Fluids in Weightlessness (1975)

[Music] [Applause] [Music] it's hard to believe this is the normal behavior of water drops in weightlessness it's even more remarkable that these free floating drops can help us understand Atomic nuclei crystal growing even the formation of [Music] [Applause] [Music] stars scientists in many fields are vitally concerned with fluid Behavior I was the scientist pilot on the second man mission of the Skylab space station our research included many experiments with fluids demonstrations which can't be done on the ground I'd like to share with you some of the discoveries we made and some of their implications [Music] in the weightless environment of an orbiting spacecraft surface forces dominate the behavior of water drops this surface tension is caused by the inward pull of interior molecules on the ones near the liquid surface such cohesion prevents The Escape of molecules from the liquid the same surface tension acts on Earth too but here Gravity and the need for support forces prevent drops from coming into equilibrium under the influence of surface forces alone small drops of water do form but they last too short a time for us to manipulate them on a hot surface tiny almost spherical drops are preserved by their own cushion of vapor under some conditions surface tension effects are easily visible on the ground as in making soap bubbles in Flight we found it difficult to keep keep a water drop where we wanted it for close examination or for the [Music] camera we were able to take advantage of surface forces by tethering blobs with a thread incidentally all these drops are just water with ink or juice added for [Music] visibility the adhesive or sticking aspect of surface tension was demonstrated nicely in Skylab here you see water pulled up by a drinking straw in this unique demonstration the crewman pinched the drop too rapidly for it to change shape smoothly the resulting instability led to partial breakup of the [Music] drop handling of fluids was of course required every day to quench our thirst the usual way was to use an accordion-like plastic bottle to squeeze the drink into our mouths however Bill POG wanted to see if adhesion would permit the use of an open type drinking vessel a difficult operation to do in zero gravity every time you try to take a drink in zero Gra of course the water just goes every direction and and this surf the uh the water is contained in this container so strongly that I can actually squirt the water in with this water gun and it will stay in there that's going in there with some degree of force so in the process of actually doing this experiment we we discovered a fairly interesting fact now I'm going to take a drink of the first really first cup I knowah that was actually been used in zero gravity works fine freely suspended or lightly tethered a water drop is spherical in equilibrium the attractive surface forces produce this most symmetrical of shapes when a water drop is rotated it is elongated by centrifugal forces that tend to pull a drop apart meanwhile the cohesive surface forces act to hold the drop [Music] [Applause] [Music] together a drop rotating fast enough will break apart scientists are puzzled by the long delay before this one split the question is Complicated by the presence of an air bubble which may have weakened the neck of the drop in any case the higher the speed of rotation the more the water drop takes on a so-called dog bone shape this shape is also characteristic of some te ties which are glassy rocks whose very presence on Earth is mysterious the te ties evidently were once hot molten and tumbling in midair some of them cooled rapidly and froze into shapes like the elongated Skylab water drops others froze into even stranger shapes in composition te ties resemble neither volcanic material nor meteorites they may have formed in the liquefying impact of a fiery meteorite with sand on earth they could have come from the moon or another planet they might be material kicked onto a collision course with Earth by a huge [Music] meteor Nature has also given the splitting drop a place in a submicroscopic world of atoms in some ways an atomic nucleus behaves just like a liquid drop a heavy nucleus like uranium contains numerous protons and neutrons nucleons which attract each other like the countless molecules of a water drop therefore a nuclear drop also has surface tension holding it together but the protons are positively charged they repel each other with forces almost as strong as attractive nuclear forces the balance is so delicate that even small disturbances can trigger nuclear fishing from the tiny world of the atom to the stars and planets is an enormous jump but our analog of fluid Behavior also applies to the gas and dust drifting through the universe the Sun and planets may have condensed from a rotating shrinking fluidlike Cloud a billion miles across as such a cloud contracts under the influence of gravity it forms a disc and it heats up and then rotates faster and faster what happens next is poorly understood but many scientists feel that fragmentation of the cloud is most likely if the cloud breaks into one large piece and many small ones the result could be a solar system like [Music] ours if there are several large fragments each May condense into a star presumably binary Stars were formed in just this way astronomers have observed countless examples with periods of Revolution ranging from a few hours to hundreds of years galaxies may also have Arisen from fluidlike clouds of gigantic Mass a rotating spiral of 100 billion stars is a typical stable state for such an enormous system but stranger shaped galaxies are also common the Dynamics of Galaxy formation is one of the great unsolved puzzles of astrophysics although most of the applications of our demonstrations lie in the theoretical realm some may soon be turned to practical use our most thorough investigation of fluid behavior on Skylab has indeed aroused new interest in several fields of Technology here for example Ed set up a rig for rotating two socket wrenches with a zone of colored water between them and these mounts are pretty much the same as hold up the TV Camera line them up taking some of our tools which are extension shafts for uh some of the bits that we have and mounted them in here so that they're free to turn we'll be placing a fluid in between the two here which you'll be able to get a closeup view on this [Applause] camera and then we're going to turn it we're going to turn both of them simultaneously using this string and Rod pulling it up we can change the speed we can rotate them in opposite directions and we can also move the distance apart we placing a similar Arrangement is important in growing large High purity rods of semiconductor material vital in the electronics Industry on earth a molten rotating zone of silicon or geranium is uniformly cooled between vertical rods convection currents due to gravity are still present limiting the size and purity of the crystals in orbit there is negligible convection bigger crystals can be grown in the 1980s this technique may be used to grow semiconductor crystals of unprecedented [Music] quality it is extremely difficult to predict exactly what will happen when two drops [Music] collide [Music] but the collision and merging of drops is important in [Music] nature in the fusion of atomic nuclei two nuclear drops join to form a heavier nucleus by studying events like these physicists May learn how to make super heavy elements [Music] the Collision of tiny drops is also crucial to development of a rainstorm in certain clouds raindrops form by a complex process of condensation and merging of microscopic droplets this process is not completely understood detailed studies of water drops in weightlessness could lead to a breakthrough in Cloud [Music] physics in the near near future many more experiments with liquids will be done in orbit applications are possible in meteorology Materials Handling nuclear physics and astronomy but already we have learned that a liquid drop in weightlessness can model the behavior of a tiny Atomic nucleus or a giant Galaxy with models of such convenient size we are thus given a new view a glimpse into world of the very small and the very large