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Registered Member #289
Joined: Mon Mar 06 2006, 10:45AM
Location: Conroe, TX
Posts: 154
no, the same impulse, recoil is momentum, not energy,
Dr. Slack, that momentum you speak of was created by imparting a force on the projectile, a force created by the energy stored in the cap bank. Therefore I think it's acceptable to use the term energy, but really, why be so picky about semantics, my comment was clear.
ahh!, perhaps that's your problem. There *is* a "stop" attached to, if not behind the rails. You have to get the current into and out of the rails, through a wire and a switch, from your power supply. They all experience forces too.
Yes, we all know the connecting wires will experience a force, that is why I said:
but some of it is wasted pushing cables and G-10 around as well
no. The force due to a current in a magnetic field acts at right angles to the current. So the force acts sideways to, not along the rail. The rails try to fly apart, but there is no force in a direction that could be called recoil.
Ah, I said almost exactly that, and you quoted it. Seriously, the "repulsive force pushes the rails against the mounting structure" is the same as saying "force acts sideways to, not along the rail" Ya, sideways, as in against the mounting structure...
Instead, the repulsive force between the two (which is also acting on the projectile) pushes them up against the mounting structure with more than enough force to hold them there
Is it worth repeating? There is no recoil force on the rails.
Fortunately I never said this, that was the point of me mentioning that the rails will stay in place without a back stop.
I think you may be over analyzing my post a bit, we said basically the same thing. Regardless, this thread has lost all useful value, moving on...
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
HVguy, I am truly in awe of your rhetoric, your obfuscation, your need to be right, and your tenacity. A glittering career is yours for the taking should you decide to go into patent or criminal advocacy, or politics.
However, before I leave this thread, I ask you to do a few simple calculations. A gun (rail, spud, Smith & Wesson, it matters not) is mounted on a frictionless track so that it is totally free to recoil weighs 1kg, and fires a 10g projectile at 100m/s. Compute the recoil velocity of the gun, and the momentum (mv) and the energy (0.5mv^2) of both the projectile and the gun after firing. Do the same calculations where the gun now weighs 10kg, all other parameters staying the same.
Do you notice anything about the momentum calculations? Do you notice anything about the energy calculations? Is there a difference? Is one more appropriate to use than the other for recoil calculations? Is the difference between momentum and energy just being picky?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Dr. Slack wrote ...
HVguy, I am truly in awe of your rhetoric, your obfuscation, your need to be right, and your tenacity. A glittering career is yours for the taking should you decide to go into patent or criminal advocacy, or politics.
All of which pay better than engineering, oddly enough.
(could there be a moral here about the values to society of absolute truth vs. relative truth?)
Registered Member #567
Joined: Tue Mar 06 2007, 10:55AM
Location: Singapore
Posts: 147
Wow, this thread blew up a bit.
Anyway, so is it as simple as this?
When you pass a current through a loop of wire, the loop will try to expand. The forces add up to cancel each other out. Now, just so happens that only one section of the loop is free to move, and it accelerates away. All the laws of physics are satisfied. Rearrange a bit, and we have a railgun. Yes?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Yes. You can think of magnetic pressure inside the loop trying to expand it, like compressed air in a balloon. The Lorentz forces are about uniform per unit conductor length, and about normal to the direction of current, so the analogy with pressure seems reasonable to me.
What part of an air gun or spudgun does the recoil get imparted on? It's the same question, just with air pressure instead of magnetic pressure. Klugesmith thought it was the breech, and that seems reasonable. But what about an air cannon with a large reservoir feeding a smaller diameter barrel? Similar situation to the railgun with its wiring at the breech end.
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Railgun recoil
