# If the Earth was a perfectly round ball of glass, and I dropped a ball on it, would it roll? **URL:** \ **Category:** Factual Questions\ **Created:** [September 8, 2016, 5:50pm UTC](https://boards.straightdope.com/t/if-the-earth-was-a-perfectly-round-ball-of-glass-and-i-dropped-a-ball-on-it-would-it-roll/765350 "2016-09-08T17:50:58Z")\ **Posts on this page:** 11\ **Page:** 3
**Author:** ![filmore](https://avatars.discourse-cdn.com/v4/letter/f/7993a0/32.png) [@filmore](https://boards.straightdope.com/u/filmore)\ **Post date:** [September 13, 2016, 3:13pm UTC](https://boards.straightdope.com/t/if-the-earth-was-a-perfectly-round-ball-of-glass-and-i-dropped-a-ball-on-it-would-it-roll/765350/41 "2016-09-13T15:13:54Z")
If the tea was in a funnel-shaped cup, would it slide up the side from the tidal force? ---
**Author:** ![The\_Great\_Unwashed](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/the_great_unwashed/32/4791_2.png) [@The\_Great\_Unwashed](https://boards.straightdope.com/u/The_Great_Unwashed)\ **Post date:** [September 13, 2016, 3:54pm UTC](https://boards.straightdope.com/t/if-the-earth-was-a-perfectly-round-ball-of-glass-and-i-dropped-a-ball-on-it-would-it-roll/765350/42 "2016-09-13T15:54:58Z")
> [@LSLGuy](#): > > … > On a non-rotating perfectly spherical perfectly uniform planet the gravitational potential is exactly perpendicular to the surface everywhere. No force would act along the surface of the planet to cause a stationary ball to move or a ball moving on a great circle to change course = 3D plane of motion. > > Any ball placed in motion not on a great circle will describe an interesting spiraling motion. > … How can one place the ball in motion \*not \*on a great circle? In your scenario (non-rotating perfect sphere), any (tangential to the surface) impulse applied to a ball would have it go off to describe a great circle. That’s just Spheres 101. ---
**Author:** ![dougie\_monty](https://avatars.discourse-cdn.com/v4/letter/d/439d5e/32.png) [@dougie\_monty](https://boards.straightdope.com/u/dougie_monty)\ **Post date:** [September 13, 2016, 7:12pm UTC](https://boards.straightdope.com/t/if-the-earth-was-a-perfectly-round-ball-of-glass-and-i-dropped-a-ball-on-it-would-it-roll/765350/43 "2016-09-13T19:12:07Z")
This issue was taken up once in _Games_ Magazine. To sum it up, the Earth’s surface texture was determined to resemble the surface of an orange. ---
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [September 13, 2016, 7:26pm UTC](https://boards.straightdope.com/t/if-the-earth-was-a-perfectly-round-ball-of-glass-and-i-dropped-a-ball-on-it-would-it-roll/765350/44 "2016-09-13T19:26:30Z")
> [@dougie\_monty](#): > > This issue was taken up once in _Games_ Magazine. To sum it up, the Earth’s surface texture was determined to resemble the surface of an orange. Does that mean the white covering Antarctica is, in fact, just navel lint? Ewwww… ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 13, 2016, 7:38pm UTC](https://boards.straightdope.com/t/if-the-earth-was-a-perfectly-round-ball-of-glass-and-i-dropped-a-ball-on-it-would-it-roll/765350/45 "2016-09-13T19:38:03Z")
The Earth is far smoother for its size than an orange. ---
**Author:** ![dougie\_monty](https://avatars.discourse-cdn.com/v4/letter/d/439d5e/32.png) [@dougie\_monty](https://boards.straightdope.com/u/dougie_monty)\ **Post date:** [September 13, 2016, 10:44pm UTC](https://boards.straightdope.com/t/if-the-earth-was-a-perfectly-round-ball-of-glass-and-i-dropped-a-ball-on-it-would-it-roll/765350/46 "2016-09-13T22:44:34Z")
FWIW, here’s the letter printed in the January 1986 issue of _Games_ on this topic: "Martin Gardner states in ‘It’s a Small World’ (Wild Cards, October [1985–d.m.], page 55) that if the earth were reduced to the size of a billiard ball, the mountain peaks and ocean basins would be so small that the planet would feel ‘as smooth as ivory.’ "Not so. Using a device that records surface texture, I measured the surface of a standard 2 1/4-inch billiard ball and found a surface roughness of 120 microinches (a microinch is one-millionth of an inch). This is very smooth, considering that, if this billiard ball were the size of the earth, 7,927 miles in diameter, the highest ridge would be only 2,232 feet. “However, Mount Everest is 13 times this height; at 29,028 feet, it would register as a bump of 1,560 microinches. The Mariana Trench, at 36,198 feet, would be a valley 1,950 microinches deep. At that magnitude, one can definitely see and feel the surface features.” –D. C. Hidinger New Philadelphia, OH _[The surface Mr. Hidinger describes is similar to the skin of an orange.–Ed.]_ ---
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [September 13, 2016, 11:50pm UTC](https://boards.straightdope.com/t/if-the-earth-was-a-perfectly-round-ball-of-glass-and-i-dropped-a-ball-on-it-would-it-roll/765350/47 "2016-09-13T23:50:10Z")
Wrinkles on an orange are far deeper than 0.0035" I should think … ---
**Author:** ![Boyo\_Jim](https://avatars.discourse-cdn.com/v4/letter/b/87869e/32.png) [@Boyo\_Jim](https://boards.straightdope.com/u/Boyo_Jim)\ **Post date:** [September 14, 2016, 1:31pm UTC](https://boards.straightdope.com/t/if-the-earth-was-a-perfectly-round-ball-of-glass-and-i-dropped-a-ball-on-it-would-it-roll/765350/48 "2016-09-14T13:31:32Z")
According to the specifics of the OP, the earth is perfectly round and smooth, but that is not a guarantee that its center of gravity is exactly in the center of the sphere, or that it’s rotation is without any perturbations, or that its orbit is spherical. Given the conditions specified, it seem definitely possible that the small sphere placed on the eath’s spherical surface may roll. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [September 14, 2016, 3:07pm UTC](https://boards.straightdope.com/t/if-the-earth-was-a-perfectly-round-ball-of-glass-and-i-dropped-a-ball-on-it-would-it-roll/765350/49 "2016-09-14T15:07:07Z")
As always, it is nice to note the lack of [Asperity (materials science) - Wikipedia](https://en.m.wikipedia.org/wiki/Asperity_(materials_science)) in a GQ OP and subsequent discussion. Although with the introduction of the citrus motif one senses a degree of [Asperity (geotechnical engineering) - Wikipedia](https://en.m.wikipedia.org/wiki/Asperity_(geotechnical_engineering)). ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [September 14, 2016, 4:49pm UTC](https://boards.straightdope.com/t/if-the-earth-was-a-perfectly-round-ball-of-glass-and-i-dropped-a-ball-on-it-would-it-roll/765350/50 "2016-09-14T16:49:43Z")
Both your links are broken. The correct ones are [Asperity (materials science) - Wikipedia](https://en.m.wikipedia.org/wiki/Asperity_(materials_science)) and [Asperity (geotechnical engineering) - Wikipedia](https://en.m.wikipedia.org/wiki/Asperity_(geotechnical_engineering)) SDMB’s parser that auto-converts text like \*http… \*to clickable URLs will screw up every time if the URL ends in a “)”. As many wiki urls do. The parser will leave the final “)” out of the actual url but include it in the visible text. Note in **Leo** ’s post the final “)” isn’t blue and isn’t underlined. That’s the problem. Contrast those with my links here. The fix is to either [Go advanced] then move the final “)” inside the tag, or insert the urls using the internet link button above the text entry window. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [September 15, 2016, 12:26am UTC](https://boards.straightdope.com/t/if-the-earth-was-a-perfectly-round-ball-of-glass-and-i-dropped-a-ball-on-it-would-it-roll/765350/51 "2016-09-15T00:26:14Z")
Thanks for the corrections. Nothing ruins a funny like a speech impediment. Seriously, though, finding out that “asperity” is a thing–_the_ thing, in fact for this OP–is one of the typical pleasures of GQ. [Previous page](https://boards.straightdope.com/t/if-the-earth-was-a-perfectly-round-ball-of-glass-and-i-dropped-a-ball-on-it-would-it-roll/765350.md?page=2)