how would a 3D sphere be perceived if it was dropped through a 2D universe?

Answer 1

As an expanding, then contracting circle that appears first as a single point and disappears after contracting back to a single point.

Aloha

Answer 2

Mathematically speaking, a point increasing to a line the diameter of the sphere and decreasing back to the point before disappearing. It would look the same from all directions. However, in a real 2-D universe one could not see the point to start with, since the point could have no height. The height of a pencil line on a 2 graph is a third dimension.

Answer 3

It would be seen in the two dimensions intersecting the 2D universe.
Start as nothing before making contact, then a single point rapidly expanding into a large solid disc. After passing half way through the disc would rapidly shrink to a point and disappear.

Answer 4

Warren is right, but see Flatland for more detail.
The sphere example appears about 3/4 of the way through the document.

Answer 5

I would think a circle.

Answer 6

1D, silly!