# Cubinder (EntityTopic, 14)

(Difference between revisions)
 Revision as of 15:50, 26 March 2017 (view source) (→Equations)← Older edit Revision as of 17:58, 24 April 2018 (view source)Newer edit → Line 49: Line 49: == Net == == Net == - The net of a cubinder is a [[cube]] surrounded by four cylinders: + The net of a cubinder is a square prism surrounded by four cylinders: -
<[#embed [hash E1DEP0C53JK6MRZHKYP1RVJ3AW]]>
+
<[#embed [hash RPQ54H9ZJ1S4WA06VMPAT4YKTJ]]>
+ + == Cross-sections == + + Round cell-first: + <[#embed [hash 5FBS0ZWNFQTA48RTACSWM2NKM7]]> + Cylinder-first: + <[#embed [hash TBMWG97G7BMPT1E9MA6XPCP4PQ]]> + Disk-first: + <[#embed [hash 2AJRT8JXT9G3PAKXV4RSPS3DM1]]> + Round face-first: + <[#embed [hash RDS3RK7R3SJPR5K7QV2FEVW6G3]]> + Edge-first: + <[#embed [hash HBJR82FNG270JGX9VFKVGGH98A]]> == Projection == == Projection ==

## Revision as of 17:58, 24 April 2018

A cubinder is a special case of a prism where the base is a cylinder. It is also the limiting shape of an n,4-duoprism as n approaches infinity. In other words, it is the Cartesian product of a circle and a square.

## Equations

• Variables:
r ⇒ radius of the cubinder
h ⇒ height of the cubinder along z and w axes
• All points (x, y, z, w) that lie on the surcell of a cubinder will satisfy the following equations:
x2 + y2 = r2
abs(z) ≤ h
abs(w) ≤ h
-- or --
x2 + y2 < r2
abs(z) = h
abs(w) = h
total edge length = 8πr
total surface area = 4πr(r + 2h)
surcell volume = 2πr(rh + h2)
bulk = πr2h2
[!x,!y] ⇒ square cuboid
[!z,!w] ⇒ cylinder

## Net

The net of a cubinder is a square prism surrounded by four cylinders: ## Projection

The cubical cylinder, or cubinder for short, is one of the ways to generalize the 3D cylinder to 4D. This object can be constructed by extruding a 3D cylinder along the W-axis by a unit distance. The following is a diagram of the cubinder in parallel projection: The following is a perspective projection of the cubinder: The inner cylinder is actually the same size as the outer cylinder, but appears smaller in perspective because it is farther away. Also, the upper and lower frustums connecting the inner cylinder to the outer cylinder are actually themselves regular cylinders; but they appear as frustums because they are being viewed at from an angle.

And the next diagram shows another perspective projection, this time with the cubinder rotated 45 degrees in the ZW plane. Here, it is more apparent that the cubinder consists of four 3D cylinders joined at their circular ends. What is not so apparent, however, is that their round surfaces are joined by a square torus. This is the torus generated by rotating a square in the ZW plane (displaced in the Y direction by one unit) in the XY plane. One could also construct it by extruding the round part of the cylinder along the W-axis.

These diagrams do not have hidden surfaces removed, so that the whole structure of the cubinder is more apparent. However, a 4D being looking at the cubinder would not see the entire structure simultaneously. The inner cylinder in the second diagram would not be visible, for example, and neither would the two inner cylinders in the second diagram.

The reason for the cubinder's name is that one of its possible projections is the 3D cube: The blue edges in the cube show where the 4 circular ends of the cylinders are. They have collapsed into a single line in the diagram because they are perpendicular to the direction of projection.

## Rolling

There are 4 circular surfaces on the cubinder, on which it may roll. All 4 surfaces, however, can only rotate parallel to the same plane, and hence the cubinder can only cover the space of a line by rolling. (This may sound counterintuitive to our 3D-centered understanding of rotation, because the 4 cylinders are in 2 perpendicular pairs, and so have perpendicular central axes. In 3D, two perpendicular central axis define two different planes of rotation. However, in 4D, rotations don't happen around an axis, but around a plane. The perpendicular central axes of the cubinder are actually both perpendicular to the plane of rotation. As one can see from the diagrams above, all circular sections of the cubinder lie parallel to the same plane, and hence can only rotate in that plane.)

 Notable Tetrashapes Regular: pyrochoron • aerochoron • geochoron • xylochoron • hydrochoron • cosmochoron Powertopes: triangular octagoltriate • square octagoltriate • hexagonal octagoltriate • octagonal octagoltriate Circular: glome • cubinder • duocylinder • spherinder • sphone • cylindrone • dicone • coninder Torii: tiger • torisphere • spheritorus • torinder • ditorus

 14. 22Duocylinder 15. 211Cubinder 16. 1111Tesseract List of tapertopes

 12. (IIII)Glome 13. [(II)II]Cubinder 14. <(II)II>Dibicone List of bracketopes