 This change in both the pH and electrochemical potential gradient between the inside of the cell and the outside produces a proton motive force, as the protons will want to naturally flow back into the area of low concentration and with a voltage closer to zero from their current situation of being in an area of high concentration of positively charged protons.The reasons for this are twofold.For one, substances in nature have a tendency to move from areas of high concentration to areas of low concentration, as is evident by dropping a drop of food coloring in a glass of water.