Round 9: Tossup 7

By the KSS bound, the ratio of eta to entropy density of these substances is lower bounded by one over 4pi. The stress-energy tensor of an ideal one of these substances is rho plus p times a product of 4-velocities plus p times the metric tensor. In the rest frame, a “perfect” one of these substances (-5[1])is parametrized by its isotropic pressure and energy density, and therefore has a diagonal stress-energy (10[1])tensor. By definition, these substances have zero shear modulus, meaning they cannot undergo shear stress without deformation. Many Bose–Einstein condensates act like an idealized (10[1])“super” one (10[1])of these substances (10[1])that move (10[2])without dissipating energy. (10[1])The Navier–Stokes (10[1])equations are central equations in the “mechanics” (10[1])of, (10[1])for 10 points, (10[1])what substances that can flow, including liquids and gases? ■END■ (10[1])

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