One activity is when sugar is dissolved in a cup of coffee. If one drops a sugar cube(solid)into coffee(liquid), the molecules of sugar will travel from high concentration(in the cube) to low concentration, throughout the cup of coffee until they are equally distributed. You don't even need to stir the sugar and it will still diffuse. Diffusion is a type of passive transport that requires no additional energy for the process to occur. Another example is adding kool-aid mix into water. The kool-aid will slowly diffuse into the water from a region of high concentration, to a region of lower concentration. If one drops dye into a bucket of water, the molecules of dye will diffuse until the water has a uniform color throughout. These are some examples of diffusion that occurs with a solid into a liquid.