# Formula: Group Velocity (Oscillation of a Monatomic Chain) Spring constant    Mass    Lattice constant    Wave number

## Group velocity

Unit
Velocity with which a lattice vibration propagates in the crystal. It follows from the derivative of the dispersion relation $$\omega(k)$$ of the lattice vibration with respect to the wavenumber $$k$$.

## Spring constant

Unit
Spring constant for the coupling between neighboring lattice planes (atomic chains) of the crystal lattice.

## Mass

Unit
Mass of an atom inside a lattice chain.

## Lattice constant

Unit
Lattice constant is the distance between adjacent lattice planes at equilibrium.

## Wave number

Unit
Wavenumber represents the number of oscillations performed within the wavelength $$\lambda$$: $$k = \frac{2\pi}{\lambda}$$. The sign of the wavenumber indicates the direction of propagation of the oscillation.

## The Most Useful Physics Formula Collection on the Internet

+ Perfect for high school and undergraduate physics students
+ Contains over 500 illustrated formulas on just 140 pages
+ Contains tables with examples and measured constants
+ Easy for everyone because without vectors and integrals