By the KSS bound, the ratio of eta to entropy density of these substances is lower bounded by one over 4pi. (10[1])The stress-energy tensor of an ideal one of these substances is rho plus p (10[1])times (-5[1])a product of 4-velocities plus p times (-5[1])the metric tensor. In the rest (10[1])frame, a “perfect” one of these substances (-5[1])is parametrized by its isotropic pressure and energy (-5[1])density, (10[1])and therefore has a diagonal stress-energy (10[1])tensor. (10[1]-5[1])By definition, these substances have zero shear modulus, (10[1])meaning they cannot undergo shear stress (10[1])without (10[1])deformation. (10[5]-5[3])Many (-5[1])Bose–Einstein (-5[1])condensates act like an idealized (10[6]-5[1])“super” one (10[1])of these (10[2]-5[1])substances (10[14]-5[2])that (-5[1])move (10[3])without dissipating (10[1])energy. (10[6])The Navier–Stokes (10[2]-5[1])equations (10[4])are central (10[4])equations (10[1])in the “mechanics” (10[4])of, (10[1]-5[1])for 10 points, (10[3])what substances that can flow, (10[1])including (10[1])liquids (10[1])and gases? (10[1])■END■ (10[10])