Richard
Final Approach
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Ack...city life
Can an object fall faster than terminal velocity?
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jesse
Touchdown! Greaser!
Why does a large rain drop fall faster than a small one? It surely isn't because it is heavier like that article suggests. Is it because the profile of the drop changes based on its weight (resulting in less drag)?
I would think that the potential for a drop to break-up in flight and temporarily fly at a speed differing from it's terminal velocity would have already been thought of? The key thing is it it would be temporary -- one thing that article really doesn't mention.
Of course if that larger drop broke up -- it would be smaller by itself and would then slow as well (assuming that article is true and small drops drop slower). I would think some of this would balance itself out. The net product would be pretty similar. A drop can't suddenly just separate from the other one, go faster forever, and have the parent drop not change it's speed.
What exactly do they propose to fix this? I really don't think you're going to accurately model the potential for rain-drops to break up in flight real near their instruments. If they broke up at altitude it wouldn't matter because it'd slow to terminal velocity. The situation is dynamic as hell -- sometimes all you can do is go with the static constant.
Just my two cents...not a rain drop expert.
To answer the thread title....No..an object does not fall faster than its terminal velocity. I can dive in an airplane at 400 knots and jump out of it. I'll be going 400 knots, temporarily. I'm not beating physics. Of course a lot of this is just academic as the situation is very dynamic with a lot of variables at play.
I would think that the potential for a drop to break-up in flight and temporarily fly at a speed differing from it's terminal velocity would have already been thought of? The key thing is it it would be temporary -- one thing that article really doesn't mention.
Of course if that larger drop broke up -- it would be smaller by itself and would then slow as well (assuming that article is true and small drops drop slower). I would think some of this would balance itself out. The net product would be pretty similar. A drop can't suddenly just separate from the other one, go faster forever, and have the parent drop not change it's speed.
What exactly do they propose to fix this? I really don't think you're going to accurately model the potential for rain-drops to break up in flight real near their instruments. If they broke up at altitude it wouldn't matter because it'd slow to terminal velocity. The situation is dynamic as hell -- sometimes all you can do is go with the static constant.
Just my two cents...not a rain drop expert.
To answer the thread title....No..an object does not fall faster than its terminal velocity. I can dive in an airplane at 400 knots and jump out of it. I'll be going 400 knots, temporarily. I'm not beating physics. Of course a lot of this is just academic as the situation is very dynamic with a lot of variables at play.
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Richard
Final Approach
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Ack...city life
This phenomena is quite complex. The link below is to a different paper produced by the authors. In the article I originally linked, it is mentioned how the coalescence of drops can influence drop and droplet formation and then formation of air eddys.
http://ams.allenpress.com/archive/1520-0477/86/2/pdf/i1520-0477-86-2-235.pdf
Here they're talking of the influence of eddys on velocity.
http://ams.allenpress.com/archive/1520-0477/86/2/pdf/i1520-0477-86-2-235.pdf
Graueradler
Pattern Altitude
Doesn't the volume ( weight) of a sphere grow faster than its cross sectional area? If so, larger drops woul dfall faster than smaller drops.
poadeleted20
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Graueradler's got it -- it's all about sectional density (mass divided by frontal area). As the size of a sphere increases, its weight goes up faster than its flat-plate area (weight being proportional to the cube of the linear dimension, while area is proportional only to the square of the linear dimension), thus increasing the velocity needed to create an amount of drag equal to the weight of the drop (drag being proportional to area times velocity-squared).
BTW, I suspect that the reason the group of smaller droplets can fall faster than a single droplet of the same size has to do with the same effects which allow "drafting" in racing -- that a pack of race cars can go faster than one car alone. It's all about changes in the airflow around the group compared to airflow around the single car, resulting in two cars running together having lower total drag than the sum of the drags of two individual cars.
BTW, I suspect that the reason the group of smaller droplets can fall faster than a single droplet of the same size has to do with the same effects which allow "drafting" in racing -- that a pack of race cars can go faster than one car alone. It's all about changes in the airflow around the group compared to airflow around the single car, resulting in two cars running together having lower total drag than the sum of the drags of two individual cars.
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twdeckard
Pre-takeoff checklist
A long time ago I participated in some experiments that demonstrated that fat uncoordinated assymetrical skydivers fall faster than skinny experienced ones. A lot of it was chalked up to m * v.
I will henceforce tell people that my sectional density is simply different. Much more flattering than Body Mass Index.
Todd
I will henceforce tell people that my sectional density is simply different. Much more flattering than Body Mass Index.
Todd
fgcason
En-Route
Stupid question however: Are they subtracting out airmass movement? As time progresses during a rainstorm, the airmass itself starts descending. The principle applies on a large scale as well as a small scale. IOW, vertical component terminal velocity would constant within the air mass however the fixed location instruments observing the water drop movement would see an increased downward velocity.
They're talking about clusters of raindrops so add in the drafting effect that Ron mentioned along with small sections of reduced air resistance and some drops will descend faster than others.
Just a random thought that they probably already eliminated.
They're talking about clusters of raindrops so add in the drafting effect that Ron mentioned along with small sections of reduced air resistance and some drops will descend faster than others.
Just a random thought that they probably already eliminated.