The motion of a fluid in a cylindrical container with a free surface following vertical impact

The effect of a sudden change in vertical velocity of a vessel partially filled with fluid is considered. It is shown that very small free surface disturbances can be amplified so strongly by a velocity change that instability can occur. This instability frequently causes a jet to emanate from the free surface. Conditions causing free surface disturbances in a vessel in free fall are considered and it is shown that a contact angle between the fluid and the wall of the vessel different from ½π radians can distort the surface in such a way that the amplification and instability upon vertical impact results in a central jet. The results of experiments of this effect are shown. The generation of waves due to transient side wall motions, such as those that might result from fluid pressure at impact, are considered in the appendix. It is shown that such waves would have a different form than those observed in the experiments.