Magnetic tension force

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The magnetic tension force is a tension that exists along magnetic field lines. It is due to the existence of magnetic pressure and the linear nature of the magnetic field. The magnetic field contains an energy density per unit volume; this takes the form of a pressure transverse to the field, because compressing field lines close to one another is equivalent to strengthening the magnetic field. However, shortening a field line reduces the total volume of space occupied by strong magnetic field, without changing the field strength in the rest of the field. Interplay between magnetic tension and magnetic pressure is responsible for the shape of magnetic field lines in the absence of constraining forces.

Magnetic tension is particularly important in plasma physics and magnetohydrodynamics, where it controls dynamics of some systems and the shape of magnetized structures.