I want to describe the movement or position of an inner material inside an outer sheath, as the inner moves through the outer. Can anyone think of some kind of verb, spatial preposition or any other word or phrase?

For example, I'd like to describe the relative position of a cob of corn inside a bun, or the movement of a worm inside its tunnel.

In particular, I have something like an infinitely-long core of lego-bricks inside an infinitely long tube of different-sized lego-bricks, and I want to talk about the movement of the core along the tube. I can't talk about the absolute position, as there's no end-points to compare to, so I have to refer only to the relative positions of the bricks themselves.

Thanks for any help.

  • Why should you need a special word for this? I don't know if it's actually possible, but in principle you could walk round the donut-shaped torus of the Large Hadron Collider at Cern. And in principle, being circular, that has no "end". What is so special about your context? Mar 4, 2014 at 12:25
  • Like FumbleFingers said: If you don't have some reference point, e.g. a red brick in the tube wall, you can't have a relative position. You can define motion but not position. Mar 4, 2014 at 12:30
  • 2
    Paul Simon would say, the nearer your destination, the more you slip sliding away.
    – bib
    Mar 4, 2014 at 12:59
  • Maybe I didn't explain this very clearly, sorry. Let's say, for the sake of example, that the outer bricks are 3cm long and the inner ones are 2cm long. If I mark a spot on the tube, I can tell if I've shifted the core along by, say, 0.5cm, even without having any end points. (I can't tell just by looking whether it's been shifted by 2cm, because it looks like nothing's changed, but that's besides the point.) I'm looking for a good name for this 'shift'.
    – Samizdis
    Mar 4, 2014 at 13:56
  • 1
    @Gyppo: oic. Perhaps [lateral] [relative] motion. In such a context it's largely meaningless to think of specifically either the core or the containing tube moving, since the effect would be the same if that part remained static and the other part moved. But since you speak of "pulling the core through", maybe you should assume the tube is "static" in absolute space, and that the core moves by being "drawn along". Mar 4, 2014 at 14:07

7 Answers 7


I would say displacement for the distance traveled. (Independently from Carl Witthoft.) I can't think of a word for the act of moving, but since this is happening in a 1-dimensional manifold, motion suffices: the motion of the object through the tube, or the relative motion of the object and the tube. From time t to time t', there is a displacement of 3mm in one direction.

If the object can also “wiggle” inside the tube, this wiggling would be radial motion. Motion alongside the tube is axial motion.

Warning: I am neither a native speaker nor a physicist.

  • Thanks, it's a good word but unfortunately in this context displacement might mean that the crystal is displaced by something else, water for example. 'Axial' is quite useful too, thanks.
    – Samizdis
    Mar 4, 2014 at 14:41

You could consider the verb snake, which means to move, twist or wind, to make a course through (in the manner of a snake).

It's not immediately obvious from the definition that this is a fit, but some examples come to mind that are similar to your example:

He snaked his way through the surrounding crowd.

You clean your saxophone by first snaking this string through it and pulling the attached cloth all the way through.

Snake this auger through the pipe to clean it.

The optic fiber was installed without disrupting traffic. We simply snaked it through an existing utility conduit that ran between the two sites.


I believe the verb you are searching for is to squirm. I may be wrong.


Although your parts are bricks and do not have an axis of symmetry, I think you could use "concentric" motion, which covers either sliding or rotating along or about a common axis. Another similar word is "coaxial".

"Concentric" means "of or denoting circles, arcs, or other shapes that share the same center, the larger often completely surrounding the smaller", so concentric motion is motion of objects along or about a common axis. For example, a rod sliding or rotating inside the center of a tube. If you look at it from the end, the centers of the tube and the rod remain fixed as the rod slides in and out or rotates.

"Coaxial" means "having a common axis", so coaxial motion would be motion along or about a common axis. It's similar to "concentric" but explicitly applies to three dimensions.

  • Can you add the definition of "concentric" to your answer? It will help make this answer more useful. :)
    – MrHen
    Mar 18, 2014 at 15:12

I think we can call it "inner sliding motion" if we assume that there is a friction.

Sliding is a type of frictional motion between two surfaces in contact. This can be contrasted to rolling motion. Both types of motion may occur in bearings.

For example, in this animated gif, chocolate cookies are sliding inside metal bars:

enter image description here Source: http://gizmodo.com/5954979/i-cant-stop-watching-this-ice-cream-sandwich-factory


Initial thoughts on this request bring to mind "lateral translation". The idea you present reminds me of the action of suction or pneumatic pressure such as those used to transfer tubes of messages within office buildings. Glide may be another option.


the word Progress (and its derivatives, like progression)could be used to describe a movement with purpose, direction need not be specified, "as the corn progresses through the bun", but it does however imply self propulsion and potentially motivation. A worm would progress through the earth in order to reach....

in your case, you could use "as the inner bricks progress through the shell of outer bricks..."

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