is a liquid holding tiny magnetic particles that stay dispersed, and in a weak field its surface is almost smooth. As the field strengthens it grows orderly spikes. A liquid is not supposed to hold a shape. So what is going on there?
A competition one side wins past a threshold. Once the perpendicular field passes that threshold, and receives an extra pull, so it grows. Gravity and surface tension try to flatten it. The contest between them produces , and sometimes a fixed of spikes.
A magnetic liquid contains particles so small that thermal motion keeps them dispersed, so it stays a uniform liquid until a field is applied.
In a weak field its surface is almost smooth, because gravity and surface tension flatten it.
Above a certain threshold the balance flips. A small bump concentrates the field lines into itself and receives a stronger pull, so it grows further, exactly like the point that draws lightning.
The competition between the three forces produces the instability, and neighboring spikes repel one another into a hexagonal lattice. An orderly pattern appears by itself this way the moment an external force crosses a threshold. The shape of the spikes depends on the depth of the liquid, on its properties and on the shape of the field. A home video beside a magnet does not necessarily reproduce the research conditions.
wat. Ferrofluid spikes appear when the energy gained from the magnetic field exceeds the cost of lifting the liquid and stretching its surface.
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An orderly pattern can appear by itself the moment an external force crosses a threshold, a principle that recurs across physical systems.
How do we know?
The work compared a calculation of the shape of a single spike with experimental measurements above the magnetic threshold, and examined its response to a changing field too.
What is still unknown
The shape of the spikes depends on the depth of the liquid, on its properties and on the shape of the field. A home video beside a magnet does not necessarily reproduce the conditions of the research.
Learn something?
Where to next
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