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Inelastic neutron scattering resolves $E_i-E_f\ne 0$. Through conservation of energy, a peak at positive $\hslash \omega$ identifies an allowed excitation energy; through momentum conservation, its location in $\mathbf{Q}$ constrains the spatial variation of that excitation. A phonon is a quantum of lattice vibration; a magnon is a quantum of a spin wave. Their different couplings make energy transfer alone insufficient to identify which was created.

Bertram Neville Brockhouse's aluminium experiment rotated a large single crystal, scanning analyzer angle for neutron groups. His vanadium comparison exposed the elastic resolution. Later magnetite measurements used a magnetic field intensity test to identify magnons.^[ref]

Successive orientations sample different wave vectors; analyzer settings distinguish outgoing energies. This supplies points on a dispersion relation, rather than only an angular diffraction pattern. Finite resolution can merge neighboring excitations; background, multiple scattering and processes involving several phonons can complicate interpretation. A lattice model is a testable explanation of selected features, not a guarantee that every spectral peak has the same origin.

At terminal speed, the downward excess weight is balanced by Stokes's law drag:The subtraction of the displaced water mass includes buoyancy. Hence the Stokes settling velocity isA density is needed but is not supplied. For the estimate, take a dense iron oxide represented by magnetite, with ${\rho }_p\simeq 5.2\times 10^3\mathrm{kg}{\mathrm{m}}^{-3}$, and water with ${\rho }_w\simeq 10^3\mathrm{kg}{\mathrm{m}}^{-3}$. This givesUsing the diameter for the particle Reynolds number gives $\mathrm{Re}\simeq {\rho }_w{v}_t(2a)/\eta \simeq 1.8\times 10^{-5}$, which supports the creeping-flow assumption. The model assumes a dilute isolated sphere far from walls and no imposed flow. The precise numerical speed depends on the unspecified oxide phase and particle density; the estimate is of order $10\mu \mathrm{m}{\mathrm{s}}^{-1}$.