Here is a question posed to me recently that I'd like to post for discussion. It has elements of biology and physics. A butter knife does a poor job of cutting through a tomato or your hand, whereas a razor sharp knife cuts through quite easily. Why is this so? What mechanism is at work at the microscopic or molecular level? As the thickness of a blade becomes narrower, does it reach some critical dimension allowing it to separate the bonds of molecules along the cutting plane? Some thoughts; as you move though a cross-section of any tissue, there are non-uniform cohesive and adhesive forces holding it together. I am thinking these forces are related to the bond-energies holding the molecules together. The case of the butter knife might be easier to think about. The tip edge is "relatively" wide or blunt. As you cut, the surface is pressing over a wider area and pushes against cells or groups of cells. If you push hard enough, it will cut though tissue, but not very evenly, across the cutting plane.. Perhaps the downward force of a butterknife tears the tissue, with the weakest molecular bonds pulling apart initially and then successively stronger bonds breaking, until the tissue separates completely. So what is the mechanism that allows a sharp blade to easily cut though biological tissue?