One thing you can try is to imagine that the fourth dimension is brightness/color/temperature.
First imagine two 3d cubes lying in the same 3d space, but having opposite colors. A space of middle-grey is provided as a reference (this greyness takes up an entire 3d space). You imagine that if...
I think the best way to think about it is by thinking about how it is constructed.
You can think of a square as being constructed by translating a copy of a line segment in the perpendicular direction, and then connecting the corresponding vertices of the two copies of the line segment...
If the stick is very heavy, then another force acting on the stick is your hand. As you are keeping the stick still, this would mean the buoyant force ought to be independent of the weight of the stick. This leaves the shape/volume of the stick, and how far down in the water you stick it.
If...