A travelling wave in Python

You will write the equation of a travelling wave as functions, and then show that the pattern moves along at the speed $\omega/k$.

The idea. A wave moving towards $+x$ is $y = a\sin(kx - \omega t)$, with $k = 2\pi/\lambda$ and $\omega = 2\pi f$. A snapshot taken a time $\Delta t$ later is the same shape, moved on by $v\Delta t$.

Your tasks.

1. In wave_number, return $k$ for the wavelength lam.
2. In displacement, return $y$ at the place x and the time t.
3. In wave_speed, return the speed of the wave from k and w.