What is an example of a cross section?

Answer 1

take a 3-dimensional object, and picture a sharp knife cutting it.

More correctly, a "plane" (thus, 2-dimensional) going through it.

The point at which the knife - or plane - intersects or touches the 3D object, is its cross section.

In a simple case, for example a sphere (meaning a "ball" with no middle, only a surface) then ANY cross section of it will be a "circle", (if you are "just touching it" you'd have a point, which is -- sort of like a circle of 0 radius).

That is the geometric definition.

A "practical" definition might be the "cross section of an airplane body". In THIS case your cross section would show the outer skin, the frame, the inner wall, the seats, floor, air ducts, wiring, hydraulic lines (which would look like 'o' because you presumably sliced it perpendicular to the way it is going), etc. Thus a computer aided design or drafting (CAD) program could show you a "slice" of something - a cross section - at any point, to for example see how close something is to something else, etc.

Another cross-section example would be CAT scans - such as for a brain problem - each computer generated slice is a "cross section" of the brain at that distance say from the top of your head (though it could be shown front to back, or probably any angle) - but what you are seeing is the intersection of a "plane" and the object.