Rocks and pebbles polished in creeks and the ocean are never perfect spheres. Why not?

Question

I assume the force of gravity prevents rocks and pebbles from becoming perfectly round. If they were polished in outer space would they be spherical?

Lots of good answers. True, there is no such thing as a perfect vacuum. If it is possible in space, how could it be done?

I don't think any of the answers are sensible. The vacuum is irrelevant to the problem, and logically contradictory. Does anyone know a real answer to this question??

Answer 1

Because in order to be "perfectly round" you need a distance in order to roll. By the time they roll any distance at all they are already in the ocean where the current no longer drags them across a scarring or damaging creek-bed that rubs their surface away. Gravity or lack there of also is no indicator of an ability to create spherical objects. However, if you so desired and had the technology, free fall would aid in this, if you knew what you were doing.

Answer 2

If you think about it, people who polish gemstones work hard to get the "perfect polish"; they have to look at each spot on the gem and determine just what amount of force, grit/polish and other such factors need to be applied.

In nature, the forces that polish the stones (moving water, bits of sand/sediment, etc) are less than regular, and there's nobody to analyze the stone to determine just what needs to be done.

I imagine that, given the uneven nature of the "rough" stone and the unpredictable nature of, well, Nature, there is a chance (albeit incredibly slim) that a rough stone could be polished to a perfect sphere.

Now let's assume that in order to create a perfect sphere, the stone would have to be in a state of suspension, revolving and pelted by sediment/sand/etc. In response to the issue of gravity, based on what I've laid out above, I think gravity might have a small amount to do with the natural polishing; simply, the stone will have to have larger forces acting on it to keep it in a continuous state of buoyancy, or else the rubbing against the bottom of the river/lake/ocean will cause a rougher polish that could ruin the "perfect" polish the small bits of sediment could accomplish.

But "never" being a perfect sphere, I believe it's possible. Perhaps a pebble you see today was actually a perfect sphere several years ago, but over time has eroded past that point.

Just my thoughts :-)

Answer 3

Perfect cube or any other shape, gravity or weightlessness, nothing has a perfect center-of-gravity balance point whereas the friction created by an abrasive substance (water, air, etc) will allow an object to result in a "perfect sphere." Even a perfectly sperical object subjected to a continuous abrasive substance will "flatten out" as a result of gravity as it sits on the bottom of a creek, ocean, etc.

Answer 4

As you mention, gravity plays a major role, both in smoothing process, as well as in the structure of the initial pebbles. Thus the structure of the levels inside each pebble is composed by liner, rather than spherical levels! SO, when they hit each another, the optimum result could not be a sphere!

Answer 5

If one were to put a perfect cube rock into a creek, it may come out as a perfect sphere. However, usually rocks that fall into creeks have a relatively wide side which they will tend to settle towards, which will prevent them from becoming spherical.

Answer 6

As long as there is matter surrounding the sphere the matter interacts with the sphere and deforms it. "Perfect" is an impossibility unless inside of a perfect vacuum, which is also impossible.

Answer 7

Simple. Perfect geometry DOES NOT and cannot EXIST in nature. Please no snowflakes or ice crystals as examples ,those are RANDOM imperfect geometry. Imperfect spheres are random or accidental numbers in physical space. Perfect numbers in physical space is perfect geometry in physical space. A perfect circle is accidental of perfect geometry, imperfect circles are accidental of imperfect geometry. EX: random numbers in space = random shape, perfect numbers in space = perfect shape, unless manipulated by intelligence perfect geometry will not appear in nature.

Answer 8

yup. ball bearings made in space are perfectly spherical so why not polished rocks though i don't know how you'll polish them

Answer 9

I agree with him ^