We can use Equation (5.8) to obtain alternative mathematical expressions for the wave. Substituting for v=vλ in Equation (5.8) we obtain
y(x,t)=A sin(2πx/λ-2πvt) . (5.12)
We define the quantity 2π⁄λ as the wavenumber k, i.e.
k=2π⁄λ. (5.13)
Substituting for ω=2πv from Equation (5.11) and k from Equation (5.13) in Equation (5.12), we obtain
y(x,t)=A sin(kx-ωt). (5.14)
In addition, using the relationships vλ=v and2πv=ω, we have
v=ω/k . (5.15)