# What is a force multipole?

In a recent talk about physics and mechanics inside the cell, I heard such terms as 'force monopole' and 'force dipole'. What do such terms mean?

Are they talking about the angular distributions, viz. the $\ell=0,1,...$ modes of the spherical harmonics? If so, then what would a force monopole, dipole, etc. look like?

Any references on this topic? A simple search did not turn up anything.

• I would assume they mean the decomposition of the force field into vector spherical harmonics. The force monopole is the constant part, the force dipole would tend to stretch or compress along an axis, and so on. – knzhou Apr 17 '18 at 16:10
• That sounds close to what they were implying. I read the Wikipedia article, but could you please elucidate more the physical significance of each term? Perhaps with examples. Also, do you have any references? – ap21 Apr 19 '18 at 17:32