is Principle Conservation of Momentum applied to 2-dimensional and 3-dimensional collisions? and y is it so?
Momentum is conserved in all three dimensions individually. That is, the "x" component of momentum is conserved independently of the "y" and "z" components. Why? Because space is isotropic - it seems to have no "preferred" directions in which physical properties change. Do any experiment, then rotate your apparatus to a new orientation and repeat. You'll get the same results.
It also follows that the total momentum vector is conserved, because it's just the sum of the components.
James, isn't spacetime a continuum? To rotate your experiment into a new orientation doesn't split spacetime into single dimensions. Length, width, and depth are human concepts defining and creating coordinates in spacetime for us but they are not really divisible experimenting. Isn't that statement mixing theory and reality? If in one object that what you defined as being width, extends past that what you referred to as length, won't you then have to change definition for those two? Like spilling out some water for example and measuring the changes in length etc.
