1. A system for creating physical simulations using hand-sketched three-dimensional (3D) objects, comprising: an electronic sketching device; a memory device for storing a program; and a processor in communication with the memory device, the processor operative with the program to enable: 3D objects to be hand-sketched and assigned physical descriptions; and behavior of the physical descriptions to be simulated in a physics environment, wherein more than one 3D object is hand-sketched and simulated at a time and strokes of one of the hand-sketched 3D objects are interpreted as being separate from strokes of another of the hand-sketched 3D objects when they overlap as they are being made on the electronic sketching device by modeling the hand-sketched 3D objects different from each other as they are input, wherein a first 3D object is assigned surface parameters including at least one surface friction parameter as it is sketched and a second 3D object is assigned surface parameters including at least one surface friction parameter as it is sketched, and the surface friction parameters determine how the first and second 3D objects actively move after they collide with each other.