Subject: What is a simple exp. for measuring the diffusion of molecules in water?

I am in the sixth grade and need to design a simple experiment to observe 
the diffusion of molecules in water for my science fair project.  I can't 
think of an experiment that will help me understand how molecules diffuse 
through the mater.  I've thought of using food coloring and jars of water 
at various temperatures to determine if the temperature of the water 
affects how fast the molecules diffuse through the water.  My teacher says 
I need to find out if the molecules are moving through the water by 
diffusion or osmosis or by some other method?

Re: What is a simple exp. for measuring the diffusion of molecules in water?