Whirl pool action 2
First read the previous "Whirl pool action".
I put a six inch ball and the same six inch 2x4 into the pool and made a counter clockwise whirl pool.
The ball rotated about 10 times per revolution, and the 2*4 rotated about three time per revolution around the pool, both counter clockwise.
If this was a solar system, we could say the ball had 10 days per year, and the 2*4 had 3 days per year.
Both objects were placed at edge of the pool at the same place, about the same time. The ball made it to the center in about 5 years, the 2*4 made it to the center in about 15 years.
Both objects were about the same weight, why does the ball get the the center first.
I put a six inch ball and the same six inch 2x4 into the pool and made a counter clockwise whirl pool.
The ball rotated about 10 times per revolution, and the 2*4 rotated about three time per revolution around the pool, both counter clockwise.
If this was a solar system, we could say the ball had 10 days per year, and the 2*4 had 3 days per year.
Both objects were placed at edge of the pool at the same place, about the same time. The ball made it to the center in about 5 years, the 2*4 made it to the center in about 15 years.
Both objects were about the same weight, why does the ball get the the center first.
posted by Ragknot at
4:58 PM
15 Comments:
42. Soz, couldn't resist.
u shuda used a chicken and egg
the ball reached the center first because it was circular, therfore moved easier in the water, but the board was flat, and therefore met more resistance that the ball did.
Jacob,
That might make sense if the objects were porpelling themseleves. But both were being pushed by the flow. Neither were moving as fast as the flow.
I agree, the board friction's was greater, and it should have neared the water speed more than the ball.
The ball did not roll any as it moved with the flow. If it had any friction is should rolled wouldn't it? Like rolling over the ground? Instead is spun in a counter clockwise direction, exactly like the block of wood, but much quicker.
This post has been removed by the author.
Whatever the object is, it is both being carried along by the water and it is also pushing its way through due to inertia (it wants to keep going in its current direction at its current speed). This problem also re-highlights how complex the system is. It seems that both low and high density objects migrate to the centre.
Stop saying "friction", say "viscosity" instead. The physics is very different.
I have begun to brush up/re-learn fluid (emphasis on liquid though) dynamics, as I'd like to know what's going on just for the heck of it or failing that, to know why I can't know the answer.
Ragknot, I don't think anyone is going to be able to answer these whirlpool questions. I think they are very difficult. Although I reserve the right to be wrong about that. I firmly believe that a real whirlpool is a complex (almost chaotic) system. Greetz.
I agree with Jacob. The ball is circular therefore it is more arrow dinamic (I'm not exactly sure what that means, but I think it makes since. I'm just trying to sound smart.)
Obviously it is mentioned that the ball is circular and the 2 by 4 is rectangle for a reason. So My answer is correct.
Yes, Chris you are wrong. You don't have the amazingness to figure out the problem
I agree with jacob.
the ball has a shape to have less resistance (look at a ball in a wind tunnel vs a 2x4) water just like wind is made of waves so they would bend easyer around a curves edge than a 2x4 witch has 90degree edges if the water bends over these edges it would make a slightly less dence area of water (like a really fast un-aerodynamic car makes a air pocet witch has less air) that would give it more of a slowing down effect than the ball has.
This is purely speculation though a good idea would be to test a filed down 2x4 (same mass) with circular edges compared to the 90deg edges. both wil still be slower than the ball but i believe the filed wood would have less resistance
Ragknot, a small correction to my last post. Replace the first sentence of my last paragraph with "I doubt that you will get an intelligent answer to your whirlpool questions."
Anonymous 11:28 pm. Not sure if you're the one who claimed that I claimed "I know everthing" but if you check my last post, you'll notice that I freely admitted that I can't answer the question. Is that your idea of arrogance? So what's your problem (with me) - really? Are you not used to someone who talks in an honest, direct and straightforward manner?
I was using the idea of friction to show why it is NOT the right idea.
Let's look at an anology. Suppose we place the ball and block on a straight conveyor belt. The block will quickly assume the same velocity as the belt, but the ball with less friction, slowly get up to speed because it begins rolling and moves slower than the belt at first. The friction of the block enables it to get to speed quickly. The inertia of the ball causes it to roll and delays getting to speed.
Now in the circular flow, the ball gets to speed first, and leaves the block behind, so I don't see that friction has anything to do with it.
Now in the flow, the block has straight sides and square corners, I would think that the flow would push the block quickier. The ball has a smooth curved surface. Probably 1/10 of the ball in below the surface, where the block has about 1/2 the block is below the surface. The water displacement is approximately the same.
Why would the ball move so quicker?
Ragknot. Sorry about that ("friction" thing), I didn't phrase it very well. I hadn't intended to sound so harsh.
Part of the compliction is that there is likely to be a considerable difference in the moments of inertia of the ball and the beam. The rate of change of rotational speed will be inversely proportional to the moment of inertia and roughly proportional to the surface area in contact wih the water. The second follows because the viscous coupling force is proportional to the area in contact with the water, unlike friction which is only proportional to the mass. The viscous force is also proportionl to the velocity gradient near the objects.
The geometry will have some effect due to the shape of the flow lines around the objects, but I imagine that that effect isn't very important.
I hope you can see the glaring errors in the arguments and hopeless lack of understanding of physics presented in the post by Anonymous 12:20 PM and the almost total lack of understanding of reality by Anonymous 11:28 PM whose primary reason for posting was to take a pathetic and mindless poke at me.
But, how to solve your problem is remains beyond my abilities. At least I'm aware of that, unlike some Anonymous's round here. I know that you realise that it's not a straightforward problem either, and that you are just as curious as I am about it.
This post has been removed by the author.
That was my last reference to trolls. I'm starting to feel embarassed that I let them get to me. Normally I would probably have ignored such posts, I only responded as I did because they were making direct personal attacks on me.
Chris?
Do you think I don't know the answer to this? I do know the answer!
As you recently said, It's 42
If is not 42, then I am totally dumbfounded.
I tried the same experiment today, the block of wood made the same progress, it made it to the center right on schedule, but the ball never made it. It seemed to want to stay on one side of the pool.
I think I have the answer to this one... the wind won, because 90% of the ball was above the water line.
LOL. Hi Ragknot, I had thought of the wind possibilty (for the main problem), but didn't want to make it more complicated.
I'll confess that I also posted the chicken and egg one. LOL. Soz, but I was in a playful mood and I had recently posted a comment referring to the "which came first..." for the "A Circle Mystery" blog.
Post a Comment
Links to this post:
Create a Link
<< Home