehand, as safety is a concern. These are very good to

make the rocket go high, however they are not very accurate and may

veer off course.

5ultistage rockets are much more complicated. They involve two or

more rockets stacked on top of each other, designed to launch while

in the air, much like the multistage rockets that are used to send

payloads into space. 5ethods to time the launches in correct order

and at the right time vary, but the crushingsleevemethod is :uite

popular

http://en.wikipedia.org/wiki/Volumehttp://en.wikipedia.org/wiki/Thrusthttp://en.wikipedia.org/w/index.php?title=Crushing-sleeve&action=edit&redlink=1http://en.wikipedia.org/wiki/Volumehttp://en.wikipedia.org/wiki/Thrusthttp://en.wikipedia.org/w/index.php?title=Crushing-sleeve&action=edit&redlink=1

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