![]() ![]() So while I've seen billiard balls with scratches and chips that might be larger than mountains on Earth might be at that scale, that is not what you think of when you think of how smooth a billiard ball is.Įverest is different than the Grand Canyon though, Mount McKinley in Alaska is actually taller base-to-peak as Everest has a higher base. That equates to about 220 km on the surface of the Earth, here's the pic compared to part of the grand canyon and everest:Īnd while the scaled-down grand canyon would be 8.2 micrometers deep, the variation in the marks is less than 1 micrometer (about 0.87). The pic from the site woliveirajr found is shows 1mm of an actual ball. The spec says 2.25+.005, not +/-, is that a typo or does it mean the balls must be at least 2.25 but not more than 2.255"? Most balls are actually manufactured to a higher tolerance, with good ones being under 0.001". The quoted tolerance ( specifications link) of 0.005 is for total size, not smoothness. I think vartec has the best answer so far. Just the non-spherical shape already disqualifies scaled down Earth as official billiard ball, allowable tolerance in diameter would be 28,326 m while difference between Earth's polar diameter and mean diameter is 28,513 m. 0.55μm scaled up to Earth size would be less than 125 meters.Īs for shape, which is really what the ☐.005 inches regulation is about, Earth is non-spherical, it's oblate spheroid with: Note, that variation is about 0.55μm, while 0.005 inches official tolerance for shape is 127μm. How does it compare with actual billiard ball, woliveirajr's answer is helpful: which means, that scaled down Earth's "smoothness" is equivalent to that of 320 grit sandpaper. With mountains reaching in excess of 8,000m, scaled down that would be 0.0015 in. In fact I find claim that sandpaper is smooth to be ridiculous. By that definition, medium sandpaper (grit particle size of 0.005 in) is also smooth, which doesn't quite go with my definition of smoothness. I disagree with definition of smoothness used by Discovery Magazine. If you shrank the Earth down to the size of a billiard ball, it would be smoother. Hey, those are within the tolerances! So for once, an urban legend is correct. The deepest point on Earth is the Marianas Trench, at about 11 km deep. The highest point on Earth is the top of Mt. Using the smoothness ratio from above, the Earth would be an acceptable pool ball if it had no bumps (mountains) or pits (trenches) more than 12,735 km x 0.00222 = about 28 km in size. ![]() The Earth has a diameter of about 12,735 kilometers (on average, see below for more on this). The ratio of the size of an allowable bump to the size of the ball is 0.005/2.25 = about 0.002. ![]() In other words, it must have no pits or bumps more than 0.005 inches in height. OK, first, how smooth is a billiard ball? According to the World Pool-Billiard Association, a pool ball is 2.25 inches in diameter, and has a tolerance of +/- 0.005 inches. The Discover Magazine blog addressed this in 2008 This strongly depends on definition of what smoothness is. ![]()
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