Railgun Physics
The underlying physics involved in the railgun are rather
simple. Current flowing through an inductor creates a magnetic
field. The current flowing through the field creates a Lorentz
force on the inductor tending to push the coil apart. If one
portion of the coil is free to move, this portion will slide away
from the power source.Qualitatively, its a relatively
straightforward process. Difficulty arrises in trying to
quantitatively determine the time dynamics of the electric and
magnetic fields present, and an analytical description of the
motion of the slug. To do so, we must examine the relationship
between the current in the loop, the induced magnetic field, the
motion of the slug, and the geometry of the loop - all as functions
of time.
We will break down the complex problem of determining the
analytical equations of motion for the slug in the following
way:
Determine the instantaneous induced magnetic field at any point
as a function of loop geometry and current in the loop at a given
time.Take Faraday's Law and derive the equation for the induced EMF
in the loop. Calculate this based on the magnetic field, determined
above.Solve Ohm's Law for an analytical formulation of current as a
function of loop resistance, initial charge in the capacitor(s),
capacitance of the power cap(s), and induced EMF. Take the
derivative of this equation to get an equation for I'(t) with no
integrals in it.Now we need to replace I(t) and I'(t) in the above
equation with something we know how to calculate. To do this, we'll
first manipulate the Lorentz Force law like this:Determine the
instantaneous magnetic field at any point on the slug as a function
of loop geometry and current in the loop at a given time.Integrate
the magnetic field over the length of the slug and multiply by the
instantaneous current to reveal the magnitude of the Lorentz Force
at a given time.Set the Lorentz Force magnitude equal to mL"
(F=ma). Solve this equation for I(t) and take its time
derivative.Now we have have two equations for I'(t) which we can
set equal to each other, leaving a differential equation for L(t).
Solve this differential equation to reveal the time evolution of
L(t) [position of slug on rails], L'(t) [velocity of slug], L''(t)
[acceleration of slug], etc.1) Magnetic field in the current
loop
Assuming we know the shape of our current loop and the magnitude
of the current at a given instant, the instantaneous magnetic field
caused by the current in the loop is given by the Biot-Savart law
(Griffiths 5.28):
Where r is the vector from the source (dl) to the point at which
we are evaluating the field. We can expect the displacement current
term of Ampere's law,
to affect our magnetic field, because we expect to see an
electric field that changes with time. However, its contribution is
scaled by the permittivity of free space, a factor ~10-11. This
means that in order for the displacement current to noticably
affect the magnetic field, the change in electric field would have
to be on the order of 1011 V/m s.
This would entail a change in voltage in the circuit of Px1011
V/s where P is the perimeter of the current loop. In the highly
unrealistic case of a 10kV power source (much higher than we're
likely to use), a loop perimeter of 0.1m (tiny) and a firing relay
that switches in 1 milliseconds (unreasonably fast!!), the
displacement current is then on the order of 1 Amp, but we are
expecting power supply currents possibly as high as ~10000 Amps
initially, making the displacement current contribution to B
inconsequential.
Therefore, to get a value for B(t), we break the Biot-Savart
integral up into four parts - the two rails, the slug, and the
connection opposite the slug which we will approximate as a fixed
armature across the rails. In reality, this connection will consist
of the power source, the firing relay, and the connecting wires.
Our assumption is that the field contribution of this portion of
the circuit can, in fact, be manipulated to be very similar to a
direct connection across the rails.
The direction of the magnetic field vector depends on which
direction the current flows through the loop. For convenience,
we'll assume that the current moves counter-clockwise. By the
right-hand rule, the magnetic field is in the positive z direction,
"up".
The magnetic field at some point, P, induced by current flowing
through a straight wire can be derived analytically. A succinct
example of this derivation is given in Griffiths, chapter 5,
example 5. The following figure is taken from this example.
The end result is that
B = (mu0I/4z*pi) * [sin(theta2) - sin(theta1)]where z is the
shortest distance from P to the wire, theta1 and theta2 are the
initial and final angles between z and r. We will approximate the
railgun as four straight wire field contributions summed
together.
For the first rail:
z = ysin(theta1) = -(L - x) / sqrt((L - x)2 + y2)sin(theta2) = x
/ sqrt(x2 + y2)For the second rail:z = (W - y)sin(theta1) = x /
sqrt(x2 + (W - y)2)sin(theta2) = -(L - x) / sqrt((L - x)2 + (W -
y)2)For the slug:z = (L - x)sin(theta1) = (W - y) / sqrt((W - y)2 +
(L - x)2)sin(theta2) = y / sqrt(y2 + (L - x)2)For the "back"
connection:z = xsin(theta1) = -y / sqrt(x2 + y2)sin(theta2) = (W -
y) / sqrt(x2 + (W - y)2)where L is the length of the rail to the
slug, W is the rail separation, while x and y are the coordinates
of the point inside the loop for which we are calculating the
field. Plugging these four sets of values into the equation above
and summing the results leads to the following analytical solution
for the magnetic field at some point inside the loop:
Oops, screwed that equation graphic up bad. It's all wrong, but
the general form is right. it's B(I,x,y,L,W)|slug =
(mu_oI/4pi)[f(L,W,x,y)]
2) Inductive EMF in Current Loop
Faraday's law tells us that when we have a changing magnetic
field, we have an induced electric field.
We take Faraday's law and act upon it with the curl theorem of
vector calculus,
to achieve the following relation for the induced EMF,
epsilon:
Again, this has been done analytically with Mathematica. [NOTE:
Our initial railgun derivation used a slightly different form for
epsilon, Griffiths 7.13. This is basically the same equation except
the time derivative is pulled outside the integral because the
magnetic field is assumed to be constant in time. This is obviously
not the case for the railgun, and therefore the original derivation
was incorrect.]
3) Ohm's Law
The induced EMF, calculated in section 3 above, opposes the
power source voltage and therefore decreases the circuit current
via Ohm's Law:
V(t) = I(t)R = V(t)power supply - epsilon(t)Where R is the
circuit resistance. We'll assume that the resistance is constant
with time, and we'll hope that it is very small. For this
derevation, we will also assume that the power supply is a
capacitor. This leads to the canonical form for I(t):
I(t) = (1/R)[Vcap - epsilon(t)]The capacitance of a capacitor is
given by
C = q(t)/V(t)where q is the amount of charge on the capacitor
and V is the voltage across the capacitor. The charge at any time
is given by
q(t) = q(0) - integral[I(t)dt]Now we can write the current like
this:
I(t) = (1/R)[(q0 - integral[I(t)dt])/C - epsilon(t)]Now we can
take the derivative of this equation with respect to t to get a
differential equation of I.
I'(t) = (1/R)(de/dI) - I(t)/RCSome thought needs to be given to
bounday conditions here, since the factor of q0/RC has
disappeared.
4) The Lorentz Force
The current in the loop flowing through magnetic field
calculated in part 1 generates a Lorentz force outwards on the
loop. The Lorentz force on the slug can be calculated analytically
(Griffiths 5.17):
Fmag(I,L,W) = I(t) * integral[dy x Bslug(I,y,L,W)]The magnetic
field in this equation is given the subscript 'slug' because we are
only interested in the field at the slug. This is the only part of
the field that contributes to the Lorentz force on the projectile
itself.
To calculate this magnetic field, we'll use the same technique
and assumptions used in part 1. However, we can simplify the
analysis here a bit since we'll always be at x=L. Also, the
contribution to the field from the slug itself can be ignored.
Intuitively, if the slug were just a piece of straight wire, no
amount of current through that wire would cause it to move anywhere
in the absence of external fields. In the actual system, where the
slug is under the influence of large magnetic fields, it can still
be shown that the slug current won't move the slug. It's a simple
matter of momentum conservation. If the slug moves itself, then
momentum has been created from nothing.
Since the magnetic field is uniformly vertical and the slug lies
horizontally on the rails, it is clear that the direction of the
force will be horizontal and perpendicular to the slug, i.e. in the
x direction. The cross product coveniently drops out, and all
vectors becomes scalars with the exception of an x-hat at the
end.
Fmag(I,L,W) = (mu0L(t)I(t)2/pi) * (W2+L(t)2-L(t)*sqrt(W2+L(t)2))
/ sqrt(W2+L(t)2)This is also equal to the mass of the slug times
the acceleration of the slug (Newton's 2nd law of motion, F=ma).
The acceleration of the slug can be written as the second time
derivative of L, leading to this equation:
m * L''(t) = (mu0L(t)I(t)2/pi) * (W2+L(t)2-L(t)*sqrt(W2+L(t)2))
/ sqrt(W2+L(t)2)This equation can be solved for the current:
I(t) = sqrt[pi * m * L''(t) * sqrt(W2+L(t)2) / (mu0 * L(t) *
(W2+L(t)2-L(t) * sqrt(W2+L(t)2)))]5) Differential Equation of
Motion
The results from parts 4 and 5 can be combined to replace all
instances of I(t) and I'(t) and leave a differential equation in
terms of L(t), L'(t), L''(t), etc. (slug position, velocity,
acceleration, etc)
It is hoped that Mathematica will be able to solve this
differential equation to give an analytical form of the equations
of motion for the slug in terms of physical variables like the mass
of the slug, rail separation, and capacitance.
This will represent the end of the theory effort for the railgun
and we will then proceed to design considerations and begin
construction. (assuming, of course, that the numbers don't indicate
that we require 1000 Farads of capacitance or one million volts or
something.)
Picture this: A massive destroyer receives the location
coordinates of an enemy headquarters more than 200 miles away.
Instead of launching a million-dollar Tomahawk cruise missile, it
points a gun barrel in the direction of the target, diverts
electric power from the ship's engine to the gun turret, and
launches a 3-foot-long, 40-pound projectile up a set of
superconducting rails. The projectile leaves the barrel at
hypersonic velocity--Mach 7-plus--exits the Earth's atmosphere,
re-enters under satellite guidance, and lands on the building less
than six minutes later; its incredible velocity vaporizes the
target with kinetic energy alone.The U.S. Navy is developing an
electromagnetic railgun that will turn destroyers into
super-long-range machine guns--able to fire up to a dozen
relatively inexpensive projectiles every minute. The Navy is
collaborating with the British Ministry of Defence, which has a
similar effort under way. In 2003, its facility in Kirkcudbright,
Scotland, hosted a 1/8-scale test of an electromagnetic railgun
that produced stable flight in a projectile fired out of the barrel
at Mach 6. But Capt. Roger McGinnis, program manager for directed
energy weapons at Naval Sea Systems Command in Washington, D.C.,
estimates the U.S. version won't be "deliverable" until 2015 at the
earliest.The technology behind the electromagnetic railgun has been
around for more than 20 years, but early efforts wilted because of
the huge power requirements: No ship could generate or store enough
electricity to fire the gun. The concept was revived a few years
ago when the Navy announced plans for its next-generation
battleship, the all-electric DD(X). "In the past, destroyers had 90
percent of their power tied to propulsion," explains McGinnis. "But
with DD(X), you can divert the power to whatever you need. We can
stop the ship and fire the railgun as many times as we need, then
divert the power back to the screws."The barrel of the
electromagnetic railgun will contain two parallel conducting rails
about 20 feet long, bridged by a sliding armature. In the current
design, electric current travels up one rail, crosses the armature,
and heads down the second rail. The loop induces a magnetic field
that pushes the armature, and the projectile aboard it, up the
rails.The challenges that remain include ensuring that the gun can
target enemy sites with precision, and creating equipment that can
withstand the gargantuan pressures the gun will create. "Right now,
guns are only as accurate as the targeting of the bore, and now
we're talking about 200-plus-mile ranges, so there has to be
aerodynamic correction," says Fred Beach, the assistant program
manager for the electromagnetic railgun at Naval Sea Systems
Command. The projectile, he says, will receive course correction
information from satellites and will steer itself with movable
control surfaces. And because the projectile will be subjected to
up to 45,000 Gs during firing, the onboard electronics must be
strengthened to withstand the acceleration. Forces inside the gun
itself--particularly getting the armature to move easily within the
system--are also challenging the designers. "Getting two pieces of
metal to slide past each other is pretty hard--we're getting a lot
of damage to the rails," Beach says.The electromagnetic railgun's
projectiles will cover 290 miles in six minutes--initially
traveling 8,200 feet per second and hitting their target at 5,000
feet per second. Current Navy guns, which shoot powder-ignited
explosive shells, have a maximum range of 12 miles and, because
they are unguided, are difficult to aim. Though guided missiles,
the current long-range alternative for destroyers, can achieve
ranges comparable to that of the electromagnetic railgun, their
cost and storage problems are what's driving the efforts to find an
alternative. Ships can only carry up to 70 guided missiles and must
return to port to restock because the missiles cannot be loaded at
sea, whereas railgun projectiles can easily be loaded at sea, and
by the hundreds. Also appealing is that the electromagnetic
railgun's missiles do not contain volatile explosives; the weapon
does its work with kinetic energy.
How Do Rail Guns Work?
The electromagnetic rail gun is used by the United States Navy
and it is very unique in that it is a gun that does not use
gunpowder. Instead, it is powered by electricity and a magnetic
field. It has been a huge technological advancement because before
it was invented, the maximum range a gun could shoot a projectile
was 12 miles. A rail gun can reach a target 250 miles away in 6
minutes, traveling at a speed of around 16,000 meters per
second.
The Basic Parts of a Rail Gun
A rail gun uses large amounts of power, so a power source has to
be used that can generate millions of amps in order for a rail gun
to function. The armature is the most important part of the rail
gun because it is the metal piece (conductive sabot) that holds the
projectile. On either side of the armature, there are two
conductive rails which vary in length depending on the size and
power capabilities of the rail gun. The rails are connected to the
power source and the current from the source travels up one rail
(the positive rail) and through the armature and back down to the
power source through the other rail on the other side (the negative
rail).
Simulation of How a Rail Gun Works
How it WorksIn the parts of the rail gun where an electric
current is present, magnetic fields are present around rails. As
shown in the diagram above, the magnetic field rotates in a
counterclockwise direction around the positive rail. In the
negative rail, the magnetic field rotates in a clockwise
direction.The main reason that a rail gun works is because of the
third right hand rule. As illustrated in the diagram below, the
magnetic field is always pointing outwards towards the sky and the
current travels from the positive side to the negative side of the
power source, which is to the right. This means that the force of
the rail gun projects straight out of the gun. However, in order
for a rail gun to work effectively and travel long distances at
large speeds, there must be a great amount of force inflicted on
the projectile. This is why millions of amperes are required in the
power source for the rail gun to work properly.
Due to the fact that a rail gun requires millions of amperes,
the Navy does not have a solution for providing enough power to use
a rail gun on a naval ship yet. However, they are currently working
on building a type of battleship, the all-electric DD(X), which can
temporarily take some power from the engine whenthe rail gun needs
to be used. Not only can rail guns be used in the military, but
they can also be used to launch satellites or space shuttles into
outer space potentially because a rail gun can have multiple
projectiles, not just a missile.
Rail Gun BasicsA rail gun is basically a large electric circuit,
made up of three parts: a power source, a pair of parallel rails
and a moving armature. Let's look at each of these parts in more
detail.
For simulation (animation)
http://science.howstuffworks.com/rail-gun1.htmThe power supplyis
simply a source of electric current. Typically, the current used in
medium- to large-caliber rail guns is in the millions of amps.The
railsare lengths of conductive metal, such as copper. They can
range from four to 30 feet (9 meters) long.The armaturebridges the
gap between the rails. It can be a solid piece of conductive metal
or a conductivesabot-- a carrier that houses a dart or other
projectile. Some rail guns use aplasmaarmature. In this set-up a
thin metal foil is placed on the back of a non-conducting
projectile. When power flows through this foil it vaporizes and
becomes a plasma, which carries the current.Here's how the pieces
work together:An electric current runs from the positive terminal
of the power supply, up the positive rail, across the armature, and
down the negative rail back to the power supply.Current flowing in
any wire creates a magnetic field around it -- a region where a
magnetic force is felt. This force has both a magnitude and a
direction. In a rail gun, the two rails act like wires, with a
magnetic field circulating around each rail. The force lines of the
magnetic field run in a counterclockwise circle around the positive
rail and in a clockwise circle around the negative rail. The net
magnetic field between the rails is directed vertically.Like a
charged wire in an electric field, the projectile experiences a
force known as theLorentz force(after the Dutch physicist Hendrik
A. Lorentz). The Lorentz force is directed perpendicularly to the
magnetic field and to the direction of the current flowing across
the armature. You can see how this works in the diagram below.
Notice that the Lorentz force is parallel to the rails, acting
away from the power supply. The magnitude of the force is
determined by the equation F = (i)(L)(B), whereFis the net
force,iis the current,Lis the length of the rails andBis the
magnetic field. The force can be boosted by increasing either the
length of the rails or the amount of current.Because long rails
pose design challenges, most rail guns use strong currents -- on
the order of a million amps -- to generate tremendous force. The
projectile, under the influence of the Lorentz force, accelerates
to the end of the rails opposite the power supply and exits through
an aperture.The circuit is broken, which ends the flow of
current.
USURPING POWERRail guns require tremendous currents to fire
projectiles at speeds of Mach 5 or higher. This presents problems
for a traditional battleship because power cannot be diverted from
the ship's propulsion system. In the Navy's next-generation
battleship, the all-electric DD(X), producing this kind of current
will be possible. To launch a rail gun projectile, power would be
diverted from the ship's engine to the gun turret. The gun would be
fired, up to six rounds per minute, for as long as required. Then
power would be shifted back to the engine.
INTRODUCTION Railguns are a means of accelerating an object
based on an electromagnetic force. Such devices have been in use in
laboratory settings for several decades, but the number of
potential applications increases with advances in technology.
Although railguns are quite complex, their basic underlying
principles are simple enough for anyone with basic physics training
to understand. This design proposal will outline the principles
behind designing a low-velocity railgun for educational use in a
high school classroom.1.1 Railgun Theory The components of the most
basic railgun design include two parallel rails and a movable
armature, all of which must be electrically conductive. Current is
run down one rail, through the armature, and back up the other rail
to complete the circuit. A magnetic field is induced between the
rails by the current loop formed. A Dutch physicist named Hendrick
Antoon Lorentz formulated an equation for magnetic force, called
Lorentz force, by which the force on a current-carrying object by a
magnetic field is given by:
whereFis the force on the object,Iis the electrical current,is
the length vector of the current flow in the object, andis the
magnetic field. A simplistic railgun setup can be seen in Figure
1.
Figure 1 Simple Railgun Schematic [1] Accurately describing
railgun behavior is much more difficult than merely applying the
Lorentz force equation. As the armature travels down the rails, the
size of the current loop increases and thereby changes the
magnitude of the induced magnetic field. The position-time behavior
of the armature can therefore only be accurately described through
the use of multiple-order differential equations. A large amount of
current is required to produce a force large enough to accelerate
even a lightweight projectile. The force is largely dependant on
the electrical current because it is a product of the current
running through it and the magnetic field it experiences, which is
a function of that same current. The Biot-Savart Law describes the
induced magnetic field magnitude of a semi-infinite length wire
by
where0is the permeability of free space,Iis the current through
the wire, andris the radius of the wire [2]. It can be seen from
this law that, for a wire with a radius of ten millimeters, it
would take a current of 50,000 Amps to produce a magnetic field of
just 1 T at the wire surface! Even with parallel wires of this size
each contributing to a magnetic field four millimeters away from
the surface of both wires, 35,000 Amps would still be needed to
induce a magnetic field strength of 1 T. The force on the armature
is a function of the square of the current running through it.
Capacitors are often employed to produce the high current needed
because of their large charge storage and short discharge time.
Even in materials with minimal resistivity, a fraction of
electrical energy is lost in the form of heat due to impedance of
the conductor. Heat buildup can become significant at the large
electrical currents needed in a railgun. While a force on a
current-carrying object is the inherent mechanism behind the
railgun, it can also cause some problems. The same current that is
passed through the armature also flows through both rails, causing
a force on the rails that tries to push them apart. The rails are
subject to the same Lorentz force equation as the armature, so a
strong supporting structure is needed to contain the lateral
pressure on the rails and prevent them from flying apart. The
outward force on the rails, assuming the current in each rail is
the same because they are in the same loop, can be calculated
by
whereLis the length of the wire.1.2 Previously Constructed
Railguns Engineers have built railguns for recreation, research, or
real-world applications. Many military applications exist for the
high kinetic energy that a railgun can produce, but many hobbyists
have also created railguns out of sheer enjoyment. Railguns built
by others can help predict and prematurely correct some of the
problems that could be encountered in building such a device.1.2.1
Military Designs The military has been actively researching the
applications of railguns in military situations for several years
for a couple of reasons. First of all, railguns are capable of
firing projectiles with a huge amount of kinetic energy. Recent
tests at the University of Canberra in Australia [3] have produced
a force of 250,000 times that of gravity on a mass of 16 grams.
This translates to going from rest to 13,000 miles per hour in
under one-fifth of a second! Projected naval railguns from Batelle
will be able to fire up to six rounds per minute with an impact
speed of Mach 5, producing penetration up to forty feet [4].
Secondly, railguns require no chemicals to use. Rather than using
energy from controlled explosions like current weapons, railgun
ammunition will consist of electrical energy firing inert slugs.
This will almost eliminate the need for the military to store
dangerous explosives on ships and bases, increasing safety and
stealth. While railguns have not become standard issue as of yet,
they do hold promise in many exciting areas. Naval ships and land
bases will likely switch to railguns due to their large projected
ranges (up to 200 nautical miles) and lack of explosives to store
and protect [3]. The army is researching the possibility of using
railguns on armored vehicles because of their huge destructive
power and low armament storage needs. Launching supplies rather
than projectiles from a railgun is also being explored, and NASA is
even exploring this technique to launch supplies both from and
towards Earth.1.2.2 Amateur Designs Numerous amateur railguns have
been conceived and built for a variety of purposes. Some have built
these as recreational devices, others for the challenge of building
the railgun, and still others for demonstration purposes. Firing
speeds and armature properties differ for each gun and each
application. Some of the simplest railguns are for demonstration
purposes and can be built in a span of minutes. These simple
railguns, such as the one in Figure 2, simply use batteries or a DC
laboratory power supply to cause a small section of wire to roll.
These simple railguns demonstrate the principles of electromagnetic
motion, just as the more powerful ones, but for much less time and
money.
Figure 2 Simple Classroom Demonstration Railgun The majority of
amateurs build railguns that are capable of muzzle velocities
between 50 and 500 meters per second. Some have been for various
high school and college classes, while others have been built in
basements and garages as hobbies. One of the most well-known
amateur railguns was made by Sam Barros, a student at Michigan
Institute of Technology, and chronicled on www.powerlabs.org [1].
On his website, he outlines the theory behind railguns in general
and his design in particular, as well as providing insight on some
of the problems experienced in construction. Amazingly, many
amateurs are able to fire railguns at velocities large enough to
experience many of the problems of the larger military devices,
such as metal vapor arcing (MVA) and rail damage by electrical
arcing.1.2.3 Problems with Previous Railguns One of the most common
problems with railguns built in the past has been rapid rail
erosion. Erosion failure often occurs after only one or two uses in
some cases [5]. Rail erosion occurs much more quickly than would be
expected from purely frictional forces between the armature and
rails. The mechanism of rail erosion due to electrical current is
not fully understood and is under investigation. It is known that
highly polished surfaces with low coefficients of friction are
needed for maximum railgun efficiency. Another common problem is
the armature fusing itself to the rails upon firing. When a
stationary armature is fired by a railgun, it must overcome the
coefficient of static frictionin order to begin motion. The
coefficient of kinetic friction, which is much less than, is the
only barrier to motion after the armature is already moving. If the
armature is unable to overcome, the electric current energy put
through the armature will not be converted to mechanical energy.
This energy will instead transform into thermal energy, heating the
armature significantly. Enough thermal energy can cause the
armature to melt itself to the rails. Large contact surfaces and
materials with high electrical and thermal conductivity can help to
alleviate the melting problem. Some problems are a direct result of
higher muzzle velocities that are beyond the scope of this project.
The repulsion forces on the rails can cause the structural supports
to fail at high currents, as dictated by the Biot-Savart Law. At
very high velocities, a plasma can form between the rails by MVA.
This plasma can greatly reduce the lifetime of the rails, but it
can also act as an armature itself because it is highly
conductive.1.3 Detailed Objectives For this project, a railgun will
be designed and built for low velocities for use in high school
classroom demonstrations and physics/mechanics based experiments.
In order to remain safe for the client and all students involved,
the railgun must shoot lightweight projectiles at slow speeds.
Firing at low velocities with railguns poses its own unique
problems not often experienced by other rail gun builders. Too much
electrical power input will cause the projectile to accelerate too
much, but too little will cause the gun not to work at all.1.3.1
Criteria for SuccessBecause the railgun is to be used in laboratory
sessions, the gun will be designed to be educational and safe in
every possible way. Clear plastic will be used as a casing material
to allow visible inspection of the device at work. This device is
also to be durable so that the client may use the railgun year
after year in the laboratory. As such, much of the design will
revolve around making a sturdy, robust device that will erode very
little due to repeated use. Safety is the number one priority,
however. All electrical components must be completely insulated
from the outside world to prevent any electrical discharge into
anything other than the railgun components, and all structural
components must be sound enough to sustain even unexpected forces.
The maximum budget for the entire project, including material and
component costs, consultation fees, construction, testing, and
implementation, is $700 as set by the client. The project can be
considered a success if these objectives and goals are met in their
entirety.1.3.2 Classroom Uses The entire purpose of the design and
construction of this device is for demonstration of electromagnetic
principles to high school physics students. Most of the
electromagnetic theory behind railguns discussed in the theory
section could easily be discussed and demonstrated with a railgun,
including induced magnetic fields, electric current flow in
materials, and more. Most railgun behavior, such as muzzle
velocity, could be predicted through calculations and then verified
by experiments. The actual demonstrations and laboratory sessions
performed are to be decided by the client.