A few years ago I challenged my class to use the method of volumes by slicing to compute the volume of a 4 ball, knowing the volume of a 3-ball. This leads to a slightly challenging trig integral, but not out of reach for a strong calculus student. (no one did it however.) This Fall while teaching the concept of work, I noticed the work integral for pumping liquid from a tank, is just the "cylindrical shells" integral for 4 dimensional volume (except for the factor of 2 pi). So if they have computed the relatively easy integral of work to empty a unit radius hemispherical tank of unit density liquid as pi/4, it follows that the volume of a 4 ball of radius a, is (2pi)(pi/4)a^4 = (pi)^2 (a^4)/2. Is this a standard observation?