traducere engleza romana
Post on 12-Feb-2018
219 Views
Preview:
TRANSCRIPT
-
7/23/2019 Traducere Engleza Romana
1/7
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 -
7/23/2019 Traducere Engleza Romana
2/7
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.
-
7/23/2019 Traducere Engleza Romana
3/7
/. 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 @
-
7/23/2019 Traducere Engleza Romana
4/7
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 -
7/23/2019 Traducere Engleza Romana
5/7
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 -
7/23/2019 Traducere Engleza Romana
6/7
#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 -
7/23/2019 Traducere Engleza Romana
7/7
top related