Explain propene

In propene, the H₃C-C bond dipole adds vectorially to the smaller H-C bond dipole; the resultant is smaller than the H₃C-C bond dipole itself, as the following diagram shows. In 2-methylpropene, the resultant of the two H₃C-C bond dipoles is about equal in magnitude to one H₃C-C bond dipole. (This can be shown analytically if we suppose 120° bond angles.) 2-Methylpropene has a somewhat greater dipole moment. (In the following vector analysis, the H-C bond dipoles of the CH₂ groups are ignored due to they cancel in the comparison of the two molecules.)