5.16 Superfluids

5.16 Superfluids

Superfluidity is the characteristic property of fluids with zero viscosity i.e., flow is frictionless. A substance exhibiting this property is a superfluid. Superfluids flow without loss of kinetic energy. They can flow through incredibly narrow spaces without any friction.

Superfluidity is achieved in some substances at extremely low temperature. For example, in fluid dynamics, a vortex is region in a fluid in which the flow revolves around an axial line, which may be straight or curved. The vortices are generally created at a moving boundary due to frictionless conditions. Vortices move with the fluid and dispersed by the action of viscosity.

Superfluid helium-4 is the most studied example of superfluidity. It changes from a liquid to a superfluid just a few degrees below its boiling point of $-452^{\circ}\mathrm{F}$ ($-269^{\circ}\mathrm{C}$ or $4\,\mathrm{K}$). Superfluid helium-4 moving as a normal clear liquid, but it has no viscosity. This means that once it starts to flow, it keeps moving past any obstacles.

Tidbits:

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• Parachutes increase air resistance (drag) by creating a large surface area, which counteracts the force of gravity. This slows down the person's fall, allowing them to land safely.
• Superfluids can "climb" up walls and over edges of containers because they do not experience friction like normal fluids do.