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Information about this web site => Question related to Physics or physics related simulation => Topic started by: pradeep123 on December 16, 2008, 12:16:04 pm



Title: cork ball in water
Post by: pradeep123 on December 16, 2008, 12:16:04 pm
a cylindrical cup is filed with water. at the bottom (off center )a string is attached and the other end of the string is attached to a cork ball there by preventing it from floating. now the cup is rotated around its axis. what happens to the cork attached to string?

I am told that the string is slanted towards the axis . i thought it s slanting away from axis thereby providing the centripetal force, is it that the water is providing the centripetal force and the string is balancing it by slanting towards axis?


Title: Re: cork ball in water
Post by: lookang on December 16, 2008, 01:45:08 pm
My google search result:
http://physicslearning.colorado.edu/PIRA/PiraSubTOC.asp?STopic=1D52

Rotating corks in water    Corks tied to the bottom of two jars full of water are first translated on a cart and then put on a pivot and rotated about the center.   M-16c.1

strangely i search on http://physicslearning.colorado.edu:9999/vestris/PIRASearchBy.asp
but no hits:(
video not available ?

My request to you pradeep123
anyway please conduct the experiment and post the video here!




My reasoning:

The reason is the same for cork or sand.

The setup
1. string is to distract you into thinking about flotation law,
2. the rotation circular motion is to distract you into thinking of circular motion association with other circular motion effects, thus thinking of sitting on the vertical sides of the pail?


 read this from http://www.physicsforums.com/archive/index.php/t-124896.html
The effect is due to the speed of the water. Faster water will carry more and larger sedimentary particles than slower water. As the particles are tossed about in the water, they will remain suspended until they encounter a volume of slower water, where they will settle. Fast movement, and they will become suspended again.

So,

The slower water in the centre of the glass (or in the deep parts of a river) creates an area where the particles will have a chance to settle.


BTW, without this phenomenon, panning for gold would be fruitless. The gold is carried down fast-moving rivers and is deposited where the rivers slow briefly and can no longer suspend the heavier gold grains. This is a natural filtering-by-weight effect.


Stokes Law: Wiki (http://en.wikipedia.org/wiki/Sediment#Sediment_transport): "If a fluid, such as water, is flowing, it can carry suspended particles. The settling velocity is the minimum velocity a flow must have in order to transport, rather than deposit, sediments..."



My Question:
Can you make sense of it now? Discuss