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A rail gun is a weapon that uses a magnetic field to fire projectiles instead of the traditional gun powder magazine. This technology is the first electronically powered weapon system ever proposed. If the term rail gun seems familiar to you, you probably remember seeing it in action in the recent Movie Transformers 2: Rise of the Fallen. You may have noticed that the gun had a very large firing range since it could be fired from the Red Sea and still hit a target on one of the Giza Pyramids. This is just a demonstration of many of the advantages of a rail gun over traditional firearms.
As mentioned before a rail gun works by using a magnetic field to propel a projectile, in this case a bullet, at phenomenal speeds. This principal works using the Lorentz force. Essentially, the Lorentz force states that electrical current is parallel to a magnetic field. A electric force produces a perpendicular magnetic force.
The structure of a rail gun is quite simple. First there is the power supply. Preferably the power source produces an alternating current. The next part are the rails. The rails are conductive with one side being positive and the other being negative. Last of all is the projectile itself. It has a bar called an armature which will connect the projectile to both sides of the rails so that current can be conducted. The current then creates the magnetic field that will fire the projectile.
A rail gun has many advantages as well as draw backs. First, there is the speed. A rail gun can fire projectile at speeds exceeding 3500 meters per second. This also means a lot for range a rail gun bullet fired at such velocities could hit a target from 250 miles away in 6 minutes. Current Navy cannons which are believed to have the longest firing range only have a reach of 12 miles. However the velocity of the projectile is only limited by the atmosphere and how much electrical energy is used. In some test projectiles have even been fired at speeds over 4000 meters per second.
This speed, power, and accuracy seem to make the rail gun a definite possibility for future weapons systems. However, it still has some flaws. First is resistance. Whenever pass a current through a medium it will naturally heat up due to some natural resistance to the current. The other problem is that the repulsing force of the magnetic field goes both ways so over time it can also damage the rails over time. Finally there is the size issue for the power supply. It takes a lot of energy to fire rail guns so the power source also needs to be large. This limits the applicability of rail guns as portable weapons.
If you enjoyed this article there are several others on Universe Today that you will find enjoyable. There is a great article on how long it would take to travel to the nearest star. There is also an article on how to save the world from an asteroid impact.
You can also look at articles and other resources online. There is a great article on rail on guns on the how stuff works website. There is also a great article about rail guns on the popular mechanics web site.
You can also check out Astronomy Cast. Episode 42 talks about magnetism.