You're only considering mechanical forces. You're right about the direction of friction (forces the gun forward rather than backward), though if these forces are of the order that I'm imagining, then it would appear as recoil when the setup returned to equilibrium. In essence, for a railgun with any sort of efficiency, the friction would have to be very low, so there should be very little 'recoil' in either direction.Originally posted by: FrankSchwab
Originally posted by: CycloWizard
Thus, this interaction of forces will not result in mechanical force (i.e. recoil) being imparted on the gun itself except due to friction at the contacts.
And grant2 was trying to explain that you are wrong.
In your world, the gun would attempt to follow the projectile, because friction on the contacts will cause a force on the gun in the direction of travel of the projectile (it tries to drag it along). This has all kinds of interesting ramifications that are, umm, "not supported by experimental evidence".
/frank
Originally posted by: CycloWizard
I was trying to explain that there are more than only mechanical forces. There are mechanical forces (the kind that you can easily see and understand) and electrical forces that are not really visible or tangible. As I said, the mechanical force imparted on the projectile counteracts the electromotive force. Thus, this interaction of forces will not result in mechanical force (i.e. recoil) being imparted on the gun itself except due to friction at the contacts.Originally posted by: grant2
I don't like it either.
If you accelerate an object, using ANY force (mechanical, electrical, gravitational, magnetic), then an equal & opposite force must be applied to some other object(s).
In the case of a projectile launcher, there are 2 practical possibilities for what that opposite force is applied to: propellant, or the launching mechanism. Since a rail gun does not use propellants, the mechanism must receive the force. This is what I believe is called recoil.
At least that's my very basic understanding of physics.
Wrong. I'm not talking about magic, I'm talking about magnetism. By your logic, gravity doesn't exist.Originally posted by: RelaxTheMind
Force is force if you are trying to bend the lawas of physics good luck. If an object is being pushed one way with any type of force the object is pushing back equal and oppisite force. the mechanism is the propellant in this case. If you want o move an object without any type of propellant you may be talking about magic. Relative to the propellant the mechanism is actually moving backwards. Other factors would be air (yes air has friction), gravity trying to pull it to the bottom of the mechanism the "forces" holding the propellant in the mechanism.
Put it this way to put it in better perspective. If you raise the weight of the projectile (say twice the weight of the mechanism) the tendency of the mechanism to push itself backwards "recoil".
there really wouldnt have to be a propellant but would need to be there to make it worth while. The idea of a rail gun is an object getting propelled and accelerated along the rail. a bullet being shot into a tube at 400m/s thats going to accerate it to say 800m/s
agrrements/disagreements?
Basically, magnetism exerts a body force (similar to gravity - no contact required) on the projectile. Since there is no contact between the projectile and the barrel, the projectile exerts no reactive force on the barrel itself.
I didn't know asshats would bother coming into this forum. If you want to tell me I'm wrong, you could do it nicely. Why be an ass? Case of penis envy?Originally posted by: FrankSchwab
CycloWizard - your ignorance is daunting.
Basically, magnetism exerts a body force (similar to gravity - no contact required) on the projectile. Since there is no contact between the projectile and the barrel, the projectile exerts no reactive force on the barrel itself.
Might want to do a search for roller coasters. I know several of the newest, biggest, fastest use similar technology for their initial launch.Originally posted by: bobsmith1492
Whoa now.... I'm just trying to ask a simple question here
By the way, a rail gun firing will exert force on both the bullet and an equal and opposite force on the launcher. I see no arguments; this is basic physics and no one has said otherwise.
So anyway, how does an electromagnet exert force on a nonmagnetic ferrous material? I'm looking for equations. So far, I know the force due to a current i through a wire of length l in a field of strength b is given by F = i lxb where x is crossing vectors l and b where vector l has the magnitude of the length l and direction of current i. The unknown is the field b which would be exerted by the ferrous material in question; I heard something about induced charges/induced currents which I suppose would create a magnetic field. Anyone know about induced currents and (mathematically) how they are formed in a solid object (cylinder) ?
bob, there's your problem, you've got to use winebottles for your leiden jars!probably something to do with the power supply and my crappy saltwater capacitors (Jones' Soda)
The equation I posted doesn't include induced current. It's the current in the rails rather than in the projectile. Got it here.Originally posted by: skene
Figuring out the induced current on the projectile isn't just one simple equation. The changing electric field through the wire, ie turning the current on and off, creates the magnetic field. The creating and destroying of the magnetic field creates the induced current in the cylinder.
Honestly, the best thing is to go to a university or possibly high school library and check out some electricity and magnatisim books if you want get into the nitty gritty bits. Another great place to find info is http://scienceworld.wolfram.com/physics/ Check out the mangnetic field section in electromagnatisim. That site has TONS of info on it, and unless you've got a decent knowlege base to begin with it might be overwhelming. There really is no replacement for a good text book or teacher explaining theory.
Just out of curiosity, you say you just started magnatisim in class, are you in high school, college, what? In high school I thought of making a rail gun, but figured out a tesla coil was much easier, made just as much noise, and still scared half the judges in the science fair without shooting things at them. Just be VERY CAREFUL when playing with that much power. Once you get shocked by a car battery you'll learn that quickly...better to do that then with a microwave transformer.
edit: fixed a garbled sentence
Originally posted by: CycloWizard
I didn't know asshats would bother coming into this forum. If you want to tell me I'm wrong, you could do it nicely. Why be an ass? Case of penis envy?
Since there is no contact between the projectile and the barrel, the projectile exerts no reactive force on the barrel itself. For this particular system, there is some small friction between the projectile and the barrel, so this will impart some recoil, though how much depends heavily on the specifics of the system. Ideally, you would impart all of the electrical energy on the projectile as kinetic energy and there would be no recoil. Obviously this isn't the case in reality.
Thus, this interaction of forces will not result in mechanical force (i.e. recoil) being imparted on the gun itself except due to friction at the contacts.
In essence, for a railgun with any sort of efficiency, the friction would have to be very low, so there should be very little 'recoil' in either direction.
I have no idea how to reconcile this recognition of reality with your statements above. The truth of the matter is that every newton of force imparted to the projectile will also be imparted to the barrel or rail, directed in the opposite direction. This is recoil, and will exist in any scenario you can imagine, real-world or the frictionless world of freshman physics. I'm hoping that we can agree on this.The repulsion force would grow the closer the magnets become, so if someone pushed down on the top magnet, the downard force on the magnet I am holding would increase accordingly.
Originally posted by: CycloWizard
I was trying to explain that there are more than only mechanical forces. There are mechanical forces (the kind that you can easily see and understand) and electrical forces that are not really visible or tangible. As I said, the mechanical force imparted on the projectile counteracts the electromotive force. Thus, this interaction of forces will not result in mechanical force (i.e. recoil) being imparted on the gun itself except due to friction at the contacts.