Question

Why can I assume that the volume of water in a glass would have a similar relationship to the height of water in the glass?

Answer 1

liquids don't compress the way gasses can. Assuming you've got 2 glasses of equal size, the ratio of their heights will be proportional to the ratio of their volumes

Answer 2

I think the better answer is.. it is only true when you consider the class has a constant area..

in this case.. the volume = \[\pi r^2 h\]

since the area is a constant
\[v \ \alpha \ h \]

this is not true if you had something like this



in this case the area keeps changing and so volume not proportional to height