In this study, we employed a high-speed camera to investigate the sloshing phenomena due to a sudden stop of a container which moved at a constant speed. Two different containers were used. One has a square cross section; the other one has a rectangular cross section. The sloshing wave motions on the free surface were described for these two containers and their features were discussed. Through the particle image processing, we clearly revealed the velocity field of sloshing flow. In addition, we also measured the fundamental resonance frequency for sloshing in the square container and found it agreed quite well with the theoretical value.