The Liquid Drop model was the first formula designed to compute the binding energies of nuclei as a function of the number of protons (Z), neutrons (N) and total number of nucleons (A). It treats the nucleus as a drop of fluid of very high density that can't be compressed, held together by the nuclear force (a residual effect of the strong force). While a crude model, the liquid-drop model accounts for the spherical shape of most nuclei and makes a rough prediction of binding energy.

The equation looks quite complicated as it has five terms:

Semi-Empircal Mass Formula

Each of the five terms has a numerical coefficient in front: aV, aS, aC, aA, and aP.

By working through the activities that follow, you will be able explore the different coefficients, see some of the uses of the formula, and use it to predict the size of neutron stars.