cwes99_03 Posted November 4, 2005 Report Share Posted November 4, 2005 The shape of the drop is directly related to at least three things that I can think of. 1) Relative velocity of the falling drop in respect to the surrounding molecules of air. 2) Volume of the rain drop (which of course depends upon the pressure exerted on the drop by the surrounding molecules. 3) the chemical makeup of the drop (salinity, soluble gasses, etc.) Now instead of talking about the shape, we are talking about the transformation of drops as they fall. There are in fact many shapes that the drop transitions through as it falls dependent upon the variables mentioned above and possibly others i'm not considering. Quote Link to comment Share on other sites More sharing options...
CraigD Posted November 4, 2005 Report Share Posted November 4, 2005 … Now instead of talking about the shape, we are talking about the transformation of drops as they fall. There are in fact many shapes that the drop transitions through as it falls dependent upon the variables mentioned above and possibly others i'm not considering.Indeed. The basic picture I get from following links such as the above is one of large drops flattening until they form a “parachute shape” with most of their mass around its rim, which then breaks up into smaller, slower-falling drops, which collide with and are absorbed by other large and small drops, producing large drops that flatten into the parachute shape, etc. A wonderful sequence! It’s frustrating that, for all our video recording capabilities, water droplets remain very difficult to see, so, while we can visualize this process, we can’t easily see it actually occurring. If I’m judging a science fair project and come across a project than manages to video raindrops, I’m giving it a prize, even if its methodology’s a mess! Quote Link to comment Share on other sites More sharing options...
Jay-qu Posted November 4, 2005 Report Share Posted November 4, 2005 I understand that rain drops can take a few different shapes - but not perfectly sphereical ones. So my question is why do we get round hail? Quote Link to comment Share on other sites More sharing options...
Turtle Posted November 4, 2005 Report Share Posted November 4, 2005 I understand that rain drops can take a few different shapes - but not perfectly sphereical ones. So my question is why do we get round hail? Hail isn't always round (spherical), & the smaller it is, the less chance it has to get spherical. Hail is created when precipitation freezes, falls, & then is pulled against gravity by updrafts, As it rises it collects more water which then frezzes to form another layer of ice. Once the overall weight of a stone is sufficient to negate the updraft, the hailstone falls to the ground. Because the hailstone is solid as it forms, it may tumble in the air which distributes the new layers more or less evenly. A perfectly spherical hailstone I expect is rather anomolous. :hihi: Quote Link to comment Share on other sites More sharing options...
steelengineer Posted November 4, 2005 Report Share Posted November 4, 2005 Convection is nothing to do with gravity. As long as there is air to be transfered heat, convection takes place. Gravity pulls the air. If there is no gravity, there is no air and the convection also never happens. the density of air is lower in zero g, which interns to oversize the water doplet volume and the overall relative humidity ratio within the droplet boundary maintains. :hihi: the way i understand convection is that, the lower density fluid (liquid or gas) escapes to the top making the higher density fluid fill in the empty space. this is because the higher desity fuid has more mass per volume, and hence is pulled strongly downwards due to gravity relative to the lower density fluid. so where did i go wrong? the inclusion of vaccum in the question no doubt removes all possibility of convection happening since there is no mass! and If there is no gravity, there is no air what does the existance of air have to do with gravity, and vice versa????? :lol: Quote Link to comment Share on other sites More sharing options...
Jay-qu Posted November 4, 2005 Report Share Posted November 4, 2005 I understand how hail is created but around my house we always get round hail... ok ill admit its not perfect its slightly bumpy like a golf ball but the general shape is round oh and steelengineer without gravity our planet would not hold the atmosphere in place - it would float away into space, I think thats what insight was getting at :hihi: Quote Link to comment Share on other sites More sharing options...
Turtle Posted November 4, 2005 Report Share Posted November 4, 2005 I understand how hail is created but around my house we always get round hail... ok ill admit its not perfect its slightly bumpy like a golf ball but the general shape is round___Interesting observation JayQ. Given that a dimpled sphere (golf ball or otherwise) travels farther than a smooth sphere given the same applied force, may we assume these hailstones travel farther in the updraft & so stay longer & so grow thicker layers? ___Theorizing a 'perfectly' spherical hailstone is one thing, but finding one is another. On further thought, I'll stick my neck out & say they don't exist. Fractal boundary & all that. :hihi: :cup: Quote Link to comment Share on other sites More sharing options...
Jay-qu Posted November 4, 2005 Report Share Posted November 4, 2005 ___Interesting observation JayQ. Given that a dimpled sphere (golf ball or otherwise) travels farther than a smooth sphere given the same applied force, may we assume these hailstones travel farther in the updraft & so stay longer & so grow thicker layers? ___Theorizing a 'perfectly' spherical hailstone is one thing, but finding one is another. On further thought, I'll stick my neck out & say they don't exist. Fractal boundary & all that. :hihi: :cup: Interesting idea... and yeah well nothing is perfect, but if there was one finding would be one thing - storing would be another, you cant touch it because it would melt unevenly... next time it hails i will take a few samples and if i get around to it i might photograph them and post it. Quote Link to comment Share on other sites More sharing options...
Turtle Posted November 4, 2005 Report Share Posted November 4, 2005 Interesting idea... and yeah well nothing is perfect, but if there was one finding would be one thing - storing would be another, you cant touch it because it would melt unevenly... next time it hails i will take a few samples and if i get around to it i might photograph them and post it. ___Sweet! While driving in Kansas once a hailstorm hit with stones just slightly smaller than a baseball. I managed to pull off under an awning before it really let loose & it still ranks as one of the most awsome weather events I ever witnessed. It lasted about 3 to 5 minutes & made a sound like none I've ever heard. After it stopped, everyone's first interest went to rushing out to pick up the hailstones. Never mind the dents in the hood or broken windshields. :hihi: I broke one open & counted about 15 layers of ice. :cup: Quote Link to comment Share on other sites More sharing options...
CraigD Posted November 5, 2005 Report Share Posted November 5, 2005 … Given that a dimpled sphere (golf ball or otherwise) travels farther than a smooth sphere given the same applied force, may we assume these hailstones travel farther in the updraft & so stay longer & so grow thicker layers? …I don’t know if golf-ball like dimpling of hailstones has a significant effect on them, but if it does… The reason dimpled golf-balls fly further is that the dimples set up a boundary layer of air around the ball that reduces its effective aerodynamic drag. A hailstone with less drag would fall faster in an updraft, reaching the ground sooner (and having accumulated less ice) than a less aerodynamic one of the same mass. So, if you want really super hailstones, give them little, high drag parachutes, wings, or something, allowing them to stay aloft and gather ice longer. Its hard to imagine a way this could happen naturally, though, so I expect that the size of hailstones is determined more by the strength of the updraft, the amount of water available, and the coolness of the air layer that cools them enough to make them accrete ice. Quote Link to comment Share on other sites More sharing options...
Turtle Posted November 5, 2005 Report Share Posted November 5, 2005 I don’t know if golf-ball like dimpling of hailstones has a significant effect on them, but if it does… The reason dimpled golf-balls fly further is that the dimples set up a boundary layer of air around the ball that reduces its effective aerodynamic drag. A hailstone with less drag would fall faster in an updraft, reaching the ground sooner (and having accumulated less ice) than a less aerodynamic one of the same mass. So, if you want really super hailstones, give them little, high drag parachutes, wings, or something, allowing them to stay aloft and gather ice longer. Its hard to imagine a way this could happen naturally, though, so I expect that the size of hailstones is determined more by the strength of the updraft, the amount of water available, and the coolness of the air layer that cools them enough to make them accrete ice. ___On the bolded :cup: :cup: Because the air IS what applies the force right?___Now Jayq actually said 'slightly bumpy' then followed with 'like a golf ball'. A golf ball is 'bumpy' because of 'dimples'; what if the hailstone is 'bumpy' with protruberences? :cup: :hihi: Quote Link to comment Share on other sites More sharing options...
Jay-qu Posted November 5, 2005 Report Share Posted November 5, 2005 yeah it wasnt really the best example but the have a what seems to be a bit of both... slight dents and raised parts... Quote Link to comment Share on other sites More sharing options...
Turtle Posted November 5, 2005 Report Share Posted November 5, 2005 yeah it wasnt really the best example but the have a what seems to be a bit of both... slight dents and raised parts...___On further reflection I have to chuckle :cup: When does the bumpyness stop being dimply & start being protuberenty? :hihi: :cup: I mean every dimple has protuberent sides & every protuberence has dimply sides. :cup: :cup: Quote Link to comment Share on other sites More sharing options...
cwes99_03 Posted November 5, 2005 Report Share Posted November 5, 2005 when was the last time you examined a hailstone? Quote Link to comment Share on other sites More sharing options...
Jay-qu Posted November 5, 2005 Report Share Posted November 5, 2005 ___On further reflection I have to chuckle :cup: When does the bumpyness stop being dimply & start being protuberenty? :hihi: :cup: I mean every dimple has protuberent sides & every protuberence has dimply sides. :cup: :cup: well if you think of a virtual sphere and when a 'bump' goes inside the sphere it is a dimple, and when it raises above the sphere it is a protuberence Quote Link to comment Share on other sites More sharing options...
Turtle Posted November 5, 2005 Report Share Posted November 5, 2005 well if you think of a virtual sphere and when a 'bump' goes inside the sphere it is a dimple, and when it raises above the sphere it is a protuberenceYes..and...? Take your virtual sphere & populate its surface with protuberences. In so doing, you have inadvertantly populated it with dimples, which lie between & under the protuberences. Now do the opposite; start with the virtual smooth sphere & populate it with dimples. Voila, automatic protuberences. :hihi: Quote Link to comment Share on other sites More sharing options...
Boerseun Posted November 5, 2005 Report Share Posted November 5, 2005 well if you think of a virtual sphere and when a 'bump' goes inside the sphere it is a dimple, and when it raises above the sphere it is a protuberenceIs a zebra white with black stripes, or black with white stripes?:hihi: Quote Link to comment Share on other sites More sharing options...
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