# What is the angle of a pile of hourglass sand? **URL:** \ **Category:** Factual Questions\ **Created:** [June 14, 2006, 2:47pm UTC](https://boards.straightdope.com/t/what-is-the-angle-of-a-pile-of-hourglass-sand/360684 "2006-06-14T14:47:04Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![jebert](https://avatars.discourse-cdn.com/v4/letter/j/ec9cab/32.png) [@jebert](https://boards.straightdope.com/u/jebert)\ **Post date:** [June 14, 2006, 2:47pm UTC](https://boards.straightdope.com/t/what-is-the-angle-of-a-pile-of-hourglass-sand/360684/1 "2006-06-14T14:47:04Z")
When sand drops from the upper chamber of an hourglass, it makes a pile in the lower chamber. The sides of the cone-shaped pile form at a specific angle. What is this angle? Is this angle the same regardless of what the material is? Or does it vary depending on the size, shape, or surface of the particles being dropped? Would smooth-surfaced spheres make the same angle as rough-surfaced cubes? ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [June 14, 2006, 3:13pm UTC](https://boards.straightdope.com/t/what-is-the-angle-of-a-pile-of-hourglass-sand/360684/2 "2006-06-14T15:13:43Z")
It’s called the [angle of repose](http://en.wikipedia.org/wiki/Angle_of_repose), and yes, it does vary with the shape and physical properties of the particles in a pile. > [@](#): > > The angle of repose has been experimentally shown to depend on the shape and roughness of the particles, typically measuring 22º for smooth spherical particles and 33 ± 2º for aeolian sand. Additionally, there is significant variation of qr (angle of repose) with the method of measurement. Smaller particulates can have a qr that is greatly affected by electrostatic interactions. [Martian dust](http://gsa.confex.com/gsa/2002AM/finalprogram/abstract_41188.htm) [BB’s, sand and silica powder](http://www.wtamu.edu/~crobinson/SoilWater/mounddr.html) ---
**Author:** ![robby](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robby/32/11048_2.png) [@robby](https://boards.straightdope.com/u/robby)\ **Post date:** [June 14, 2006, 3:32pm UTC](https://boards.straightdope.com/t/what-is-the-angle-of-a-pile-of-hourglass-sand/360684/3 "2006-06-14T15:32:54Z")
Materials have a characteristic “friction angle,” which is defined as the angle of internal shearing resistance expressed in degrees. It is dependent on how fine the material is, the angularity of the particles, and the amount of water present. More info: [http://www.brookes.ac.uk/geology/sedstruc/repose/landslid.htm](http://www.brookes.ac.uk/geology/sedstruc/repose/landslid.htm) [http://www.tubbs.com/geotech/geotech.htm](http://www.tubbs.com/geotech/geotech.htm) The term “angle of repose” is somewhat ambiguous, as noted in the first link. ---
**Author:** ![Fear\_Itself](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fear_itself/32/19637_2.png) [@Fear\_Itself](https://boards.straightdope.com/u/Fear_Itself)\ **Post date:** [June 14, 2006, 3:34pm UTC](https://boards.straightdope.com/t/what-is-the-angle-of-a-pile-of-hourglass-sand/360684/4 "2006-06-14T15:34:54Z")
> [@Squink](#): > > It’s called the [angle of repose](http://en.wikipedia.org/wiki/Angle_of_repose), and yes, it does vary with the shape and physical properties of the particles in a pile. I gotta ask: did you know that off the top of your head, or did you have to google? Hats off to you if that was just laying around the \*\*Squink \*\* noggin. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [June 14, 2006, 4:01pm UTC](https://boards.straightdope.com/t/what-is-the-angle-of-a-pile-of-hourglass-sand/360684/5 "2006-06-14T16:01:02Z")
> [@Fear Itself](#): > > I gotta ask:… I keep that one in a big pile of occasionally useful facts. 😉 ---
**Author:** ![gazpacho](https://avatars.discourse-cdn.com/v4/letter/g/6f9a4e/32.png) [@gazpacho](https://boards.straightdope.com/u/gazpacho)\ **Post date:** [June 14, 2006, 4:15pm UTC](https://boards.straightdope.com/t/what-is-the-angle-of-a-pile-of-hourglass-sand/360684/6 "2006-06-14T16:15:48Z")
> [@Squink](#): > > I keep that one in a big pile of occasionally useful facts. 😉 Facts are roughly shaped and can be piled high. ---
**Author:** ![Slithy\_Tove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/slithy_tove/32/18248_2.png) [@Slithy\_Tove](https://boards.straightdope.com/u/Slithy_Tove)\ **Post date:** [June 14, 2006, 4:33pm UTC](https://boards.straightdope.com/t/what-is-the-angle-of-a-pile-of-hourglass-sand/360684/7 "2006-06-14T16:33:41Z")
Driving through the northern states, you’ll notice that the sheds used by highway departments to store sand for road use in winter are pitched to match their contents’ angle. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [June 14, 2006, 5:21pm UTC](https://boards.straightdope.com/t/what-is-the-angle-of-a-pile-of-hourglass-sand/360684/8 "2006-06-14T17:21:26Z")
> [@gazpacho](#): > > Facts are roughly shaped and can be piled high. But not as high as horse manure.