Surface tension is the phenomenon that causes water to form into a sphere. Is that the same phenomenon that caused the stars and planets to be spherical (roughly spherical if you want to get technical)? Is it called something else when applied to interstellar bodies?
2006-06-27 08:13:05 · 6 answers · asked by habaceeba 3 in Science & Mathematics ➔ Physics
No, planets and stars are round because of gravity (to be more accurate, gravity is the curvature of space-time). This is a caused by a different phenomena than surface tension, which is due to the electromagnetic attraction between water molecules. The force of gravity and the electromagetic force are two different forces.
Surface tension does not actually make the drop round; air pressure does that. Surface tension simply gives the drop an outer wall like the wall of a balloon.
The reason that water drops form into spheres is the need to equalize the pressure inside the drop. Air pressure tries to squeeze the drop, and the internal pressure inside the drop pushes back - creating the internal pressure of the drop. This puts tension on the wall of the drop (Where the wall of the drop is caused by surface tension.). The geometric shape of the sphere minimizes the wall tension (http://hyperphysics.phy-astr.gsu.edu/Hbase/surten2.html). A shape with corners, such as a cube, would allow forces to be concentrated at the corner, which would smash the corner flat, or else cause the area around the corner to expand. A sphere allows for an even pressure distribution.
The pressure on a planet is caused by its own weight pulling its own matter inward. A sphere allows for an even distribution of gravational 'pressure'.
In other words, a sphere resists being crushed better than any other shape, so objects under internal or external pressure tend to become round (irregardless of what is causing the pressure).
2006-06-27 09:04:03 · answer #1 · answered by Randy G 7 · 1⤊ 1⤋
I'll mildly disagree with ronin's "few grams" statement.
There are many pictures of astronauts gulping large orbs of liquid floating in the spacecraft. These are larger than a few grams. I would venture to guess you could make an orb of kilogram scale. In a perfect world with no gravity and no fluid movement within the orb (fluid inertia would act to destabilize interfaces, breaking the orb into pieces), surface tension would act to allow infinitely large spheres. The lowest energy arrangement would be that of minimal surface area, or one big sphere.
Surface tension is a measure of the relative cohesive (molecule interacting with its phase) and adhesive (interacting with other phase) forces at an interface. Water forms a drop (instead of spreading to coat) on glass because water's cohesive force is much greater than its adhesive force to glass.
Since gases can't for interfaces with gases, there really would be no "surface" on which to act. And once things condensed enough to form liquid/plasma, the gravitational and internal inertial forces would be much more significant than the surface tension effects.
2006-06-27 15:43:03 · answer #2 · answered by scott_d_webb 3 · 0⤊ 0⤋
surface tension is only for very small amounts of matter. What is a small amount? Good question... all I can say is once you get past a few grams, it's overridden by other forces, such as gravity or electromagnetism.
2006-06-27 15:19:17 · answer #3 · answered by Anonymous · 0⤊ 0⤋
Well interstellar bodies get their shape due to their own gravitational pull, so to answer your question: No, it's not the same.
2006-06-27 15:17:35 · answer #4 · answered by chamrajnagar3 2 · 0⤊ 0⤋
no and i assume yes, but God put everything as it needs to be, i hope you don't believe in evolution
2006-06-27 15:17:00 · answer #5 · answered by Lauren H 2 · 0⤊ 0⤋
gravity for objects that large
2006-06-27 15:16:36 · answer #6 · answered by Anonymous · 0⤊ 0⤋