A naive first model of a star is a static (i.e. non-rotating) spherical (compressible) ball of gas of density (r). The gravitational force is balanced by the pressure P. (a) Write down Euler's equation in this situation by setting v = 0 . Note: This is a totally unrealistic model of a star; stars are usually rotating. Hint: The gravitational potential satisfies Newton's law 2 = 4G. (b) Show that the equation of continuity is satisfied (trivially)