Can someone explain the physics around railguns.
Do they use Electromagnetic waves for propulsion or?
In: 1
The electric force and magnetic force are both parts of the electromagnetic force (one of the 4 fundamental forces). You can’t have electricity without magnetism and vice versa.
When an electric charge moves, it creates a magnetic field, and in order to have a magnetic field, you need charges to move.
When current moves through a wire, it creates a magnetic field that loops around the wire. This follows whats known as the eoght hand rule. Take your right hand, if you put your thumb in the direction of the current, your fingers loop around the wire in the direction of your fingers.
The idea with a rail gun is if we have a magnetic field going through a projectile, we can run current through that projectile, and the magnetic field produced by that current will interact with the other magnetic field and we get a magnetic repulsion.
The formula is F = IL×B. The force is equal to the current, times the length of wire (width of the projectile in this case) cross product (vector mathematics you don’t need to understand) with the magnetic field.
The direction of the force is also determined the the right hand rule, if you point your thumb in the direction of the current, and have your fingers extend in the direction of the magnetic field, your palm points in the direction of the force.
The cross product is a way to multiply vectors and its at its maximum when the two vectors are perpendicular to each other, and 0 when the vectors are parallel. Most of the time you can replace it with sin(θ) where θ is the angle between the two vectors.
Let’s say we have a rain gun it produced a magnetic field of 1000T, launches a projectile of 1cm wide, with a current of 1A. And let’s say the barrel is 1m long and projectile is 1kg.
Assuming the magnetic field is perpendicular to the current (which makes the most sense because it would be the most efficient) the force will be F = 1A * 10^-2 m * 10^3 T = 10N
The projectile will be launched with a energy of W = F•d = 10N * 1m = 10J
That will be a velocity of v = sqrt(2 KE/m) = sqrt(2 * 10J/1kg) = 4.47 m/s
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