Given the above:
You are to create a “blob” to roll (without sliding) down a long (>>1m) frictionless ramp using only gravity. The blob must fit inside a 12cm cube and weigh exactly 1kg. You are allowed to use any number of “real” materials (real = something you could buy at a retail store although you may have to transform it to your desired shape - just do this without resorting to magic or Star Trek technology). Give the materials, key material properties (e.g. density) and shape(s)/size(s) that would maximize the speed of the blob as it reaches the bottom of the ramp. Note: the blob must actually be able to roll, all parts at the same angular velocity, in case that’s not clear.