Although this investigation refers to physical processes, it actually deals with only one process, diffusion . Diffusion is caused by kinetic energy , the energy of motion.
Temperature is a measure of kinetic energy.
Molecular movement due to kinetic energy is random. Molecular weight - Smaller molecules move faster than larger molecules. State of matter - Solid, liquid, gas. Molecules move fastest in a gaseous environment and slowest in a solid environment. You will be looking at all four properties during this investigation to determine the cause of diffusion.