Soap

1. There are two reasons why water doesn't clean well by itself. Both of these reasons have to do with water's high polarity.
   1. The strong surface tension of water prevents it from getting into small spaces.
   2. Most dirt is non-polar so it doesn't dissolve well in polar water.
2. Sodium stearate is a common soap which solves both of the problems described above. Notice that one end is polar and the other end is non-polar. This make sodium stearate a kind of schizophrenic molecule. It can dissolve in both polar and non-polar substances.
3. To see how this breaks up water's surface tension: Breaking up Surface Tension.
4. When soaps are dissolved in water the molecules arrange themselves into groups called micels. The non-polar ends will congregate together while the polar ends will interact with the water. Because dirt is mostly non-polar the dirt gets dissolved into the center of the micelle.