Have you often felt what a bother it was to use soap when a quick swish of your hands under plain water would do just as well? Most kids prefer it that way. But while water alone may remove some of the dirt from the surface of your skin, soap added to the water does get you cleaner.
If you looked at a cross-section of your skin under a microscope, you would see that it has many hollow areas, or valleys, where particles of grease and dirt can become embedded. Water alone may get under the dirt and push some of it out, but when that water hits grease, it will simply sit on top of it in a bubble or just roll off.
But add soap to that very same water and you have a completely different action. The action of mixing soap into water pumps air into the water and forces it to spread out as it creates bubbles. A bubble is actually a balloon of air with a thin outer covering of soap and water.
While bubbles seem to be very delicate and weak things, they actually work like dozens of strong magnets. Just as magnets pull tacks towards them, soap bubbles-pick up dirt and pull it away from the skin. Then the dirty bubbles are carried away in the rinse water, leaving your skin clean.