Doppler Effect: waves emitted from a moving source. Source travelling faster than the waves propagate. Animation shows how a bow wave propagates from a ship. The ship pushes the water immediately in front and creates a wave (shown as a series of separate expanding rings for clarity). The wave fronts are shown propagating from their points of origin along the cruise path. As the ship sails forward, so the resulting waves create a swept back triangular expanding wave front (the bow wave).