What they are?
Coil guns are an experimental electronic acceleration system. Still early in production the gun is showing much promise for the future of warfare, space and travel. Coil gun's can range from handheld to mile long, rocket accelerators. In each application the physics is the same.
How they work?
The coil guns work based around the principles of ferromagnetic projectiles and electromagnetic acceleration. By placing a ferromagnetic projectile within a series of coils, the object can be accelerated, on a large scale, out of our planet. The idea is simple. Magnets of opposite charges attract. By creating a series of magnets turning on, only briefly, an object can be accelerated forwards. Just like in the speaker experiment, running a current through a wire coil creates a magnetic field. If the ferromagnetic projectile is attracted to a coil and then the coil is shut off the projectile will be propelled through the coil, and if the next coil is turned on a just the right time the projectile will be attracted to that coil and accelerate towards it. The image below shows this occurring in real time. Hypothetically these coils could repeat the process infinitely, continuing to accelerate the projectile forward. However each coil does not double the speed of the projectile. Using K times the amount of coils only increase the speed by root K ex. doubling the number of coils allows for a 1.41 times increase in speed. In this way the
Found here: http://en.wikipedia.org/wiki/File:Coilgun_animation.gif
Flaws?
The guns have many flaws and, as they are still in their infancy, have not been fixed. Every shot fired requires charging time and this slows the rate of fire to nearly unusable. As we, as a society, expand and learn of new charging and storing options for electricity this problem will be overcome. Currently the military is investigating their application for soldiers. An issue with their use is that in the field the soldier is required to carry the power source, limiting their usefulness. In the future, as we learn of more efficient and lighter methods of storing energy and releasing the energy, the practicality of the gun increases dramatically.
Any future applications?
Leading military investigation has demonstrated the power of coil guns when attempting to launch a rocket into space.
An interesting video about the attempt at space launching through coils.
http://dsc.discovery.com/videos/discovery-project-earth-coil-gun-tech.html
As seen in the video, coil guns have a great potential to assist human kind as we expand our space operations. Another benefit by using coil gun based launches is that they cost approximately 10 million dollars as compared to the 450 million dollars currently spent on one launch. Also the coil guns are reusable and deteriorate very slowly. An issue still facing scientists is that the launching facility would have to be huge. Estimations are about a minimum of 1300 km long to approximately 2000 km long. At that distance the launch sequence would only take a mere 6 minutes and 12 seconds.
Source: http://www.instructables.com/answers/Could-a-coil-guns-projectile-escape-earths-gravi/
Question
If the projectile was leaving the muzzle of the coil gun at 10 m/s, and the same projectile left another gun with 36 coils at 20 m/s, how many coils were used in the first gun?
A:(Highlight for answer) 9 coils, by using the relationship of increasing the number of coils by K the speed is increased by root K. In this case the speed was doubled so that means the number of coils increased by 2 squared or 4. Thus 36/4=9.
External Links
An interesting link about a person who makes their own coil guns and writes about it. http://www.coilgun.info/mark5/home.htm
A great article about the physics behind the gun, it also goes in depth about the mechanical side. http://wiki.4hv.org/index.php/Coil_gun
A really cool handheld gun made from parts available to the average consumer. http://www.instructables.com/id/Coilgun-Handgun/
By Robin, Matt and Derek
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