Why do you think fish bowl above is considered a system but an empty fish bowl is not

A fish bowl can be described as an open system. It contains several types of matter that are interacting with one another. In this type of open system, matter can enter from the surroundings and matter can escape to the surroundings. However, an empty fish bowl has no matter present to enter or escape to the surroundings. Therefore, an empty fish bowl is not a system.

The kinetic energy of the liquid increases. hope this !

For a collision to be successful you need 2 different objects