- #1
abilolado
- 23
- 7
Hello all.
Me and some friends are building a coil cannon, and we've been doing some calculations [I know its unecessary but... well, we're physicists! (well, physics students...)]. But we got stuck.
How to calculate the force acting on a steel bar (or some other ferromagnetic material, maybe there's a constant related to each type of material for this application) of length [itex]L_{bar}[/itex] and radius [itex]R_{bar}[/itex] inside a solenoid of [itex]N[/itex] turns with current [itex]i[/itex] flowing through it ([itex]R_{bar}<R_{solenoid}[/itex])?
I found approximations that the magnetic field inside the solenoid is [itex]B=\mu N i[/itex] (using the right hand rule to find the direction, no problem there). I don't know, however, how to get the force applied on a steel bar under this field. Even an approximation would be great (But exact solutions are very appreciated, even more if they have the whole process of deriving the equation, hehe).
From the demonstrations online, I see that the bar oscillates going in and out of the coil. So I'm guessing there's some sort of harmonic oscillation approximation.
Much like shown in this clip (2:13):
(Unless the damping comes from something other then friction, there's no need to include it)
PS: Since we're using a capacitor bank, the current will not be constant, but I guess I can integrate the approximation over a varying current anyway.
Me and some friends are building a coil cannon, and we've been doing some calculations [I know its unecessary but... well, we're physicists! (well, physics students...)]. But we got stuck.
How to calculate the force acting on a steel bar (or some other ferromagnetic material, maybe there's a constant related to each type of material for this application) of length [itex]L_{bar}[/itex] and radius [itex]R_{bar}[/itex] inside a solenoid of [itex]N[/itex] turns with current [itex]i[/itex] flowing through it ([itex]R_{bar}<R_{solenoid}[/itex])?
I found approximations that the magnetic field inside the solenoid is [itex]B=\mu N i[/itex] (using the right hand rule to find the direction, no problem there). I don't know, however, how to get the force applied on a steel bar under this field. Even an approximation would be great (But exact solutions are very appreciated, even more if they have the whole process of deriving the equation, hehe).
From the demonstrations online, I see that the bar oscillates going in and out of the coil. So I'm guessing there's some sort of harmonic oscillation approximation.
Much like shown in this clip (2:13):
(Unless the damping comes from something other then friction, there's no need to include it)
PS: Since we're using a capacitor bank, the current will not be constant, but I guess I can integrate the approximation over a varying current anyway.