Visualising one dimension in real/physical world.

Question

How can we visualize one-dimension in real/Physical world? Does any body have an example? Often people refer to one-dimension as motion being in a straight line. However motion in a straight line can be two dimensional. For Instance, The graph of $f(x)=x$, for every $x\epsilon \mathbb{R}$. Thanks in advance.

Answer 1

Even in the graph of $f(x) = x$, there is one line. It is diagonal, and it seems like it's going in the up-right direction, but it only has one direction in the sense that it cannot escape the line.

Answer 2

Consider an ant stuck on a very thin wire.

Any straight line graphed on a plane.

Power lines in a picture.