Eli5, How does a railgun work?
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It uses the lorentz force, when there is a magnetic field and an object that has current flowing through it perpendicular to the field this will generate a force perpendicular to both the magnetic field and the current direction.
In a railgun the projectile is usually part of a closed circuit, this means there is current going trough it, and because the circuit acts as a coil there is a magnetic field as well, so the lorentz force created from this propels the projectile.
Take a piece of heavy sharp metal. Generate extremely strong magnetic fields around it aligned in the same direction. Magnetic fields accelerate the projectile. Really, really, really fast.
Upside, you don’t have to deal with the pressures generated by using burning energetic materials to push the projectile.
Downside, you need a lot of energy and materials that handle it.
Essentially, you have two conductive rails with a lot of capacitors connected and then you short circuit the the whole thing with a projectile between the rails. The extremely high current through the rails and the projectile create a strong magnetic field that accelerates the projectile forward along the rails.
Have you ever seen a baseball pitching machine? The kind with the rotating wheels that sling out fastballs at a batting cage? Imagine a bunch of those laid end to end with the baseball passing through each one. Now swap out the rotating wheels for electromagnetism and the baseball for a conductive projectile and that’s basically a railgun (without getting too much in the weeds about the Lorentz force and right hand rules).
Putting current through a loop of conductive material tries to push the loop apart. Putting a lot of current pushes a lot, and making all parts of the loop but one very sturdy and bolted down results in the non-sturdy part being pushed out fast. Aim that part at something and you got a railgun.
There are issues with this. The first one is you need a hell of a lot of current to push a projectile to speed that rival conventional guns, which is not something batteries or even generators can provide: you get around this by storing the energy in massive capacitors that can then release it fast. The second one is that the current heats up the loop, in our case the rails and the projectile, and makes them expand. Precise fits are not precise anymore, things grind together and everything heats up even more, resulting in horrendous barrel life (in the order of a few shots instead of several thousands): last I checked this was the main issue the US Navy had with their massive railgun prototype.
Two conductive rails sit parallel to each other.
Between them, a conductive projectile is touching both rails.
We pass a very powerful electric current from one rail to the other, through the projectile. This creates a strong electric field and (as always happens when you make an electric field), this generates a perpendicular magnetic field.
Since the projectile has just become very magnetic (it has an electric current running through it, which makes it magnetic), this magnetic field pushes on the projectile, which will slide along the rails and keep getting pushed as long as there is electricity flowing through it.
This can make the projectile go really fast, and the more electric current you put in, the faster it goes.
There is a problem though, and we don’t know yet how to solve it.
The rails touch the projectile, pass a ton electrical current to it, and the projectile slides along them really fast. That burns the rails really badly with heat and friction, destroying them quickly.
If the projectile just barely doesn’t touch them, there’s no friction, but instead the electricity jumps a tiny distance (called an arc).
We use arcs to weld metal, because of how good ab arc is at melting or cutting metals.
This also destroys the rails, really fast.
We can protect them will a layer of graphite, which is conductive and slick, but it only helps a little.
We’ve tried lots of good ideas for solving this problem but none of them have really worked.
Railguns are cool, but really expensive and they eat themselves really fast.
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