In general, the wavefunction of a free particle is a superposition of infinitely many harmonic waves. In this Demonstration the probability distribution of momenta is assumed to be a Gaussian with average and standard deviation . The Demonstration allows you to follow the time evolution of the real and imaginary parts of the wavefunction, of the probability distribution function, and of (the real part of) the five partial harmonic waves corresponding to , . The circle in the wavefunction and probability distribution plots shows the positions of a classical particle moving with momentum p = < p >. The circle on the crest of each partial harmonic wave moves with the respective phase velocity. Units: , .