Molecular machine part3

 The other day, I explained a mechanism of molecular machine, chemical affinity. Here, I would like to state the second mechanism, steric obstacle. 
 Molecules have some electrons, so each molecule has repulsion when each is positioned nearly. Therefore, when molecules are constructed assembly, the steric obstacle try to minimize and locate in proper structure. Chemists take advantage of this mechanism and construct supramolecules which have unidirectional motion. 
 Thank you for my poor sentence. Goodbye.