What is the similarity between simple diffusion and facilitated diffusion?

they are both types of passive transport which means they require no energy. They both work with the concentration gradient which means they go from a high concentration area to a low concentration area. The differences are simple diffusion just goes though the membrane of a cell while facilitated diffusion uses a protein channel

Simple diffusion: it is the process where molecules move from a area of high concentration to an are of lower concentration. There is no energy needed in simple diffusion. For example when sodium is highly concentration in a cell, it moves outside of the cell where sodium is less concentration. it takes no energy as simple diffusion is random and molecules move according to their concentration.