Practical Coilgun Design 

Magnetic Materials

Force  Where Does It Come From?Okay, so you have some iron in a magnetic field. So what? Where does the force come from? When you hold two magnets and bring them together, you can feel the force but not see it. So it seems mysterious, but it must have something in common the more familiar forces, right? This page briefly summarizes the physics of forces, along with some math that I can't explain. For a serious understanding you'll need to pursue a college physics course or textbook. Force Is the Gradient of Potential EnergyForce is the gradient of potential energy. This is true for anything: gravity, electric fields, mechanical force, springs and rubber bands, air pressure, magnetism. Anything you can think of! The gradient operator tells how a function varies in different directions. It is a vector given by these two rules:
In short, the gradient tells you how to calculate directional derivatives. If a system has a potential energy field, then it invariably generates forces. "Potential energy" is defined by the stored energy as a result of an object's position. Force In a Magnetic FieldThe potential energy in a magnetic field is Recall that , i.e. magnetic induction vector B is equal to permeability µ multiplied by magnetic field vector H. Therefore the energy density in a magnetic field is Note that force units depend on your choice of systems:
Although the equations look similar, these are fundamentally different units. They are not basically comparable since they have different dimensions. 



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