Why does a half-full water bottle oscillate when pushed?

[NZsam03]

Hi Guys,

In physics we are investigating the movement of a half-full water bottle accelerated by a constant force. The bottle moves in one direction, before slowing and then oscillating back and forth, similar to what was described in this thread.

https://www.physicsforums.com/showthread.php?t=519651

I have noticed that as you increase the amount of water, the oscillations increase, up to a point.

How is this whole phenomena explained?

Cheers

Sam

 

[Drakkith]

The frequency of the oscillations increases as you add water?